87 300TD Overheating

[87Bielenberg]

Whats up guys. I just bought an 87 300TD Turbodiesel Estate with only 150k and 3 owners the second of whom was a Benz mechanic. Beautiful car and it gets me around town without any major issues. It does have a few glitches though which I want to resolve the most major of which is overheating because I want to take it on road trips and use it as a travel car. I am not very knowledgeable about these cars but I really want to learn and get it up to spec. Any advice would be greatly appreciated. Thanks.
PROBLEMS:
1. Overheats when climbing hills on the highway. Driving in town the temp will stay at 90 C and it will usually stay at 90 C even going fast on the highway. When climbing hills going fast on the highway though the temp starts to slowly climb. If I turn the heater blower on full blast this usually drops it down and helps it stay at 90-100 for a while. Eventually though the temp gauge starts climbing again and I have to pull over. The coolant reservoir will be pressed full and boiling and it will usually be leaking out behind the front passenger side wheel which is where the overflow tank drain is I guess. And this happens even when I am not going very fast and in very cold weather. It has a bastard Nissan radiator fan and apparently the original Merc fan works better, but this can’t be the only issue.
2. Rough Startup and starting idle. Revs high and sputters for a few minutes. Valves too tight? Needs valve adjustment? This is during cold temp in Montana winter.

3. Delayed/Hard shift from 1st to 2nd. Jerks. All other gears are fine. Surges at low speed or idle. In 1st gear or reverse rolling slowly or at a stop the engine will rev up to 10 rpm if it is just idling at 5. Might kick up twice while sitting at a red light. Going slowly in reverse this happens a lot.
4. When slowing to a stop the ABS comes on, you can feel it in the brake pedal and it makes its noise.

[kerry]

Ohhhh boy. I hate to be the bearer of bad news but start doing some searching on 87TD's overheating, failed headgaskets, #14 heads etc.

[ah-kay]

Welcome to the Forum. Kerry, don't scare the daylight out of our new member.

I am a home mechanic but I can share some experience with you on item 1. No idea on tranny issues. Others can chime in.

1) You probably have a small leak in Head Gasket. I put up with the problem in my SDL with #14 head for 55K miles. Now is at 331K. I have to add a quart of coolant every 1-2 week. so it is not the end of the world. This is what I did.
a) Change out the thermostat to activate the aux fan from 115C to 110C ( a red one ).
b) Hard wire the Aux fan to high speed with a switch. Turn it on when I have a long climb just as a precaution. It saved my ass and the car when we traveled thru Death Valley and the car over-heated.
c) I fixed the HG using Blue Devil seal. I have not added any coolant for the last 6 months or about 6K miles.
d) I have not been to Death Valley since I fixed the HG so the jury is still out.

2) There is no valves to adjust for the om603. It is self adjusting. Rough start could be due to Glow Plug or fuel injector issues.

4) ABS light could be caused by Over Voltage Protection Relay.

It is unusual for the om603 with 150K to have so many issues.

Good luck.

[vstech]

yeah... the original head on these cars were not forgiving...
on the plus side, the Nissens radiator is actually superior to the Bher...
the valves are not adjustable on this motor...
it could be a plugged cat in the exhaust... any chance the original "footbal" trap ox is sitting on top of your turbo? if so, you may be in luck, as MB has a recall campaign on it...

[87Bielenberg]

Thanks for the helpful imput guys. Lets assume the worst and say i do have a leaking head gasket. What now ? How much to replace it and is it worth it on this otherwise stunning car? I dont really want to go cheapo and use sealer... The ABS light doesnt come on but I can feel it in the pedal and its annoying.

Is it a certain temp that kicks in the aux fan or is it the speed?

[FryBird]

I had same exact overheating problem, replaced the main (belt driven) fan clutch, problem solved,

[barry123400]

Read in the archives how to check the fluid coupled fan clutch. It is probably the cheapest candidate in the list of possibilities. Besides pressure testing the radiator cap that is.

Also look up the hard coolant hose test on the 603. Basically the upper radiator hose should not be hard eight hours after using the car. This test is only valid if the system is capable of holding pressure of course. Last but not least post the head casting number.

You cannot mentally treat any issue that looks like a head gasket on these engines as it positivly being the issue. Far too many heads have developed cracks to do that. So on this engine a head gasket is far from the worse senario unfortunatly.

Mercedes continually tried to improve the heads over the span of production of that engine several times. The number fourteen head that was the normal one back when your engine was produced was the most problamatic one for cracking. They like to crack between their valve seats.

If cracked the only sensible situation is to locate a good used newer head candidate for it. Not cheap usually unless you are lucky. It also cannot be warped as there is no allowance basically for material removal to resurface it.

It is also almost reasonable to assume that on occassion it might be a head gasket. If a person where prone to gamble in my opinion it is a bad odds situation though.

If mercedes had just put a cast iron head on that engine instead of aluminium. Or initially got the head casting right in aluminum it might have been a worldbeater almost bulletproof engine for the time.

Since the car was at one point owned by a mercedes mechanic. The call back conversion for the exhaust has probably been done. Yet it never hurts to have a look as sellers with either misinformation or outright lying have been known to exist.

