Recently did some major work to my 95's E300Ds cooling system. Changed the Water-Pump, Thermostat, Water-Pump Housing, etc..) I consequently drained and refilled the system. Coolant temperature is fine, heats up quickly and maintains a steady 85C. Coolant level is also fine. The work was done about two weeks ago, and have driven about 500 Miles since. My question relates to trapped air in the cooling system

In the morning, when the engine is cold, and I squeeze the top radiator hose, I can feel, and hear that it is full of air bubbles. Is this normal? Do I need to bleed the system, or will this entrapped air eventually escape?

Thanks,

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

Have you started up the car from cold with the coolant pressure cap off and let the system run for about 10 minutes?

No, but what I have done so far is several times already, I removed the cap, (carefully) while the engine was HOT, to release pressure and hopefully let some of the air escape. So far, no change.

I'll try your suggestion next. But from what I desribed does that mean that I do have entrapped air?

Thanks,

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

When you replaced your thermostat did it have a little hole with a bearing in it? that is the bleeder ball valve that MB started putting in the thermos because air would get caught up next to the thermo and not allow it to open and overheat the system, you had to pull the radiator hose off and use a plastic wedge to open the thermo and allow the air to escape. Since MB started using this ball valve in the thermo I have not seen an issue with air causing the system to overheat. When you squeeze the top hose you will hear gurgling and air. But like beforementioned you should start when cold and run for about 10 with the cap off the resevoir to ensure all air is out. While it is running squeeze the top radiator hose a few to make sure all the air is out. Good Luck!

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Brian W. Heitman

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I have the same question, except my car is a 91 560SEL that I recently purchased. I have noticed the same sypmtoms with my car with the exception of it is now starting to excede the 100degree mark when driven more than 20miles. I will try the cap-off solution and get back with y'all. (engine will have to cool down first, I just drove in to work.)

Every time I do something with the coolant I have to "burp" the cooling system. You'll find this information several places if you do a search.

Take the cap off and elevate the car so that the overflow tank or wherever you fill, is the highest spot in the system. Mine's on the right side, so I pull the front right wheel onto the curb.

Let the car warm up to where the thermostat opens. Mine is about 80 C.

When it is warm, I rev it to about 2500 for a few minutes. That lets the water pump spin pretty good and the air will want to leave the system at the highest spot.

This works for me. What I usually see when there is a bubble is a big fluctuation at the temp gauge that has little relation to driving conditions, that is, slow driving can show high or low temps and the gauge swings much quicker than when there are no hot spots.

YMMV

I have the same model and year. I also recently did some cooling system work ( actually duo valve replacement) . I was told it would self bleed so i made no attempt to get rid of air.

After one trip the coolant reservoir had dropped a couple of inches but still above the warning sensor. I then just topped it up and have had no issues since. Hope this helps.

Keith

Thanks All,

Listened to your suggestions. From a cold start, left the cap off for 15 minutes while the engine was running. This morning all was OK

Thanks

Phil

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'95 E300 Diesel, 264,000 Miles. [Sold it]

I have a 380SE, 1985, and the same set-up was in my old '75 450se. If you notice, the resevoir is designed to fill the radiator from the bottom, to push the air to the top. The hose leading from the top radiator tank to the resevoir is designed to allow entrapped air to bleed to the top of the resevoir tank, out of the coolant as it circulates, but still within the sealed and pressurized circulation system.
The overflow tube from the cap is on the other side of the cap seal, and doesn't allow any loss of pressure (or air) until the cap spring is overcome. This design is quite different from most sealed systems, I think.
The highest point in the system is already inside the top part of the resevoir tank, where all the air entrapped in the coolant will eventually go. I see no need to manually elevate the car to 'burp' the air out.

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1986 560SL
2002 Toyota Camry
1993 Lexus