540i Radiator Replacement

[SW530]

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.

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You understand this only happens when the thermostat isn't yet fully opened and it's a temporary condition that maybe lasts just a few minutes?

[kallekula]

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.

Thanks for the answer!

[R Shaffner]

You understand this only happens when the thermostat isn't yet fully opened and it's a temporary condition that maybe lasts just a few minutes?

(I like nearly all your posts and don't want to argue. I'd rather talk about how nice your car looks in the pics, which is real nice, but...)

You lost me with that comment. With the 88C thermostat, my car warms up just like yours, but the thermostat opens before the MAP one does, so it lets my cooling system keep the operating temp around 93C. That's all the time. On the throttle or not.

With the 105C MAP thermostat, the temperature often (usually) climbs up to 105C or more, and it stays there until the engine is under sustained load. (Unfortunately, I don't get to drive often that way much, with it at sustained load. Wish I could.)

And about radiators, my choice for an upgrade would be to get an M5 radiator. I understand it's a plug and play with more capacity.

[SW530]

(I like nearly all your posts and don't want to argue. I'd rather talk about how nice your car looks in the pics, which is real nice, but...)

You lost me with that comment. With the 88C thermostat, my car warms up just like yours, but the thermostat opens before the MAP one does, so it lets my cooling system keep the operating temp around 93C. That's all the time. On the throttle or not.

With the 105C MAP thermostat, the temperature often (usually) climbs up to 105C or more, and it stays there until the engine is under sustained load. (Unfortunately, I don't get to drive often that way much, with it at sustained load. Wish I could.)

And about radiators, my choice for an upgrade would be to get an M5 radiator. I understand it's a plug and play with more capacity.

I'm not trying to argue, I apologize if I gave that impression. What I'm trying to do is understand by asking questions and exchanging information so I can learn. To engage.

What are the average ambient temps where you drive and how do you drive? My local ambient temps can range from -30f to 105f. I drive my cars hard maybe 15-20% of the time.. I'd do it 100% but I'm long past presenting a risk to anyone including myself. You're only 17 once.. if you're lucky. I'm asking because I'm trying to understand if those of you with lower thermostats are actually running (once warmed up to an average temp throughout the range of ambient temps you operate the car under) in what temp ranges and how much load you're putting on the car. Its my experience that once a thermostat opens it rises to an average temp 5-10f above the thermostat rating. It can go higher if the cooling system is not properly maintained or just specc'd too small for the car as designed. If a car has a 90f and a 105f thermostat installed I'd expect them to run at pretty much the same temperature unless the ambient temps are fairly low and the car isn't put under load.

About the M5 radiator.. an ideal we all should have thought of. Thank you. Last year I ran my 2003 540i/6 ten very hot laps on a 90ish F day.. and my temps didn't change from if I was going 80mph on the highway. So my system is adequate, but if I was improving the performance.. which has crossed my mind.. do you know if in addition to the radiator any other cooling system components are different? Water pump, coolant pipes, fan blades, fan clutch, aux elec fan, shroud, hoses? Any of it? I learn so much in these forums.

My car sat in the Texas heat for years. The paint was dull, rough, glazed over, and half the car had severe water spotting from very hard water, sun baked on. Pretty sure sprinklers were routinely hitting it and then it just dried in the sun.. over and over again. When I bought it I figured I'd just get it wrapped and make it a daily. In the months following discovered there was a ton of maintenance done on the car that the previous owner had no clue about, including a full Super Sprint exhaust.. I still put $4000 or so into parts including new tires.. maybe $5000.. but the paint.. uggh.. Some might remember my struggles using different products to bring the paint back. I actually had to power sand from 1500g - 4000g using the magic 3m discs.. and lots of products to cut and buff from there. So thank you for saying it looks nice.. I put weeks and weeks into that car just on the paint. I still need to repair the rear bumper (3 2-3" cracks) and the hood has a bunch of road chips I need to fill and then respray the hood.. wish me luck.. learning as I go.

[R Shaffner]

...I'm trying to understand if those of you with lower thermostats are actually running (once warmed up to an average temp throughout the range of ambient temps you operate the car under) in what temp ranges and how much load you're putting on the car. Its my experience that once a thermostat opens it rises to an average temp 5-10f above the thermostat rating. It can go higher if the cooling system is not properly maintained or just specc'd too small for the car as designed. If a car has a 90f and a 105f thermostat installed I'd expect them to run at pretty much the same temperature unless the ambient temps are fairly low and the car isn't put under load.

Agree that we're all just trying to share and learn. Thx.

The answer is "Yes, absolutely." The lower thermostat lets the engine run cooler. All of us with an 88C thermostat report average engine temps around 93C. When I still had the stock thermostat, I often saw the temp in the 107C-110C range. I never saw it below that after it got warmed up.

