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so I finally thought I had fixed everything to do with the coolant /oil leak issue when I fixed the oil cooler gasket but I guess not. I can’t for the life of me find the leak. The random add coolant message comes on the cluster. The car has 170k miles. There is absolutely no noticeable puddles on the ground when parked..
Walk around the car with the hood open while the engine is running. Smell for coolant odors, and use a bright LED flashlight to look in every hidden crevice. The circulation pump on my W166 sweated coolant odors from new (3,000 miles). It doesn't drip or leak, but the obvious sign of crusted coolant residue is seen on the hose fittings. The smell is most obvious when the engine is hot/fully warm for example after a long several hours' drive.
Also check your engine oil for signs of coolant. Do you have rough idle, or coolant (sweet) smell from the exhaust?
Thank you for the quick response. The idle is smooth and the car just had the engine oil cooler gasket replaced by me where coolant goes through. That’s dry as a bone. I am try to get a cheap pressure kit to put on the coolant expansion tank and see if the leak. You have any suggestions for a cheap kit?
Konigstiger gave you worst case scenario. I would start with the coolant level sensor. Chassis had good advice that I would add to by introducing UV dye into the cooling system as an additional inspection tool.
Internal leak such as mentioned in Konig's document, along with 170k mi, for me anyway, would translate to an engine swap. Easier just to throw a new motor in it. Are you M272 or M278?
so I finally thought I had fixed everything to do with the coolant /oil leak issue when I fixed the oil cooler gasket but I guess not. I can’t for the life of me find the leak. The random add coolant message comes on the cluster. The car has 170k miles. There is absolutely no noticeable puddles on the ground when parked..
I had a faint periodic coolant smell for weeks and it turned out to be the heater control valve by the firewall. Crusty coolant was forming around the fittings. Try checking there.
Thanks for the many responses. I ended up buying a pressure test kit from Amazon for $46. I am going to try and perform the test tomorrow. The uv dye is a great idea as well. I did check that part by the firewall as I replaced it 10k miles ago and it looks fine. Do you think I could get uv dye from Amazon? I just dropped $2,700 to rebuild the transmission which is running great. I don’t really want put a engine in it at this point as the leaking isn’t major at this time.
Make sure you get WATER SOLUBLE dye. Some is for gas, oil, and hydraulic fluid. It’s not water soluble and will just make a real mess in your coolant reservoir that will never go away. Trust me on this.
I have an update that I am pretty excited to tell everyone. I took the advice on this thread and used dye to locate the coolant leak. I used a dye and uv flashlight. The coolant expansion tank is the source of the leak. The tank has a hairline crack. The lime green color you see in the picture is the coolant leaking. I went with an aftermarket coolant expansion tank. I can’t really complain too much as the car has 170k miles. These things are bound to happen.
I had to replace mine shortly before I got rid of the car. It had an intensely annoying habit of puking a cup or so of coolant while parked AFTER driving. It never lost a drop WHILE driving, just afterward when it was parked. The M-B part was only something like $70ish or so, as I recall. Fixed the problem right up. I think it took all of about half an hour to replace it.
10-03-2021, 08:10 PM
