Coolant temp spike?
 

A strange thing has started to happen on my 84 300D. Normally coolant temperature will run 90-95C stop-n-go, highway, etc. Occasionally when pulling a long hill at highway speeds temps will get to 100C or maybe a needle width past. If I fill the coolant to the "full" line which I assume is that little line about a 1/2" above the seam in the plastic coolant reservoir it will slowly puke it out the overflow line over a week or so until the coolant level stabilizes just below the seam in the tank. Thats the way it has always run and I just figure it to be idiosyncratic to the car. Heres the strange part: Well, now at the bottom of a highway offramp if entering into stop-n-go traffic the gauge will shoot up to 105-110C and stay there for a few minutes then return to 90-95C. Same thing happens if I hold the transmission in S to pull a long hill at 35-45mph. I flushed the system last year, new T-stat and cap. I am thinking either the radiator is clogged or the fan clutch is inoperative. Any ideas? RT

You need to inspect the rad cap, fan clutch, and radiator to make sure they are all in proper working order. If so, what you describe *could* be due to a failing head gasket, which can cause erratic (and rapid) temperature swings. The good news is your iron head probably is NOT cracked. :p :p

Something is wrong, unless you were driving in the hot desert (in Nevada or nearby) so I think you better dig deeper and check the water pump or replace it. It could be all eaten up like Dave's in his W124 was (Dave, are pictures still available of that horrible impeller?) Or maybe the flush was not sufficient to clear the passageways in the radiator.

My W123's only hit 95+ on hot summer days after a drive in stop-n-go traffic with the AC on or up long hills.
Days like we have here (in the 60's) it is hard to get my OM617's over 85 - 90 degrees even if I drag race.
The W124 is a different story, mine runs hotter under similar conditions even with all new everything (pump, hoses, radiator, etc)
Oh yes, don't rule out a bad thermostat!
Dieseldiehard
1971 220 (gas) 4-spd manual 106441
1979 300TD w/ ’85 turbo engine 295530
1983 300D 243280
1985 300TD 217300
1987 300D 258230

Search this forum for "burping the cooling system". Although I have never had that problem, it seems to be fairly common from what I have read here. Worth a try at least.

I've never had to burp my W1213's just fill the block using the heater hose to the head, till it overflows out of the expansion tank, then replace the "S" shaped hose to the pipe on the firewall. Then top it up after the heater is run when the thermostat opens.
OTOH, W124 have a tendency to gurgle in the heater core if not burped.

sounds lke a fan clutch
 

If I was a betting man I would bet on your fan clutch-when you start your car cold build your RPMs gradually to 2000 RPM and listen for the fan "roar"-I bet your clutch fluid has leaked out. I just refilled mine with the Toyota 6000 CST silicone oil ($16 from your local Toyota dealer) and it made a huge difference with just one tiny bottle. If your radiator was plugged I think you would see high temps at extended hiway speeds(and not just uphill).

I'm betting on a cracked coolant tank -- they fail across the seam that goes through the cap fitting, and it will act exactly as if you had a bad cap (slow coolant loss, temp spikes at the end of highway runs, etc).

I also suspect you have a bad visco clutch -- refill or replace.

If the system holds pressure (pressure test it), get a new radiator, it's about plugged, and the worst spot will be right in front of the fan.

Peter

Read my recent post about oil analysis pointing to a blown head gasket / cracked head.

http://www.peachparts.com/shopforum/diesel-discussion/106069-oil-analysis-result.html

Your symptoms don't really sound like this, but, for ten bucks you can get an ananysis which will confirm if coolant or its components are present in the oil. At least then you could rule that possibility out pretty cheaply. You might learn some other things in the process.

