I have a 1990 300E, and I have noticed that when driving it long enough for it to get hot, it spits out quite a bit of coolant and if your not driving it on the road, the temp gauge will start to climb above running temp. What could this be? Any advice will be helpful, thanks.

 

Sounds like the beginnings of a leaking head gasket. I had my head gasket go on a 1993 300e not long ago. It started with just the temp rising and falling alot while sitting still and then once a week having to add water and coolant. A couple months later, it finally blew out the gasket at the number 6 cylinder. Keep a close eye on it.

 

Agree with Thauber, you probably have pressure (compression) of the engine leaking in the cooling system and this causes the temperature to rise rather fast. It will also raise the pressure inside your cooling system and cooling liquid will be pressed out of the system, usually via the normal overflow outlets.

If you have a leakage at a different place (radiator, hoses, gaskets) you will be able to see that quite quickly. If the engine is cold you will find traces of the cooling liquid.
As soon as the temperature rises also the pressure rises and then the cooling liquid will be pushed out. Simply check your engine for leakages and if you don't see any you know your head gasket is leaking.

Another way of identifying a gasket problem is to look for white smoke when the engine is running. At the moment you will not see a lot since the leakage is small. Rev up the engine to high rpm, let go of the accelerator, let it run idle for a few seconds and rev the engine up again. If you then see a small plume of white smoke you know you have a leakage. Reason is simple, by revving up the engine you increase the pressure drastically, releasing the accelerator will cause a pressure drop and cooling liquid will be sucked into the engine. The moment you rev up the engine again it will come out the exhaust pipe.
Same if you start the engine, you should see a small plume of white smoke.


If it is a leakage it will be quite small, but my advice would be to change the gasket ASAP, that will save you come cost later on.
If you wait until the whole seal blows you will be required to flatten the cylinder head before changing the gasket (remember to take a slightly oversized gasket after flattening). If you change the gasket now you may get away without flattening the cylinder head.
Also, if the gasket blows you will get cooling liquid in the cylinder and that is the last place you want to have it, it will cause more damage.

Finally, don't put normal water in the cooling system. Normal water will cause corrosion and the calcium in the water will clog up the hoses, ruin your water pump, close the cooling channels in your engine and block the radiator. So always use cooling liquid or.......if you really want to use water use distilled water.
________
The Sanctuary of Truth Pattaya

 

check to see that your fan clutch is working properly also...if your entire cooling system is relying on the elec fan it may be getting too hot

 

just replied to forum above. I had exact same problem on my 300e, 103 engine. Just finished the job last week.
1. Take a compression check, cylinder 5 and 6 were low on mine by about 20 lbs.
2. My cylinder head was not warped so did not resurface, did do valve guides while I was at it.
They had some wear and it's not hard to do.
3. Radiator was also plugged some. Replaced that also.
got all parts from internet, spent less than $500

 

I have been having similar issues but cannot figure out what is happening:

I changed the coolant reservoir to a new one, i did not bleed properly and the heat gauge started going up, as soon as it did that i stopped the car. I then had a shop bleed it for me, right after they bled it the coolant started dumping, they mentioned that it just may be too much coolant. the next day i started having the same problems with the gauge going up to 120c, i of course pulled over and turned the car off immediately, I was able to drive home later that day, the gauge did the exact same thing, but when i checked the temps with a temp tool the car was not that hot, so i was thinking i still had air pockets, the heat also stopped working.

I bought a new thermostat and installed it, bled it again and eventually the heat started working and the car was no longer overheating. Car has been running better than before i changed the reservoir tank ( also to mention I was not having any issues at all before changing the reservoir tank ) but the coolant is still spitting out, temps are totally fine, heater works totally fine, no loss of power at all and no smoke coming out of the exhaust.

Any ideas?