(Drivers of these cars with the MAP thermostat have reported it dropping below 100C on long mountain climbs. I've never seen that because I've never looked at it in that situation, or when I'm driving hard. Again, I bet it would drop while blasting down the autobahn, but I don't ever get to drive like that.)

I think some people are confused by the fact that the observed temp in these cars is always a little higher than the stat rating. (Like when I see 93C from my 88C stat.) I believe that's from how BMW has plumbed these thermostats, partly in the intake flow from the radiator. They're not just reading and adjusting the coolant temp on the way out of the head, like other systems do. In short, the stock system can easily cool the engine far below that, even when it's real hot outside. It's the thermostat that keeps the engine from getting cooler than the target level.

About the paint...wow. A lot of effort, but it sure looks good in the pics.

My current '02 is my second 540. Sort of a rescue. It needed a lot. It's running well now and I love how it drives. I need to tackle the cosmetics next.

[TiesTorN]

Its my experience that once a thermostat opens it rises to an average temp 5-10f above the thermostat rating.

that's because those rated values are the point where it starts to open, not fully open.

[R Shaffner]

that's because those rated values are the point where it starts to open, not fully open.

Good point.

Didn't you try a still cooler thermostat for a while -- something under 80C? What did you think, and what are you using now?

[TiesTorN]

Good point.

Didn't you try a still cooler thermostat for a while -- something under 80C? What did you think, and what are you using now?

yeah it was a heat modified 88c tstat. it was fine in summer, engine temps fluctuated between 70-95c depending on weather and load.

winter was a different story though when I noticed that it won't go higher than ~65c on cold days I thought it was time to get rid of it and buy a new one. using a regular 88c tstat now, unmodified.

[SW530]

Agree that we're all just trying to share and learn. Thx.

The answer is "Yes, absolutely." The lower thermostat lets the engine run cooler. All of us with an 88C thermostat report average engine temps around 93C. When I still had the stock thermostat, I often saw the temp in the 107C-110C range. I never saw it below that after it got warmed up.

(Drivers of these cars with the MAP thermostat have reported it dropping below 100C on long mountain climbs. I've never seen that because I've never looked at it in that situation, or when I'm driving hard. Again, I bet it would drop while blasting down the autobahn, but I don't ever get to drive like that.)

I think some people are confused by the fact that the observed temp in these cars is always a little higher than the stat rating. (Like when I see 93C from my 88C stat.) I believe that's from how BMW has plumbed these thermostats, partly in the intake flow from the radiator. They're not just reading and adjusting the coolant temp on the way out of the head, like other systems do. In short, the stock system can easily cool the engine far below that, even when it's real hot outside. It's the thermostat that keeps the engine from getting cooler than the target level.

About the paint...wow. A lot of effort, but it sure looks good in the pics.

My current '02 is my second 540. Sort of a rescue. It needed a lot. It's running well now and I love how it drives. I need to tackle the cosmetics next.

Thank you, great information. You're right, the actual running temp will always be just above the thermostat rating because it takes time for the thermostat to respond and thermostats don't always work exactly at their spec'd temp.. The goal after several minutes is a open thermostat so its out of the picture and to let the cooling system cool as well as its capacity allows under the ambient temps and load currently under.

I still don't see a reason I'd want to lower it.. never had any issue with bursting radiators or expansion tanks and I'm not convinced about the power issue, but I do have an outside vented CAI with a high flow K&N. Next time at the dyno I might measure what I have.. figure at the wheels it's about 240 or so.. you can usually subtract 20% from the BHP assuming you're making BHP in a 20yo car. I'll get that measurement and then the next time I go I'll swap in a lower rated thermostat and see what we get. You guys have at least convinced me to do that much.

Check out the Flex orbital buffers.. they'll keep you out of trouble as you work the paint. 3m makes great quality cutting and polishing compounds and if needed their magic discs which in effect "color sands" or flattens the paint, in my case they removed the waterspots from hell, and a flatter surface shines deeper and looks so much better. This is done to every high-end paint job and you can do it yourself if you're patient and use care. Good luck on it.

[seagreen323i]

Long mountain WOT pulls lower the coolant temp in my 540, usually when I'm really flogging the car ill see 95°C if it isn't hot outside.

Oil temp control is my main issue now and I'm not bending over and paying that price for a Gulf housing.

Sent from my SM-S901U using Tapatalk

[R Shaffner]

I still don't see a reason I'd want to lower it.. never had any issue with bursting radiators or expansion tanks and I'm not convinced about the power issue, but I do have an outside vented CAI with a high flow K&N. Next time at the dyno I might measure what I have.. figure at the wheels it's about 240 or so.. you can usually subtract 20% from the BHP assuming you're making BHP in a 20yo car. I'll get that measurement and then the next time I go I'll swap in a lower rated thermostat and see what we get. You guys have at least convinced me to do that much.

