540i Radiator Replacement

[QtheGenius]

I recently bought the VSL all aluminum radiator, as I would like to take it to a HPDE once or twice for the fun of it. Since I'm in there, what else should I do as part of maintenance in this area? I'm assuming new expansion tank and hoses at minimum. Water pump? Thermostat?

Note: this isn't prepping the car for the track work, just what else to consider/address when replacing the radiator.

'03 M62TU, 165k miles, 6MT, chain guides/V-pan VANOS replace around 135k. New alternator around 150k.

[Iamthebull]

It's a matter of how far you want to go, but motor mounts, fresh clutch fan, unless you want to do an electric fan conversion. Lower temp (88C) thermostat, hoses and expansion tank. If you really want to go extreme while you're in there, any of your pulleys, and check your power steering system for leaks.

[MotorMouth93]

FYI an 03 540 will likely need to have the ECU reflashed to avoid a P0128 CEL with a lower temp thermostat. DIYable but not trivial.

What to change depends on what you've already done in the past few years. If you don't know when the car had the cooling system overhauled then its probably time.

[SW530]

When I did mine.. I bought a new OEM radiator (Behr), water pump with metal impeller, new seals for the pipes that run under the manifold, valley pan gasket, all hoses, regular thermostat (I personally would not recommend a lower temp thermostat), new water pump pulley (they're plastic and you stand a good chance of breaking it during removal, serpenine belt, belt tensioners and pulleys, radiator rubber mounts (the old ones crack and don't flex as they should), clutch fan, fan blades, expansion tank, the fan shroud, and with everything off I inspected the power steering lines, motor mounts, and anything else that needed service. I also took the time to plug in my steamer and clean up the engine and engine bay. What's left I'm saving for this spring which is to replace the VANOS (scoping inside the timing chain cover shows new sprockets and chains and the guides seem fresh too) and I'll put the valve covers in the blast cabinet and strip them down before Cerakoting them the proper color. The series of Cerakote I'll be using is good to 4400f and is normally used to coat internal engine parts like pistons and rods so I'm sure the valve covers will hold up fine for just about forever. The previous owner painted them a wild blue color and that has to change..

So it's all a matter of what your car needs and how far you want to go. BMW parts have date codes on them so note those codes as you remove them and you might find they've already been replaced recently and there's no need to replace them.

I track cars as my main hobby and last spring I ran 10 very fast laps on a 95f day and had no issue with the stock cooling system. If the stock cooling system in operating optimally, and the engine is as well, you won't have an issues. If you added a forced air system, turbo or supercharger, and upped the power levels significantly then its worth upgrading the cooling system.

Also, I used BMW coolant as specified, and Purple Ice wetting agent. I also like the Redline wetting agent. A proper wetting agent will raise your boiloing point by 10-12 degrees and you'll probably get more benefit from that then an aftermarket radiator. And don't forget to steam clean your A/C condenser so you get max air flow. People tend to skip that and reduced air floor reduces how well the cooling system can cool and all the aftermarket parts you throw at it won't make up for that difference. So steam and clean the condenser or if it's really bad just replace it.

Good luck.

[QtheGenius]

SW530, great notes! I have a basic steamer and I'll break that out while I'm in there. Motor Mounts, fan clutch, and pulleys I'll add to the list, belts and tensioners were also replaced with the Chain Guide replacement. Fan shroud is good, I don't see myself replacing it unless it's broken. I have to look at the records if the water pump was replaced or not. I also replaced the PS pump, and I believe I did a fluid flush about ~15k miles ago.

I think i'll stay at the standard thermostat. I've seen both sides of the debate of running cooling is never a bad thing on these cars, but also that there was a reason it was designed to run at the OEM temp.

[kallekula]

How many people rebuild the thermostat system? Why didn’t BMW do it when they designed the engine? Engineer miss or experiment or why? Shouldn't there be a recall if its that bad? Must be a reason for the engine running at the temp that it does?

[SW530]

How many people rebuild the thermostat system? Why didn’t BMW do it when they designed the engine? Engineer miss or experiment or why? Shouldn't there be a recall if its that bad? Must be a reason for the engine running at the temp that it does?