It wasn't on my car, it was a co-workers. We suspect it had plain water in the system for a period of time to cause this amount of rust:

http://www.meimann.com/images/mercedes/W124_stuff/pump_housing.jpg

http://www.meimann.com/images/mercedes/W124_stuff/pump_impeller1.jpg

http://www.meimann.com/images/mercedes/W124_stuff/pump_impeller2.jpg

:cool:

Thanks for all the info so far. The waterpump was new 1 year ago. The plastic tank is not cracked. The coolant is pushed out the overflow/boilover tube until the coolant level drops down to just below the seam in the plastic tank. No way the tank is leaking, it would be pretty obvious. This strange habit of puking up coolant until it gets down to the "normal" level is the most perplexing part of this. How exactly do I test for a blown/leaking headgasket to rule that out for sure? Why would there be coolant in the oil? Blowby to the combustion chamber? I would think there would more likely be evidence of combustion gases in the coolant? The car doesn't use any coolant once it has puked out enough to get down to the "normal" range. "Normal" for this car anyway. If the radiator is plugged wouldn't it heat up running hard down the highway? I will pull the radiator and have it flow tested. Thanks all, RT

Bad head gasket will leave the cooling system pressurized cold, so will a cracked head. If the upper radiator hose is hard first think in the morning, suspect a combustion leak.

It will blow "excess" coolant out when there is too much in there. On my cars, "full" is the seam for the top cover of the tank, a couple inches down. More than that will probably over-fill the tank and spill out the overflow.

I'd also pressure test it -- it's possible you have a small leak somewhere that prevents it pressurizing properly, and this will do cause all the noted behaviors. Look for a gouge in the sealing surface in the tank neck, too!

Yes, a clogged rad should make it run too hot under load, but that is exactly what you describe, isn't it? Just running down the highway isn't that much of a load unless you drive with your foot to the floor all the time, but climbing hills is!

Running 95C in traffic is usually a bad visco clutch and resultant poor cooling airflow, but a bad radiator will do the same thing. Easy check -- get it warm and look for a cold spot on the rad, usually rigth in front of the fan.

Peter

RT,
If you have a head / head gasket problem where your coolant is being dumped, then the coolant will quickly change from green or orange to black.
This is due to the combustion gasses being released into the coolant.
Pretty easy to see.
Also check:
Cold engine pressure in rad hoses
Radiator pressure holding test (pump up and check for leaks).
Radiator core check (IR video camera is effective in this test)
Fan clutch check. (when temp is >90'C mech fan should "roar" as engine is revved)
Electric fan check. Should be running if temp is >95'C

Hopefully an inexpensive repair will eventiuate.
Best wishes,
Tony

erratic remp guage
 

Rob,
My '85...the Black Bomber has just hit 225,000. This one runs slightly cooler than my wife's 1982 300Sd.
The Black Bomber runs like a top. It will ALWAYS "PUKE OUT SOME ANTIFREEZE" from the expansion tank.....and LIKES to run at around the seam level.
All of your thoughts are right on the money....However, remember the keep it simple stupid thought process.....It IS possible that your NEW thermostat MAY be the culprit.....same with the radiator cap....Are your symptoms the SAME as when they were replaced?
Have you ensured that the ELECTRICAL contacts and connector for the temp guage are clean........easy to make sure of......Get another SENDING UNIT and TEMP GUAGE assy from a boneyard and rig them up to compare. I bet that you MAY find that the sending unit may be off.........
I would just connect another bguage to the sending unit INSIDE of the engine compartment on tha side of the road once the high temp occurs. Just to COMPARE readings.
I hope that this helps in your thought process.
Best wishes always,
spo out :cool:

Thanks for the additional replies. The cooling system used to hold pressure but that seems to have gone away with different radiator caps. About a year ago I installed a new water pump and tried 3 different thermostats and radiator caps. Going to a cooler t-stat didn't change the temp reading on the gauge so I began to think of the temp gauge as a general indicator not a precision device to be truly believed. The current T-stat is 78*C rated and I am running a 7psi cap. Why the low pressure? Why not? Less stress on a 20yrd old cooling system at 7psi. Understand that these changes occured a year ago and the cooling system has been trouble-free until now. I will take a good hard look at the radiator and fan clutch. Thank you all again, RT

rwthomas1

Did you solve this? I am battling the same deamon now. My gauge runs at 95, then spikes to 105ish, erratic, then settles back down to 95. I bought an IR temp gun and have taken reading many., many times. (done all the usual, fluch, clean, replace t-stat-80 degree)

Nowhere on the block, radiator, hoses can I get a reading of more than 75...so, I know my cooling system is working just fine. So, I had to focus on the sending unit to the guage portion.


I replaced the sending unit, no change. All that is left is the Potentiometer and the gauge (ground or connection or broken gauge). These are more diffiucult as this requires removing the dash cluster, I have NO idea how to do this.

If you have made progress, can you let me know.

AC