'91 190E 2.6 -- coolant loss riddle
 

Oil -- normal usage. It has used about 1 qt per 800-1,000 miles since I've had it the last 3 1/2 years. This has not increased.

Coolant -- in the last few months, I have to fill the reservoir tank every 3-4 weeks. If not, it will begin to run hotter because, well, it is low on coolant.

Now, three things to keep in mind:
1 -- I've suspected that my aux. water pump was less than full strength but I've never had any leaks or other problems.
2 -- There is NO oil in the water, nor water in the oil. Both are clear and clean.
3 -- There are NO leaks under the car. Not oil, not coolant, not anything.

Where is the coolant going? The only thing I can suspect is that somehow the water pump loses coolant when running and since I don't let is sit still in the driveway and run all day, I don't notice the leak.

All fans work just fine. Otherwise, the car runs like a dream -- even at 191k miles.

Anyone?

There is a (block test) that checks for combustion gasses in the coolant system. You should for starters pull all the spark plugs and look for one or two that are differnt looking than the rest. This could indacate coolant in the cylinder.

Also sometimes when coolant is leaking from the heater core or wiper motor area it is missed because it travels down a drain onto the top of the trans and is spread about so much it doesnt drip much and then the exhaust cooks some off too.

Hope you find it.

Make sure the system is air-tight. Inspect the radiator cap and the coolant tank. After driving the car and getting it up to temperature shut it off and let it sit. After 10 minutes the hoses should still have pressure in them.

I agree with R P Ryan,

My 190E 2.6 was doing the same thing. I went crazy looking for the problem. One day while looking, my non mechanical son says, "do you think it's the radiator cap?" , I thought no, but changed it anyway....fixed!

I went thru this once with the same motor and finally solved the problem by performing a cooling system pressure test.

You can rent such a gadget at Auto Zone or perhaps another parts store in your area.

It won't do you any good to ponder where the leak is until you can pressurize the system. If this doesn't expose the problem, then consider a previous post above that suggests an internal vs. external leak.

Thanks. And...what will this test tell me? Does it pressurize to make the leak evident, like putting a bicycle tire tube in a tub of water so you'll see where the leak is? This is kind of sounding like a slowly failing water pump, I think.

My auto parts store let me borrow a pressure tester for free, fill the reservoir with water and hook the tester, pump it up to the psi shown on the rad cap and you will see the leak if the presseure is dropping.

Dan

I agree with Ryan to start by testing or replacing the pressure cap. Be sure it is the proper cap. I believe that car calls for 140 kilopascals. After that a pressure check is in order. There are two important points to remember when doing a pressure test. Don't go over the rating of the cap or you run the risk of rupturing the heater core. Secondly you can only do pressure check on a cold engine. If you do the test on a hot engine you will get mixed results.

Good luck,
Peter

In my 190e, it was the heater control valve that was leaking. This is the valve that regulates the flow of hot coolant to the heater core, and is situated near the wiper base area. When it leaks, it leaks into the transmission tunnel area.

If this is the cause of the leak, this is a DIY repair.

UPDATE:

Well, I didn't think it was serious. Turns out -- after a 1 hour pressure test -- that there was a pinhole prick in the upper hose. That's all.

Evidently, it was a very small hole and a fine mist, at hot temp it just vaporized. Therefore, no leakage. That hose was never even wet.

I think this thing may just run forever.

Congrats and see post #8. YOU CANNOT PRESSURE CHECK A HOT ENGINE.

Peter