Overheating '87 300D Turbo - PeachParts Mercedes-Benz Forum

arnoneh · #1 08-17-2007, 04:04 PM

Have not had a chance to troubleshoot this since it just happened and I had to get back to work, but my sedan just overheated and started dumping radiator fluid (about a quart or so?) out of the overflow hose. A quick check of the engine compartment didn't reveal any broken hostes that so my first thoughts were:
- the fluid was so low the engine overheated and it blew off this fluid as a result.
- the water pump stopped working causing the engine to overheat.

I've got to go troubleshoot this after work....Any other thoughts?

Thanks ahead of time for the help. -harv

Brian Carlton · #2 08-17-2007, 04:07 PM

What were the exact circumstances when the overheated engine was noticed?

Please provide all details as to vehicle speed, vehicle load, ambient temperature, grade, engine running time, etc.

Also, please provide a history of this engine. What were it's typical operating temperatures when it was running "properly".

Whether it overheated due to typical high engine load in high ambients or whether it overheated due to a specific failure needs to be determined.

arnoneh · #3 08-17-2007, 04:16 PM

Its an original engine from the '87 diesel with about 200K on it. Been running fine without anything but regular services for the last 2+ years. leaks a bit of oil as do most of these engines. We're due for a 60K service I think.

I drove about 10miles total (from work, to the emissions testing station and then to my wife's work) at which point I noticed the fluid coming from the escape port behind the R-front wheel. So normal in-city driving, not hot out, no special load.

In the course of these 10 miles I didn't notice the temp peg, so I'm hoping I didn't damage the engine....but then, I wasn't really driving too long.

Brian Carlton · #4 08-17-2007, 04:23 PM

Quote:

Originally Posted by arnoneh

In the course of these 10 miles I didn't notice the temp peg, so I'm hoping I didn't damage the engine....but then, I wasn't really driving too long.

What did the temperature gauge do during the 10 miles prior to the overheat?

If you didn't look at the gauge during these 10 miles, kindly be honest about that.

arnoneh · #5 08-17-2007, 05:41 PM

That's what I meant when I said I didn't notice the temp peg during the 10 mile drive....I didn't notice the gauge. Prior to today it has always run at normal temp, although I don't normally drive it since it is my wife's car. -harv

badgator · #6 08-17-2007, 05:43 PM

Original #14 head finally cracked?

arnoneh · #7 08-17-2007, 05:45 PM

Let's hope that's the worst case senario.

What about the water pump...how do I test that?

Brian Carlton · #8 08-17-2007, 05:57 PM

Quote:

Originally Posted by arnoneh

That's what I meant when I said I didn't notice the temp peg during the 10 mile drive....I didn't notice the gauge. Prior to today it has always run at normal temp, although I don't normally drive it since it is my wife's car. -harv

Well, without any knowledge of what the engine did prior to the overheat, my advice is to simply fill it with coolant while cold and take it for a drive.

Observe the gauge this time.........and note what it does. Don't stray too far from home and don't drive it if the gauge gets to 115°C. In fact, better head home if the gauge crosses the 100°C. mark. You won't have much time.

arnoneh · #9 08-17-2007, 06:08 PM

yup, I'll be doing that in a few hrs when I get off work. thanks

sixto · #10 08-17-2007, 07:05 PM

Quote:

Originally Posted by arnoneh

What about the water pump...how do I test that?

If the temp gauge shows normal temps, the water pump is probably okay. There's no way the water pump can generate enough pressure to push fluid past the reservoir cap.

Have you done the residual coolant pressure test?

Sixto
87 300D

babymog · #11 08-17-2007, 07:07 PM

Also check the top radiator hose with the engine warmed up, it should be hot. Turn the heater to full hot while driving and ensure there is water flow to/through the heater core.

arnoneh · #12 08-17-2007, 07:24 PM

I'll do all these recommended steps tonight....but, uh, how do I do a "residual coolant pressure test"? I couldn't find anything about this other than some guy on a volvo site that said he made his own.

Thanks -harv

sixto · #13 08-17-2007, 07:34 PM

Go home, have a good dinner, get a good night's rest, wake up, pop the hood, press the upper radiator hose. It shouldn't feel like the coolant is under pressure. Check the radiator hose of another car for comparison.

Sixto
87 300D

Brian Carlton · #14 08-17-2007, 07:36 PM

Quote:

Originally Posted by sixto

Go home, have a good dinner, get a good night's rest, wake up, pop the hood, press the upper radiator hose. It shouldn't feel like the coolant is under pressure. Check the radiator hose of another car for comparison.

Sixto
87 300D

If in doubt..........open the expansion tank by removing the cap. If the upper hose is now much "softer" than it was before you opened the cap..........it doesn't bode well for the diagnosis.