COOLANT CONSUMPTION: OH NO..

[Bmwtvboy]

MY 234K MILES M54 engine system is using coolant. Not sure how much, but I can't seem to see any leaks on the driveway. Overflow tank was very low. Checking daily now. No overheat issues with this motor ever! What should my next course of action be to figure out if its the head gasket? Or something else?
Thanks.

[Crowz]

Buy a pressure tester.

This serves two purposes. One you will know when you fix the leak that its fixed.

Two it allows you to apply pressure and have a cold motor. This makes finding the leak much easier and a bunch less painful.

Apply pressure and then start wiggling and testing hoses and other areas.

[andrewwynn]

You can borrow from a car parts store. (advance Auto for example). You buy it but return for full credit.

I developed a hairline crack in my client reservoir. Coolant is florescent, you can use a UV flashlight to help find leaks. I was about to get the pressure tester when I found the leak on the side of the reservoir.

The stiffening plate on the bottom can catch a month of drips before any will come out on the driveway so if the leak doesn't jump out at you, you may have to remove the plate to see. (just make sure to replace the four aft bolts since they also hold the sway bar before you drive.

Common source for a slow leak is either the reservoir or one of the o-ring seals going in or out of it.

[oldskewel]

Agreed on the use of a pressure tester. You might need a special adapter to fit the coolant expansion tank.

But there's also something like this that directly checks for combustion gases in the coolant:
https://www.amazon.com/Lisle-75500-C.../dp/B0007ZDRUI

It would be a more direct test to rule out/in any head gasket problems.

It applies a vacuum to the coolant tank, and if any combustion gases are present (as they would be if you've got a head gasket issue), the test fluid in that little tube will change color.

[AV8R4AA]

My bet is under manifold coolant transfer pipe.
If it’s poopy Brown, it’s beyond it’s usefull life.

[Bmwtvboy]

This is great information. Get this, a month ago I had to buy a new tank cap. OEM, filled tank with coolant and drove from ME-FL about 1700 miles. Five days ago I was checking fluids.
That's when I noticed it was very low and filled it until the float stick came to the highest point. I also mistakenly over filled my oil by a pint during a change. Since these two updates I have clocked 1000 miles . Easily driving in the 2700-3200 rpm final drive. I am getting great mpg. Acceleration is flawless. Idles perfectly.
I even had to use AC yesterday. And sure enough, both the coolant and oil fluids remain exactly the same as five days ago. This is weird. If I were burning coolant some would be gone. I don't see any leaks. But I know my water pipes to block are original. Oh, no mayo on the oil cap. So I am going to check the plugs and try and get a compression test. If its all good, rebuilding the intake manifold side. Thanks for getting me started.

[Bmwtvboy]

Just did the compression test. Is it absolutely imperative to test on a warm engine? My was cold from last night. 50's. It was a wet test and it was weird. 120, 90, 100, 100, 120, 70 and that is 1 -6. I am not buying excessive oil and my plugs were of the proper color and wear after 34K miles new. I put them in after the Dvanos seals rebuild at 200K. What did I mess up? BTW, it drives great. Puuurrfect idle, good mpg, smooth acceleration.

[bcredliner]

Since you topped off the coolant and haven't lost coolant over the last 1000 miles, I would just check it frequently and also take a flashlight. Now if you are going to be driving long distances you should keep looking. Suggest you check heater hose connections and the water pump. Those type of leaks can be very small in the early failure stages.

[e39_touring]

Also check for residue/crust around the cap on the expansion tank. That seal can go, and you can loose small amounts of coolant as steam without really seeing/smelling it.

[Bmwtvboy]

Yes, water pump, forgot that one. But I am also thinking maybe leaking at the water hoses into block under the manifold. I don't think it's in the cylinders though. My plugs were toasty brown and idle is puurrfect.