1987 300TD Overheating
 

About 2 weeks ago i was coming home from work around 6am doing about 65-70mph with outside temp around 55*F on a slight up hill when i noticed my temp gauge start going up. i caught it on the line right above 80*C (not sure what temp that is) and turned the heater on full. temp started dropping and sat right above 80*C.

fast forward to now, takes about 30min at idle for car to get to the line above 80*C. if i accel the pedal for a while temp starts to drop. if i'am on the freeway on a flat surface going between 40-60mph car runs perfect at about 80*C. if i go above 65mph or hit a hill temp start going up. if i get off freeway and hit stop and go traffic, temp climbs up again. so far i have not lost coolant and have not let it get passed the line above 80*C and if it does i turn the heater on (never let it get close to the 120*C). i also noticed that the front Aux fan does not turn on even when direct connection. before this car ran at around 80*C all the time with no issues.

just wanted find out were i should start first since you guys have more experience with this problem on the om603 with a #14 head. i hope its not the worst news:(:

No need to jump to such terrible conclusions just yet. Sounds like you are familiar with the issues regarding this engine design and head casting.

The temperature rise is obviously dependent on load, as you have described. This implies higher fueling rates and greater cylinder pressures. These demand higher rates of cooling from your system. Any of the system's elements may be suspect, to a degree.

It is quite possible that some things may be failing that are easily fixed. (easy is a relative term, I know)

-thermostat (it can happen and cause this, but somewhat unlikely. However it is cheap and therefore worth the effort)

-Head gasket

-Obstructed radiator

-bad fan clutch (highly unlikely)


-and you are aware of the worst outcome, aren't you?

am actually afraid of the worst outcome:P. the coolant is clean cause i drained some the other day but there is some light brown residue inside the reservoir tank. not sure if that makes a difference. could there be major damage even though it never got extremely hot? and what is the temp line between 80*C & 120*C? my buddy gave me an extra auto parts store T-stat that am thinking of drilling 4 hole and see how that turns out. any other suggestions? dont want to start blowing money, hard times:D

If you want to modify the t-stat in some way and test it.... remove it completely and run the car without it as long as you do not have any long , steep ascends.

brown residue... not sure, thats kinda ambiguous to me. But might indicate the maintenance history of the coolant in the past.

Definitely the cheap stuff first.

I am almost certain that line is 100*C

the major engine damage seems incredibly unlikely under 100*C.... slightly over it on a repetitive basis and I wouldn't put my word behind any guesses.

am going to try the t-stat first and see what happens. my wife has been driving around town on the street (not the freeway) most of the day and has not got hot so far, stays around 80*C. i'll check it out when she gets home this afternoon.

first thing you should do is get the car up to temp. (*the middle line is 100C) then immediately pull over, and shut down. pop the hood, and see if the fan spins easily, or it's stiff. if easy, your fan clutch is failing.
next as a temp measure, get a good solid jumper wire, and place it between the two phillips screws on the large resistor behind the driver's headlight.
that'll allow the aux fan to engage at full speed when called on.
lemme guess, 134a freon in your a/c?
this is what mine was doing, and I found these issues.
I have a 93 parts car, so I'm gonna pull several parts and upgrade my TD!

my wife just got home so i told her to leave the car running. i opened the radiator cap expecting coolant to burst out but nothing happened, just some steam! i pressed the upper radiator hose with my hand and it was not too hard and hot. i also notice the coolant moving around the Resv. tank every time i pressed it. the lower one was not as hot and a bit softer. temp on car was about 90*C (just below the middle line).

Any ideas?

First off, you have a bad cap. the coolant should have been sitting at 22psi!!!
NEVER TAKE THE CAP OFF THIS CAR AT TEMP!!! VERY VERY DANGEROUS!
did the fan spin easy?

sorry, i missed your previous post about the fan clutch tip. the car's A/C has not been working since i owned it. tried connecting the Aux fan to direct power and it didnt spin at all. also the Cap was the first thing i changed about a week ago. am going to drive it around and check the fan clutch.

if your cap is new (*MB 140 new, not stant 13psi new...) I'd look at the small hose that goes accross the front of the radiator. where it connects to the head above the serp tensioner spring. I bet it's leaking pressure here.

well i went ahead and did the fan clutch test and when i opened the hood the fan was just about to stop spinning, in other words "its very loose". would a bad fan clutch cause it to over heat at freeway speeds or just in stop and go traffic? i found some beige build up inside the t-stat housing against the pipe. it sort of crumbled when i gave it pressure. now am thinking it might be the radiator thats clog. i also tested the t-stat (factory) in hot water and it worked good.

anybody know of a good affordable place to buy a radiator and/or fan clutch? :D. i heard you cant have these cleaned out or rebuild (both).

The fan clutch can be re-filled, there is a thread here somewhere (possibly in the DIYs).

Start at the beginning. You drove your car, and it went to the 100C line, that's no big deal. Shouldn't run that warm on the freeway, but not dangerous, ... so what could be causing it?

First, if there are no other symptoms of cooling system problems, consider replacing the temp-sensor. It is the green (or blue) 3-wire sensor just forward of the #1 injector, it turns the aux-fan on (at 105C?) directly, and feeds temp info to your gauge. It might be bad and throwing your gauge off. The new one is a lower temp cut-in for the fan so that's all good, and IIRC it's only around $20 or so new on-line.

The aux fan. Should run if you power it directly, if it didn't then the fan is one of your problems. Does the electric (aux) fan rotate freely by hand? Powering the fan resistor should give you low speed on one side, high speed on the other. The Freon pressure turns it on low. High speed is run from the green (or blue) coolant temp sensor mentioned above, short across the two-wire connector to run the fan on high.

Next is the clutch fan. At that 100*C mark, rev the engine. Do you hear the roar of the fan? If not, then either your fan clutch is bad, or the temp gauge is reading high (covered above). The fan clutch should also be engaged cold, when you start the car in the morning, should roar on first start/rev of the engine. If not, it is bad. Also check for play in the fan clutch, if that sucker is bad they have a way of eating expensive radiators.
The clutch fan should keep the car below 100C (normal driving / normal temps), and without it you will see elevated temps. If the aux fans are working then it should come down when it hits 105C but the clutch fan is necessary even while driving as the aerodynamics of the 124 don't shove as much ram air through the radiator as the old days.

If these things are fine, check for hot and cold spots on the radiator. If it is hot in some areas and cool in others, likely there is a restriction in the radiator, bad thermostat, or bad water pump. Using the wrong coolant can eat the water pump so that's a possibility over the years. Generally the radiator shouldn't vary much in temp from one side to the other, significant temp variations indicate blocked tubes.

How many miles are on the car?

the car has 245K miles on it. the upper passenger side corner of the radiator seems warm, not hot like some other spots. i accel the car and didnt hear a roar. didnt seem to speed up either more like slow down every time (cant really tell). i can feel air with my hand at idle but stops when i accel. theres no play at the fan.

am going to look around and see if i can re-build the fan clutch (maybe someone has a link) if not am going to save some cash to buy a new clutch, radiator and probably a water pump:eek:

if you can rebuild it, post procedure in a thread!
mine's shot too. but I have a 602 in good shape to pull parts from.
if you can't rebuild it, the clutch for the 606 is less expensive and highly thought of.
my 602 has two 12" fans, instead of the single 16" fan... I wonder if it would be adequate to cool the car... two offers redundancy...

i like the idea of using the om606 fan clutch. is it from a 94-95 E 300? any other info on it? just want to make sure i dont buy the wrong one.