It's no secret that the plastic cooling system parts are common failure points for these engines. It's not just because of the plastic. Many of us think it's the higher-than-normal temperature and pressure that these parts are subjected to (along with old age, of course).

Back when I had everything stock, on my first 540i (a '97), the original stock expansion tank sprung a bad leak at 80,000 miles. And the stock radiator input nozzle (from the engine) suddenly broke off on a hot summer day (110,000 miles). So those are 2 times I was left stranded. The third was when my water pump seized at 75mph on the highway with no warning (no leaking or whine before it failed). So I got stranded in that car 3 times -- all from cooling system failures.

(There have been other leaks that didn't leave me stranded, like when the replacement BMW expansion tank cracked at the hose fitting by the bleed nipple. Or when the aux water pumps started leaking.)

When I got my current 540i (an '02), I replaced the water pump (of unknown history) when I fixed a some UTC leaks, and I replaced it again 50,000 miles later I replaced the chain guides. As for cooling, I switched to the 88C stat, put on the N62 fan and clutch, replaced all the hoses, and put on a 1.4 bar cap (still high in my opinion, but closer to normal pressure than the absurd stock 2 bar cap.)

Cooler engine. Less system pressure. More power on hot summer days. And no strandings over the past 70,000 miles.

[R Shaffner]

As for testing, just jump on the throttle sometime while your engine is warming up, and compare that to when the engine is good and hot, like after sustained idling or stop and go traffic. Big difference, especially when the DME dials back the power.

[TiesTorN]

As for testing, just jump on the throttle sometime while your engine is warming up, and compare that to when the engine is good and hot, like after sustained idling or stop and go traffic. Big difference, especially when the DME dials back the power.

↑ this. I was gonna write smth similar to this but I was too lazy to do it.

I used to notice this everytime I drive the car when using stock tstat (long time ago) and I was wondering why? some time later (and some research) I discovered that high engine temp was causing that effect, switched to 88c and been happy since. it's a day & night difference, you don't need dyno results for that.

[SW530]

It's no secret that the plastic cooling system parts are common failure points for these engines. It's not just because of the plastic. Many of us think it's the higher-than-normal temperature and pressure that these parts are subjected to (along with old age, of course).

Back when I had everything stock, on my first 540i (a '97), the original stock expansion tank sprung a bad leak at 80,000 miles. And the stock radiator input nozzle (from the engine) suddenly broke off on a hot summer day (110,000 miles). So those are 2 times I was left stranded. The third was when my water pump seized at 75mph on the highway with no warning (no leaking or whine before it failed). So I got stranded in that car 3 times -- all from cooling system failures.

(There have been other leaks that didn't leave me stranded, like when the replacement BMW expansion tank cracked at the hose fitting by the bleed nipple. Or when the aux water pumps started leaking.)

When I got my current 540i (an '02), I replaced the water pump (of unknown history) when I fixed a some UTC leaks, and I replaced it again 50,000 miles later I replaced the chain guides. As for cooling, I switched to the 88C stat, put on the N62 fan and clutch, replaced all the hoses, and put on a 1.4 bar cap (still high in my opinion, but closer to normal pressure than the absurd stock 2 bar cap.)

Cooler engine. Less system pressure. More power on hot summer days. And no strandings over the past 70,000 miles.

Some years ago while living in Bangkok I built a fast image processing machine that I left on 24/7. It had all the best water cooled equipment on it and worked great. Until it didn't. I had two 5 drive RAID5's that synced to each other so all my work (I spent 3 years traveling SEA making the best pictures possible that I planned to put into several coffee table books and to be used for art gallery presentation. This was a huge investment for me) on them. I was so confident in the machine I didn't do an off-site backup.. One day I come home after being on the road for a week and my machine is shut down and sitting in a puddle of red antifreeze. A $1.29 plastic connector broke, drenched the drives, lost everything. Was it heat cycling or just being hot 24/7? Or maybe it was a defective part. I don't know. But I became a big fan of air cooling with massive heatsyncs and large low RPM fans.

I've had two V8 BMW's and a 4banger BMW with plastic parts, one of the V8's I put 150k on after rebuilding the cooling system. About 40k was put on the 4banger E30 318is.. Not a single issue with the cooling systems at normal temps. They were just well maintained and the plastic bits being plastic bits were going to be changed every ten years.. both didn't last 10 years but that's when we'd decided to. Why? Because they were plastic and there was an industry wide problem with over 10yo plastic bits on most every brand.

I really don't notice a power difference when cold or hot.. but I have a CAI that draws air from outside the engine compartment.

[R Shaffner]

The stock intakes are cold air intakes. The stock airboxes might get hotter in the hot engine bay than CAI tubes like Dinan's.