They unfortunatly are not an endangered specis. In fact if we were allowed to shoot them there would be a sizeable drop in the population I imagine.

[vstech]

you can safely ignore the cap as the culprit for the overheating... my pressure tank leaks all the time, and the motor never overheats, because everything else in the cooling system is new... (I know I know, I gotta fix the tank) my point is, the coolant will experience hot spots, but will not overheat solely due to a bad cap. there is something else causing the heat to build up in the coolant. either thermostat, the water pump, the fan clutch, or the radiator...
period.
also know, that temps above 90, but below 100 are perfectly normal.

[Brian Carlton]

Originally Posted by 87Bielenberg

Thanks for the helpful imput guys. Lets assume the worst and say i do have a leaking head gasket.

Let's assume nothing.

Let's also ignore all of the "possibilities" that exist because they are simply a shotgun approach to the problem. Without data, you could have just about anything causing your temperature issues.

Do you wish to do some investigation to attempt to find the source of the problem or simply forge on without the data?

[theref]

I have had the cracked head issue in spades-including a -22 but that does not mean that this is the case here. The radiator is also a suspect. Like gsxr (Dave) I have come to the position that radiators should be changed at 5-6 year intervals. (Although I never heard that Nissen was better than Behr with the reinforced neck.) The aux fan switch/sensor is another possible suspect and should also be changed periodically. Just because the second owner was supposedly a MB tech says nothing about the third owner. Unless it is examined by a knowledgeable viewer, the trap oxidizer could still be installed. We don't even know if the water pump/thermostat are in working order. Can't just go by reputation of this model all the time. And an overnight coolant system pressure check can reveal hydrolocking as an indicator of a head problem.

[Jeremy5848]

Brian is correct -- you could spend a lot of money making repairs that would end up doing nothing for the problems you describe. The overheating problem is likely the only potentially serious one, the others are nuisances. DO NOT continue to drive the car if it overheats and you cannot bring the temperature down (by turning off a/c, turning on the heater, etc.). The engine will be fine at 100C and even as high as 110C but don't let it get any hotter. The #14 head is a known weak spot but that doesn't mean you have a bad head. My '87 300D Turbo had a damaged #14 head but never overheated so don't make any assumptions.

There are many links in the cooling chain and all must be working for the car to perform normally. The clutch on the belt-driven fan is heat-activated. With the engine idling, use the STOP lever to kill the engine. The fan should stop immediately. If it pinwheels for more than a second or two after the engine stops then the clutch is shot. Replace it. The 603 had a metal fan from the factory and the replacement clutch is quite expensive. You can retrofit the 606 plastic fan and clutch for a considerable savings; it is almost identical to the 603 fan and requires no modification.

The 2-speed electric fan is switched on by the a/c system (runs in low speed) and by a sensor in the head (3 pins, near the upper radiator hose) in high speed. Short the terminals on the switch near the a/c dryer and the fan should run in low speed (key on, engine not running). If you can't get the electric fan to run it should be replaced. However, the fan itself is less likely to fail than the switches and relays that power it. Replacing the switch in the a/c circuit requires emptying and recharging the a/c, a potentially expensive job. Replacing the switch in the head is much easier; regardless, the stock switch (has either a gray or a light blue plastic top) switches at too high temperature and should be replaced with one that switches at a lower temperature. The one with the red top, Mercedes p/n 006-545-42-24, switches on the electric fan at 100C and switches off the a/c at 110C.

Other cooling system issues to consider are the radiator, water pump, and thermostat. Do you have any idea whether these things are original? What kind of coolant does the car have and when was it last changed? Check all of these things and we can go from there.

Jeremy

[vstech]

are you certain the temp switch in the reciever requires the refrigerant to be drained in order to change? I was under the impression it was merely attached, not intruding into the freon circuit...

[Jeremy5848]

Originally Posted by vstech

are you certain the temp switch in the reciever requires the refrigerant to be drained in order to change? I was under the impression it was merely attached, not intruding into the freon circuit...

It seems to me that the switch in one of my cars was bad and was replaced by my mechanic (whom I trust to know what he's doing) and the refrigerant had to be removed and replaced. But I'd be happy to be wrong, it would save a lot of money next time!

Jeremy

[ah-kay]

Some earlier aux fan switch is based on temp, some is based on pressure. I am not sure when is the transition model.

Temp based - no evacuation of freon required.
Press based - evacuation.

[Jeremy5848]

Originally Posted by ah-kay

Some earlier aux fan switch is based on temp, some is based on pressure. I am not sure when is the transition model.

Temp based - no evacuation of freon required.
Press based - evacuation.

My [paper] FSM "Service Manual / Automatic Climate Control / Model 124," published in 1989, says that the switch in the refrigerant line is pressure-based: "On at 20 bar / Off at 15 bar."

EDIT: The CD-ROM version of FSM gives the same information for the 1995 E300D so it would seem that all 124s use a pressure switch in the refrigerant to turn the aux fan on in low speed. Perhaps a temperature-sensitive switch was used in some other models.

Jeremy