Overheating, hose failure in 1990 300TE
 

I was driving today and noticed the fan was staying on, which is unusual, temperature was a little high, usually halfway between 40 and 80, now creeping up to 80. I pulled over popped the hood and saw that coolant was boiling in the reservoir, but barely, it stopped as I noticed. I checked oil which was fine. I started to drive home watching the temperature and it kept creeping up til close to 80 and the boom, the lower hose from the water pump blew off the pump. I pulled over and got a tow.

What do you experts think happened? The temp gauge never showed close to red line.

Thank you in advance!

If the lower hose deteriorates to the point that it's really soft, it will collapse under pump suction. Most noticeable at higher RPM's. Did this happen on a highway?

It started to act up with slow local driving and failed at about 45 mph, I thought I needed to speed up to get engine temp down.

But that is interesting, it did fail at higher revs, and it felt really soft when I looked at it after it failed.

Pull and test the thermostat.

You also need to do a cylinder leak down and check for bubbles in the cooling system. This can be accomplished by blocking the lower hose fitting at the water pump, filling the engine with water through the now empty thermostat housing.

A leak down test is the only reliable way to test for a combustion chamber to coolant leak.

Are you reading the temp gauge correctly? Normal is about 85*C. Something’s not right if it reads 80*C and the coolant is boiling in the reservoir. Test the reservoir pressure cap.

Sixto
98 E320 wagon
02 C320 wagon

Lower hose should have had a spring in it to keep from collapsing under negative pressure. Did it have a spring in the hose? Also, I agree with Sixto, I think your thermostat should be rated for 87C, so it doesn't seem alarming at all that your temp is at 80C, which is well below MB standard operating temps of 87C - 105C.

Thanks for your responses, No spring in hose.

I did the bubble check, no bubbles, took out the thermostat and let it idle for 30 mins, temp stayed at it's normal level, about 50, I don't know if that means it is fixed...

What is this 50?

50% gauge sweep or 50C?

Pay heed to what Sixto had to say. 80/85 is not at all unusual. If its boiling while you see either of those values on the temp gauge, your gauge way be out of wack or the temp sensor on the cyl. head is faulty, causing an incorrect gauge reading. I would also consider what 97 SL320 had to say in post #4. This overheating may have blown your head gasket.

There is a disc on the end of the thermostat that is vital in blocking the bypass port, don't dive the car with thermostat removed. Testing the thermostat involves placing it in water then raising the temp until it opens. Stat opening temp is stamped on the stat.

Did you do a leak down test? What sort of bubble test did you do?

The 50 is 50C, which is where it has been since I got the car, 5 years ago. I drove it about 10 total miles without the thermostat to get a new one, which I installed when things had cooled down. Disregard the bubble test, I didn't do it right.

It drives fine and sounds good, I drove about 30 miles with the new thermostat.

Now I am thinking I should check out temperature sensors for the engine.

I replaced the 1 pin and 2 pin sensors in the top of the engine block, and now the temp reads about 87, warm start is much improved and rough idle when hot is eliminated. Thank you all for your help. It's a tough car!