Back before emissions and smog/air pumps most thermostats were 180. Even back then guys liked to lower them to 160. If you were tooling around town on a cold day and had a good cooling system the cars would run at 160.. until you started working them even a little. And then they'd rise to what the ambient temps and the cooling system capacity and design allowed, if running the car hard this was often above 200 no matter what thermostat you had installed. Running the car with no thermostat would allow it to run at cooler temps just like a 160 but often even lower.. until you started pushing the engine harder. A popular fix on early Mustangs was to either change out the radiator support for one from a big block car, or cut it out and drill holes to accept a big block radiator thereby adding capacity. Today multi-row aluminum radiators add capacity via the extra rows and subsequently adding depth to the radiator dimensions. Some would add water pumps with different impeller designs or today electric water pumps to pump water faster. the idea is to get it to to radiator and it's air flow sooner. But you can have the water flowing too fast which reduces the cooling capacity. Other tricks were to make sure the cooling system was in really good condition and then increase the radiator cap poundage. Every pound of pressure you added raised the boiling point just over two degrees. Too much pressure and you'd develop leaks. We'd also optimize air flow via different or electric fans and better designed shrouds. Timing of course can affect engine temp, too far advanced and the temps could get out of control, but increasing timing is something you do when tuning an engine for more power. Whatever you did for improvement could be overdone setting back cooling capability.

With modern cars emissions became a priority and you'd burn more hydrocarbons during engine operation the hotter the engine ran, to a point. 210-212f was ideal and your fuel delivery and timing would all be optimized too make less emissions once the engine reached its ideal design temp.. so getting cars up to their max designed temp faster helped reduce overall emissions. On a modern car, lets say you live in an area with colder ambient temps and don't push the engine too hard and you put in a cooler thermostat.. you don't reach the temp the engine is designed for.. and very few bother to tune their engines so less fuel and less advance timing is being ran to compensate for the lower temps.. so you produce more emissions and more carbon is being formed and left on top of the pistons, in the head ports, valves, etc.. But despite all this, no matter what you do with the thermostat the engine is going to find it's max temp because of a combination of engine tune, cooling capacity, ambient temps, and the load the engine is being subjected to. Maybe you won't warm up as fast if you're not stressing the engine, but that really isn't a good thing unless you've designed and tuned your engine for those temps.

There is a lot to know about this stuff and certain motor sports like drag racing and track use benefit from some changes.. but it should be approached with all factors being considered, just not the thermostat.

[SW530]

One more thing most don't think about when adding an aftermarket multi-row radiator. I've tested this using a E34 radiator fan I had extra and a single row OEM radiator that was about 18yo, a new of the same, and a three row aluminum (expensive) radiator and a Kestral wind meter.

Before working in my E39 cooling I wire tied the E34 fan on the front of my condenser blowing air towards the engine and with the engine off blew air through the condenser and old OEM radiator. Really, you could barely feel air coming through on the radiator side.

After steam cleaning the condenser the flow more than doubled.

Removing the 18yo radiator and putting the new OEM same manufacturer radiator in almost doubled it again.

Pulling out the OEM radiator and placing a brand new Fluidyne 3 row for another project.. flow was cut more than in half.

I'm curious how a new condenser flows compared to my old cleaned one.. but that's for another time.

The point of this is air flow is vital but so few actually clean their condensers which we all know are right in front of the radiator.. and that multi-row radiators reduce air flow significantly. So much so I personally won't use one unless I can also replace the fan/shroud system to make up for that loss of flow.

[TiesTorN]

Must be a reason for the engine running at the temp that it does?

only reason is the emissions. also maybe slightly better mpg... that's all. other than that there is absolutely no benefit. high temp has more cons than pros.

[QtheGenius]

One more thing most don't think about when adding an aftermarket multi-row radiator. I've tested this using a E34 radiator fan I had extra and a single row OEM radiator that was about 18yo, a new of the same, and a three row aluminum (expensive) radiator and a Kestral wind meter.

Before working in my E39 cooling I wire tied the E34 fan on the front of my condenser blowing air towards the engine and with the engine off blew air through the condenser and old OEM radiator. Really, you could barely feel air coming through on the radiator side.

After steam cleaning the condenser the flow more than doubled.

Removing the 18yo radiator and putting the new OEM same manufacturer radiator in almost doubled it again.

Pulling out the OEM radiator and placing a brand new Fluidyne 3 row for another project.. flow was cut more than in half.

I'm curious how a new condenser flows compared to my old cleaned one.. but that's for another time.

The point of this is air flow is vital but so few actually clean their condensers which we all know are right in front of the radiator.. and that multi-row radiators reduce air flow significantly. So much so I personally won't use one unless I can also replace the fan/shroud system to make up for that loss of flow.

Even more great info. I'll definitely clean the condenser while I'm in there. Does it matter if you use steam vs compressed air?

