Cooling system leaking out of cap

[TBmas1]

Hey there everyone. I have a '99 540iT with 199k miles on it.

I've just gone through the majority of my cooling system- water pump, thermostat, valley pan, trans cooler regulator, most of the hoses. The radiator and expansion tank were swapped by the PO, but it is probably getting close to time for these as well.

Now that I'm complete with all of this, my radiator cap is leaking a slight amount of fluid each time the car is shut off. At first, I thought I may have overfilled, and that it is just burping out a little bit of additional fluid, but it is doing this every day. it isn't much fluid that I'm losing, maybe 2 or 3 oz each day, if that.

This all started when I blew the hose which ties into the front of the waterpump (the hose that ties into the Tee to the trans cooler regulator). The hose blew out as I was pulling into my driveway (lucky yes, I know). I immediately shut it off, and got the hoses on order. I broke the trans cooler trying to get everything back together, so it got swapped as well. Once I got everything back together, the water pump started leaking on day one, so it got swapped. The thermostat was changed out when I bought the car, about 6 months ago. Then, after the water pump, I started seeing the tell-tale drip at the bell housing, so the valley pan job got done. At that point, CVV was changed, as were vacuum lines, fuel injectors, and other miscellaneous parts.

And now, it is back together and I've started putting some miles on it. I noticed the radiator cap leak, so I went ahead and ordered a new one. This held back the drip for one day (maybe coincidence), but now it is dripping again. It isn't really enough to drop the coolant level, and I haven't yet needed to top up. This morning, I went ahead and rebled, thinking that pressure build-up from an air pocket could be causing this. However, the problem seems to be persisting.

When I checked temp with my scanner, it seems to hold at around 95 C, so that seems about right. The needle never drifts away from 12-o-clock, and it hasn't ever overheated (unless heat soak when that hose bursted). I'm at a loss. Most of the posts that I find point to a head gasket, but also are related to overheating problems which i don't seem to have. Could this just be more air? I plan to bleed later tonight when its cooled down further, and will bleed again in the morning, but this doesn't feel like the problem. Any advice is appreciated. I continue to drive it, but am concerned that I may be playing with fire, and the idea of a head gasket job doesn't sound like a ton of fun (plus my wife would be pretty pissed after the money I just spent on the last round of work).

Thoughts? Any advice is appreciated- the wealth of knowledge on here is astounding.

[R Shaffner]

I thought I had a leaking cap for a while too, with no overheating. I was about to order a new cap when I thought of the bleed hose and clamp that join the radiator near the cap (under the cover by the bleed screw). The hose and clamp were both were old and I had never messed with them. But the rubber had hardened enough so the hose had developed a slow leak at pressure. I tightened the clamp a turn or two and that solved the problem until I could get around to replacing the hose.

[TBmas1]

I thought I had a leaking cap for a while too, with no overheating. I was about to order a new cap when I thought of the bleed hose and clamp that join the radiator near the cap (under the cover by the bleed screw). The hose and clamp were both were old and I had never messed with them. But the rubber had hardened enough so the hose had developed a slow leak at pressure. I tightened the clamp a turn or two and that solved the problem until I could get around to replacing the hose.

Thanks!! I'll give that a try.
I must admit, I'm really wishing I had spent the money on some Evans waterless. I can't help but think that, now that the system is tight at the valley pan, it'll be searching out the path of least resistance and failing the last couple of parts that I didn't change (I should've listened to all of the advice on these forums to change EVERYTHING at the same time). How do I access the hose? Do I just need to pull the clip/cover at the shroud/bleed screw and reach in between from the passenger side?

It does seem like the cap though- when I thought it was failing, I took a look at the bottom of it, and it seemed like you could see the path where the coolant was escaping by a bit of discoloration. I'll try this anyhow and let you know how it goes.

- - - Updated - - -

And now, 30-40 minutes after getting home, it is making me out to be a liar- not a drop. not even a little. Maybe this morning's bleed took care of it, but I really doubt it. I'll check that hose.
If anyone else has some insight, lay it on me!

[edjack]

Is the rad cap from ebay?

[TBmas1]

Is the rad cap from ebay?

Nope- not an Ebay cap. It's a URO.
About 2 drips this evening- pretty par for the course.

[MotorMouth93]

Evans waterless coolant is crap I did a lot of research on it a while back, you did good avoiding it. There’s a reason no car uses it from the factory, if it was actually better you’d see it in high end supercars. The jist of it is that cars regulate engine temperature based on the temperature of the coolant because the relationship between the two is known. If you change the thermal properties of the coolant then that relationship changes, and in the case of Evans coolant it results in higher engine temperatures for a given coolant temperature since it doesn’t transfer heat as well.