[SW530]

Even more great info. I'll definitely clean the condenser while I'm in there. Does it matter if you use steam vs compressed air?

Compressed air is a lot of pressure, if the radiator is out I suppose you could try it being aware the pressure might screw up old cooling fins on the condenser.. that's what my mine imagined and is why I reached for the steamer and not the air hose.. the steamer is a nice low pressure heat that just melts off the dirt and bugs.

[SW530]

only reason is the emissions. also maybe slightly better mpg... that's all. other than that there is absolutely no benefit. high temp has more cons than pros.

True, better emissions, more MPG, less carbon build up internally, and if using the stock tune more power. I consider all those benefits. Colder temps than the car is tuned for does the opposite. So I don't see where a colder thermostat offers any benefit to a stock tuned car over running the car at the temp it was designed for. Unless you're talking about higher temps than designed for, like if the cooling system is impaired because of poor maintenance. What most don't get is the thermostat is not the final arbiter of the temp an engine runs at when under even moderate load. It just takes longer to get to the temp where you get the better emissions, less carbon build up, more power, and better mileage.. and for the life of me I can't see why a person would want that?

[R Shaffner]

True, better emissions, more MPG, less carbon build up internally, and if using the stock tune more power. I consider all those benefits. Colder temps than the car is tuned for does the opposite. So I don't see where a colder thermostat offers any benefit to a stock tuned car over running the car at the temp it was designed for. Unless you're talking about higher temps than designed for, like if the cooling system is impaired because of poor maintenance. What most don't get is the thermostat is not the final arbiter of the temp an engine runs at when under even moderate load. It just takes longer to get to the temp where you get the better emissions, less carbon build up, more power, and better mileage.. and for the life of me I can't see why a person would want that?

Well, these engines were designed to run over a wide range. The MAP thermostat will always be open at 105C, and it will open earlier under load, all the way down to 85C. And the S62 has a 79C thermostat. So it doesn't seem that the folks at BMW think higher temps are better for more power with these engines.

I bet the MAP thermostat works great for German driving. Hotter for better efficiency, cooler when blasting down the Autobahn. And I bet it never gets that hot there.

In NC, where I live, these engines dial the power back a LOT when they're that hot and intake air is hot. I switched to the 88C stat and it gives me much more power from stop lights on hot summer days.

[analyte]

FYI an 03 540 will likely need to have the ECU reflashed to avoid a P0128 CEL with a lower temp thermostat. DIYable but not trivial.

What to change depends on what you've already done in the past few years. If you don't know when the car had the cooling system overhauled then its probably time.

Will you expand on this reflash? I have a 03 as well so I'm interested in what to flash to avoid the CEL for the lower temp. Thanks!

[SW530]

Well, these engines were designed to run over a wide range. The MAP thermostat will always be open at 105C, and it will open earlier under load, all the way down to 85C. And the S62 has a 79C thermostat. So it doesn't seem that the folks at BMW think higher temps are better for more power with these engines.

I bet the MAP thermostat works great for German driving. Hotter for better efficiency, cooler when blasting down the Autobahn. And I bet it never gets that hot there.

In NC, where I live, these engines dial the power back a LOT when they're that hot and intake air is hot. I switched to the 88C stat and it gives me much more power from stop lights on hot summer days.

All cars engines are designed to operate over a wide range, from the coldest the engine is rated for, to right over the thermostats max rating. MAP thermostats simply account for the load of an engine when the thermostat isn't yet fully open, allowing coolant to reach the radiator under heavy loads like going up a steep incline or heavy acceleration, any condition of load where higher temps might be realized very quickly before the normal mechanism of the thermostat opens. A good idea, but again it's mostly for emission/efficiency.

I wouldn't say because one model comes with a 79c and another an 85c and yet another a 105c, that this means BMW doesn't think higher temps make more power. An engine designed for a 79c will make more power at say 81c than 50c. And so on.. Each engines design, ECU programming, cars purpose, technology employed, emissions requirements, and more determine the engines ideal operating temperature. Comparing just the operating temperature among different models is leaving out a bunch of other data you should be considering.