What does the cap say on the top? It should say 200 for 2 BAR. Also URO isn’t very good quality.

If you want to reduce cooling system pressure just get a lower temp thermostat.

[Santaclaus4]

Evans waterless coolant is crap I did a lot of research on it a while back, you did good avoiding it. There’s a reason no car uses it from the factory, if it was actually better you’d see it in high end supercars. The jist of it is that cars regulate engine temperature based on the temperature of the coolant because the relationship between the two is known. If you change the thermal properties of the coolant then that relationship changes, and in the case of Evans coolant it results in higher engine temperatures for a given coolant temperature since it doesn’t transfer heat as well.

What does the cap say on the top? It should say 200 for 2 BAR. Also URO isn’t very good quality.

If you want to reduce cooling system pressure just get a lower temp thermostat.

Although some people on this forum have had good results with waterless coolant, I completely agree with the above statement. I too have done some research... well, googled it and came to the same conclusion.
Another two cents worth of opinion...The youngest of these cars is 15 years old. They have been operating at 108°C since some of the guys on this forum were in diapers. Changing the thermostat to 88°C now isn't gonna make much difference in the remaining life of the plastics.
Think of it this way. Eating right from when you were young is much more beneficial then starting better eating habits when you are 70.

[BimmrMeUpSnotty]

Nope- not an Ebay cap. It's a URO.
About 2 drips this evening- pretty par for the course.

URO! Well shoot! There’s the problem!

[geargrinder]

1. 100% corroborate Shaffnaff's tip on the top wiggly snake hose. Absolutely. That thing starts to go with time - or at least the end connections do - and is a sneaky beyotch leak because it leaks either down at the exp tank so you can't tell if its bleed screw or cap or what, or, drips ontop of the rad or down the other side making it look like a radiator or worse, mystery leak. The factory hose costs bux BTW. WTF BMW. In a jam or for a temp fix you might be able to nip 1/2" off the leaky end and stretch the accordion out to refit it and make a seal again. While I'm at it that thing re: how the whole exp tank and shroud and everything go on the car just suck a dead goat scrote. Esp when its fitted with Oetiker clamps so its hard as hell to disconnect when you want to pop the shroud/remove the exptank real quick. WTF again BMW, why didn't you make that tank easier to take the F out. One should be able to take the Exp tank off, then peacefully and easily remove the shroud, not have to do some kind of half-half mess while you fiddle with the stupid hose clamp. /rant

2. IME these motors (likely especially w the factory op-temps aka not the 88C t-stat) DO do a post-shutdown heatsoak thing. I am certain there's a little temp peak after you shutdown. I've had leaks a number of times (derrrr of course, its an M62TU... if it ain't leakin its probably empty...) and on the tiny minor ones, they'd always show up first in that "leaked mystery drops after parking but never spotted when running or immediately after shutdown!" symptoms...

3. Are you filling to the right level? Red peener only just up to the rim? Or maybe even a little underfilled from that? More air in that expansion tank, as long as the low-coolant light isn't flickering, is always better on these mutherfraggers.

Respectfully disagree w/ my friend from the North Pole on couple things.

4. Philly loves Evans and his car is probably the most powerful M62TU I (or anyone) has ever heard of, so, and he truly dailies the damn thing, so... can't really say its a problem. OK SURE indeed I do agree - for a lot of people that approach is overkill and perhaps a bit too much hassle (i.e. refilling in East BumFoo after a leak... ) but I think as an approach it has some validity for those who want to use it for whatever reason.

5. Doing the 88C thermostat now still is a perfectly good idea. There's all that new plastic (rad, exp tank...) and seals (valley pan) that are starting another wear cycle and why not make them last twice as long this time. Plus, even for the other plastic that is sure already brittled, I believe indeed that you can make it worse. I know of one specific E39 that has such heat brittling that the plastic on the firewall all crumbles under your touch and entire areas have crumbled away. My car has nothing like that. I'd like to ensure it never gets there. Very definitely not all cars are already max-brittled yet.

- - - Updated - - -

1. 100% corroborate Shaffnaff's tip on the top wiggly snake hose. Absolutely. That thing starts to go with time - or at least the end connections do - and is a sneaky beyotch leak because it leaks either down at the exp tank so you can't tell if its bleed screw or cap or what, or, drips ontop of the rad or down the other side making it look like a radiator or worse, mystery leak. The factory hose costs bux BTW. WTF BMW. In a jam or for a temp fix you might be able to nip 1/2" off the leaky end and stretch the accordion out to refit it and make a seal again. While I'm at it that thing re: how the whole exp tank and shroud and everything go on the car just suck a dead goat scrote. Esp when its fitted with Oetiker clamps so its hard as hell to disconnect when you want to pop the shroud/remove the exptank real quick. WTF again BMW, why didn't you make that tank easier to take the F out. One should be able to take the Exp tank off, then peacefully and easily remove the shroud, not have to do some kind of half-half mess while you fiddle with the stupid hose clamp. /rant

2. IME these motors (likely especially w the factory op-temps aka not the 88C t-stat) DO do a post-shutdown heatsoak thing. I am certain there's a little temp peak after you shutdown. I've had leaks a number of times (derrrr of course, its an M62TU... if it ain't leakin its probably empty...) and on the tiny minor ones, they'd always show up first in that "leaked mystery drops after parking but never spotted when running or immediately after shutdown!" symptoms...

3. Are you filling to the right level? Red peener only just up to the rim? Or maybe even a little underfilled from that? More air in that expansion tank, as long as the low-coolant light isn't flickering, is always better on these mutherfraggers.

Respectfully disagree w/ my friend from the North Pole on couple things.

4. Philly loves Evans and his car is probably the most powerful M62TU I (or anyone) has ever heard of, so, and he truly dailies the damn thing, so... can't really say its a problem. OK SURE indeed I do agree - for a lot of people that approach is overkill and perhaps a bit too much hassle (i.e. refilling in East BumFoo after a leak... ) but I think as an approach it has some validity for those who want to use it for whatever reason.

5. Doing the 88C thermostat now still is a perfectly good idea. There's all that new plastic (rad, exp tank...) and seals (valley pan) that are starting another wear cycle and why not make them last twice as long this time. Plus, even for the other plastic that is sure already brittled, I believe indeed that you can make it worse. I know of one specific E39 that has such heat brittling that the plastic on the firewall all crumbles under your touch and entire areas have crumbled away. My car has nothing like that. I'd like to ensure it never gets there. Very definitely not all cars are already max-brittled yet.

- - - Updated - - -

(and also yeah URO sucks)

[TBmas1]

OK. Thanks everyone for the responses. Point taken on the URO parts- I'll get something better on order or swing by the dealer. Will also get that hose ordered and get the hose clamp tightened up, and will check back in over the weekend with a big thumbs up once its no longer dripping.

Regarding fill level- in general, yes- this has been correct. Typically, I correct the level at the next cool down after a bleed, by siphoning out the extra fluid if its overfilled.

Is there a different part number for the 88 C thermostat?

BTW- I have the same brittled plastic firewall issue at the back of the engine. I've been meaning to strip a good one off of a fresher donor, just haven't found one yet. Not opposed to replacing with new, just trying to pace myself. This car is great, but it is also great at zapping several hundred dollars out of my wallet at a time. So, there the list of refurbs needed that I try to whittle down, and then the break-downs that always trump those wish list items.

I had an older MB spontaneously combust on me days after I bought the 540 (I'm sure it was jealousy), so the firewall issue is pretty top-of-the-list for me. If the firewall had been absent on the Benz, I'd have been roasted.

[Santaclaus4]

Respectfully disagree w/ my friend from the North Pole on couple things.
Very definitely not all cars are already max-brittled yet.

Good points. I hadn't thought about the "new" plastic parts. I was mostly picturing the hard and brittle wiring looms and hoses in the engine compartment.

[R Shaffner]

re: how the whole exp tank and shroud and everything go on the car just suck a dead goat scrote.

+1 on the rant. I might have more to add once I stop laughing...

[R Shaffner]

Is there a different part number for the 88 C thermostat?

BTW- I have the same brittled plastic firewall issue at the back of the engine. I've been meaning to strip a good one off of a fresher donor, just haven't found one yet. Not opposed to replacing with new, just trying to pace myself. This car is great, but it is also great at zapping several hundred dollars out of my wallet at a time. So, there the list of refurbs needed that I try to whittle down, and then the break-downs that always trump those wish list items.

I had an older MB spontaneously combust on me days after I bought the 540 (I'm sure it was jealousy), so the firewall issue is pretty top-of-the-list for me. If the firewall had been absent on the Benz, I'd have been roasted.

I think I got my 88C thermostat from ECS Tuning. Love it. About the firewall issue, I'm lost. Don't know what you mean.

[geargrinder]

Yeah the plastic part at the firewall ain't wallin' off any fire, that's for sure.

[TBmas1]

Yea- I took a second to actually think right after posting that- agreed- clearly that brittle plastic crap in front of the firewall was never intended as fire protection. Strike that previous comment. Thanks again for all the support and feedback.

I have a couple of other minor issues that I may be posting in the coming days if I can't sort through them on my own.