The fact is, air charge temp affects density and a hotter charge air means less oxygen is being pumped into the cylinders which means less power output. Compress that air like you do with a power adder (turbo/Supercharger) and the effect is that much more noticeable and measurable. Anyone who races a vehicle with a power adder can tell you chapter and verse about effect and methods to overcome it from air intercoolers to water or glycol intercoolers to CAI systems. My supercharged Cobra Mustang has a custom CAI that places a high flow K&N filter in the high wheel well with ducting directed to that filter. Every bend in the pipe, every bit of pipe width, all contribute to more/less power. Instead of an intercooler, even the type where you can add ice, I instead went with a methanol injection using SNOW parts. I have pictures I can share of the install if you're interested that shows how I located a much bigger pump than usual closer to the reservoir and used larger than normal tubing for more volume, and easily adjustable computers so I can inject more/less depending on ambient temps and humidity. I've spent hours on the dyno at different times of the year making tunes I can change to that correspond to the meth flow.. someday I hope to have a meth computer that talks to the ECU and saves me all the work. So sure, charge air can affect apparent power, but think about how long that power will last from that stoplight and how many other variables its affecting on your engine. People often don't realize the small stuff like the oil you choose and the temps it best lubricates at and how cooler operating temps could very well result in more engine wear.

The bottom line is that BMW engineers who really know their stuff spend hundreds of millions of dollars and years of testing and research to provide an "overall" ideal operating temp range. If power or any other variable could be improved without paying a price elsewhere by changing a $80 thermostat don't you think they'd have thought of that? Racing/tuning a custom engine for a single purpose, say drag racing, power and the engine holding together long enough for an event or even a single run before tear down is one thing.. add efficiency for road racing and track cars because refueling costs time.. But a transportation car? I just don't see any benefit outweighing the other variables it affects. YMMV..

[R Shaffner]

If you come drive my car in traffic on a hot day, you might. And if you ever have a plastic cooling system part fail from higher temp and higher pressure, you might. I've driven 540s for 20+ years over 250,000 miles. Some with a MAP thermostat and some without. I have to say that I like the compromises without much better.

- - - Updated - - -

Will you expand on this reflash? I have a 03 as well so I'm interested in what to flash to avoid the CEL for the lower temp. Thanks!

On my '02, I can see the thermostat error with INPA, but there's no CEL. I don't know whether an '03 would be different.

[SW530]

If you come drive my car in traffic on a hot day, you might. And if you ever have a plastic cooling system part fail from higher temp and higher pressure, you might. I've driven 540s for 20+ years over 250,000 miles. Some with a MAP thermostat and some without. I have to say that I like the compromises without much better.

.

I don't doubt your car feels like it has more power on hot days. A cooler running engine means cooler air in the engine bay which becomes your charge air.. I just am not willing to pay the price for the other variables and really I'm not interested in driving a car where the load is such that the temps don't rise to their normal temps anyway. Do you really think that once a 82c fully opens and a 105c fully opens there's any difference at all to a engine being worked even fairly hard? When they're open its like they're not there, the thermostat doesn't matter.. only the condition of your cooling system and the load the car is under will determine the max temp.

Are your sure the radiators that blew on you did so because of the operating temp and not the age of the radiator or the manufacturers build quality? The only leaking or blown BMW radiators I've seen were inferior products whoever installed before I bought the car and corrected the problem for.. Sometimes there is just a defect but I've been lucky with the ones I use (Behr).

[TiesTorN]

True, better emissions, more MPG, less carbon build up internally, and if using the stock tune more power. I consider all those benefits. Colder temps than the car is tuned for does the opposite.

no... ~92c vs ~108c won't have a significant difference on carbon buildup. majority of the cars operate at around 90c anyway. according to this logic s62 should have serious carbon buildup issues at ~80c operating temp. is that the case tho? no.

what do you mean "by design"? these cars are not carburated cars, they have maps for every situation. if your engine runs at 90c, it will adjust accordingly.

105c tstat can never make more power, just forget about that. there is a reason why 105c tstat allows cooling all the way down to ~80s @ high loads. unfortunately it's not happening fast enough to make any difference.

there is a considerable difference in power between 105c and 88c, we all felt it. and protecting your plastic parts from excessive heat is another plus.

from what I've seen, emissions is the biggest reason for a hotter tstat, plain and simple. you can do whatever you like of course. to each his own...

[SW530]

no... ~92c vs ~108c won't have a significant difference on carbon buildup. majority of the cars operate at around 90c anyway. according to this logic s62 should have serious carbon buildup issues at ~80c operating temp. is that the case tho? no.

what do you mean "by design"? these cars are not carburated cars, they have maps for every situation. if your engine runs at 90c, it will adjust accordingly.

105c tstat can never make more power, just forget about that. there is a reason why 105c tstat allows cooling all the way down to ~80s @ high loads. unfortunately it's not happening fast enough to make any difference.

there is a considerable difference in power between 105c and 88c, we all felt it. and protecting your plastic parts from excessive heat is another plus.

from what I've seen, emissions is the biggest reason for a hotter tstat, plain and simple. you can do whatever you like of course. to each his own...

Have you felt it, or have you measured it?'

If the MAP's adjusted for any thermostat you installed you wouldn't be seeing errors. If the fuel mixture isn't adjusted and you're running cooler than designed you're getting more carbon build up. You're also polluting more. And cooler oil lubricates less resulting in more engine wear. If there were no costs then the people who designed them would spec the car with a cooler thermostat. Maybe you're right and the cars defy how everyone knows cars work.. but until it's measured and the other variables are verified not an issue.. no thanks. Instead I'll worry about keeping my cooling system well maintained and ensuring max airflow and continue to enjoy OEM rad's that don't blow up..

[QtheGenius]

SW, I'm in your boat. My brother put a low temp thermostat in his e38, and loves watching the temp on his dash when he opened up the "secret menus" and can view that. I didn't fully understand why he did it either because he isn't an aggressive driver, just puts on highway miles between cities on the East Coast. But he's convinced that lower is better. I guess when he fails the next emissions check, he'll have to go back to what was engineered.

[TiesTorN]

If the MAP's adjusted for any thermostat you installed you wouldn't be seeing errors. If the fuel mixture isn't adjusted and you're running cooler than designed you're getting more carbon build up.

I'm not seeing any errors. only 2002-2003 cars are having that error. it's just a simple software coding, nothing important.

who said the fuel mixture isn't adjusted? it's contantly being adjusted according to the readings from the sensors.

you have some valid points about using stock tstat but most of your claims about using a cooler tstat are plain wrong. you are not damaging anything by using a 88c tstat. if this discussion was about a cooler tstat, for example 70c, then you may have had a point.

btw; I passed TÜV smog tests several times with the 88c tstat. it's not affecting the emissions as much as you think.

[MtnGn]

I replaced my prevanos M62 OEM tstat with the 88c tstat a couple of years ago. No problems passing emissions. No other problems noticed.

The warmed car used to run with the thermometer indicator straight up at all times. Now, in cold weather on the highway, the indicator will sit slightly to the left of vertical (cooler). I haven't cracked the on board computer yet to see actual temps in real time.

[R Shaffner]

Do you really think that once a 82c fully opens and a 105c fully opens there's any difference at all to a engine being worked even fairly hard? When they're open its like they're not there, the thermostat doesn't matter.. only the condition of your cooling system and the load the car is under will determine the max temp.

We might have to agree to disagree, and I don't want to take over the thread. But let me respond to several points.

1) I'm not talking about putting the engine in a temperature range car it's not designed for. Clearly, since the MAP thermostat is designed to open up at 85C when under load, my 88C is within the range. (That gives it a normal operating temperature around 93C.)

2) My answer to your question above is "of course I think there's a difference." Again, BMW thinks there's a difference too. That's why the MAP thermostat is designed to open up at lower temps when the engine is under load.

3) Yes, I agree about the point that when a thermostat is open it's like it's not there. That's also NOT what we're talking about. We're talking about when an 88C thermostat is open and a 105C thermostat still is not.

Let me put it this way. I drive a manual because the car can't know what I'm about to do. It can't anticipate. It can only react. That's what the MAP thermostat does. It opens up at cooler temps only after the engine is under load. I don't like that. I like keeping the engine in a more normal range so it's ready with more power whenever I ask for it.

And finally, I think the main issue isn't theoretical about heat and combustion efficiency. It's about thinner hot air, and also about how the DME dials the power back when the engine and intake air are both hot (probably to prevent knocking). I've driven this car for 20+ years, and I hate how summer heat saps power from this engine. I can't control how hot the ambient air is, but I can control how hot the engine usually is.

[SW530]

I replaced my prevanos M62 OEM tstat with the 88c tstat a couple of years ago. No problems passing emissions. No other problems noticed.

The warmed car used to run with the thermometer indicator straight up at all times. Now, in cold weather on the highway, the indicator will sit slightly to the left of vertical (cooler). I haven't cracked the on board computer yet to see actual temps in real time.

I'm not sure if it's the bluebus allowing it.. in fact their website says it doesn't work.. but I can set the active temp to show up on my nav screen.

[TiesTorN]

Clearly, since the MAP thermostat is designed to open up at 85C when under load

it's actually 80, not 85

88 is well within the range.