I've had a 1987 300SDL for... oh... almost 2.5 years now? The car has mileage: 250k, yeah. I dearly love this car, and have invested huge chunks of change into it time and time again. Transmission, front suspension rebuild, engine mounts, an oil pan (my bad), cosmetic details... when I bought this car I was expecting to pour ~$10k into price + fixes, and to basically have it not need any work after that. Well, I've poured that money in, but theres one thing I have not addressed, and this really should've been the first thing I looked at.

My car overheats going uphill. The cooling gauge stays around 95C during non-winter months, and when I go uphill, it starts slowly steadily rising. Its slow, but it doesnt seem to slow down as it heads into the red.

On the east coast, this would not be a problem. I, however, am in the rockies, and we have little but mountains.

What possible causes are there for this? Are there remedies? I love this car, am happy to pour money into fixes, but this is one of the rare issues where I dont know what if anything can be done. Is this symptomatic of all old diesel benz's? Is there anything to be done, or is it just an old tired engine?

I had a bad incident trying to get out of an offroad camp site 20 months ago, where I was so busy trying to get over a hill I didnt notice that I was drastically overheating. I'm a bit hazy on recalling the details, but something in the cooling loop blew a leak, and I had to feed it water until I got to the city. They replaced, amongst other things, the thermostat and the cooling loop impeller. Of all the things I'd suspect would be the cause of cooling issues, those two are are the top of my list. I'm tempted to take out the thermostat altogether: the work lost to constantly pumping coolant seems a worth sacrifice to possibly keeping it cool.

This is absolutely critical to me. This has been an issue with the car since I bought it, and I should've figured it out then, but for whatever reason I never have. If this is not a resolvable issue, I'll have to sell the car, even though I've already invested a ton of money under the assumption that I'll be driving it for another 150k-200k. What should I check, what can go wrong, what can I fix?

There is a local Benz shop I trust greatly, but in this particular issue I feel the need to reach out and figure out what I'm dealing with.

Thank you for your time and consideration,
rektide

The temperature will climb when the vehicle is under load. However, unless you're in 110° ambients, it shouldn't go over 105°C.

If it does, you've got two major possibilities:

1) The clutch fan is shot. Shut the vehicle down when it's quite hot. The fan should stop instantly. If it spins, change the clutch fan. The switch to the 606 fan clutch is recommended as a cost reduction.

2) The radiator is 20 years old and the fins are partially blocked. You can remove the radiator from the vehicle and spend a couple of hours with some condenser cleaner and an air compressor..........or just replace the radiator.

One or both of the above will be the likely culprit.

Thank you for your extremely prompt and exact reply,

The clutch fan was replaced when the cooling system blew. I believe it was partially faulty before the incident, and that it was replaced in the due process of "fixing everything" in the aftermath of the incident.

I've suspected the radiator might be the problem, but have been wanting on ways to check. Thank you for your suggestions for possible DIY improvements. I'm a bit terrified to think of what an actual replacement job might cost; I understand this is one of the "pricey" items junkyards immediately pull out of most cars. Most troubling is the idea of going in to a $1400 or $1600 repair job not knowing whether its going to help; I think thats been a large part of the reason I havent pushed this matter sooner.

You absolutely do not want a used radiator. You already have one of those.

Get a brand new Behr..........$437.30............and do it yourself in about two hours maximum...........DONE.

Could a cracked head also cause it to run hot? We all know how infamous these engines are prone to having cracked heads.

__________________
DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

It could, but it probably wouldn't be limited to heavy loads and it wouldn't be operating at normal temperatures at moderate ambients.

A quick oil analysis would confirm or deny any glycol in the coolant. It might be worth the $20. for the peace of mind.

Isn't there the upper radiator test that can be done where you wait overnight to see if it has pressure or not?

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

Just squeeze the upper hose in the morning. If it's hard as a rock..........you've got issues..........

That's how my 87 300D was. It would also run hot in traffic and driving up hills.
Sorry for the hi-jack.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

Make sure the coolant is changed too, it doesn't last forever MB recommends changing it every 2 years, thats 24 months so you're due.

NOW PROMISE PROMISE PROMISE NEVER TO LET A COOLING ISSUE LINGER THIS LONG AGAIN.
I dunno where you got the idea this would be a $1500 repair, these cars aren't made of gold... New radiator, maybe a citric acid flush through the cooling system and you should be all set.

You don't want to run without a thermostat for 2 reasons:
#1. This is a diesel engine, if it doesn't get up to temp it won't run well. The engine relies on heat for compression ignition to work correctly.

#B. Your car will always overheat. Thats right and this is something folks used to American cars have a hard time handing, the thermostat opening closes off the loop back passage in the head, if the thermostat isn't present the coolant will take the path of least resistance and stay in the head. The thing that fakes some people out is that from a cold start the car will run fine for awhile but if you get it warm, shut it off and restart, it'll overheat... BTDT.

The thermostat is there for a reason, I hate it when people pull the thermostat rather than fixing the problem.

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Sadly Benz-less

I agree with Brian, sounds like you have a very old cooling system. In Hell here, I don't get much past about 90-95°C with the 606 clutch/fan, new radiator, proper coolant. I think I've hit 100°C a few times when speeding about on the freeway in the summer.

You guys just need to break down and purchase a new radiator, fan, fan clutch.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Mine exhibits these same symptoms pulling the 2,000 feet up the mountain to school and the radiator's new within the last 3 years (when I crunched the oak tree the first winter we had the car), fan/clutch within the last year (converted to 606 parts).

I can *usually* make mine stop trying to overheat (I certainly never let it hit the red before I do something) by turning the air conditioner off. The spare horsepower this frees up seems to help the problem... the temp then just stops close to where it had climbed to (usually 115-117 degrees) and stays put until I give the car a break again. Turn the air on, and it's pretty much an instant increase on the temp gauge. Have never let it keep climbing to see where it'll stop but it was 115 and climbing when I killed the air last time.

Our Explorer and F-250 both had/have (we don't have the Explorer anymore) aftermarket radiators that had an increased cooling capacity compared to the factory standard original (more cooling loops within the radiator or something, I'm not sure). These extra-capacity radiators were intended for people that did heavy towing and pulling, and it sure showed on the average cruising temperature.

Anybody come out with something like this for the SDL yet? It's certainly a good idea, if you ask me, if somebody could figure out how to do it.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Well how many of you guys clean the AC condenser???

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Can someone elaborate on the radiator hose test? Do I have to do anything the day before? What conditions is the test testing for, eg what does it indicate?

I've had new coolant put in, and it did offer significant improvement. I also do not use the AC.

You just need to drive it and park it.

You're testing for pressure in the cooling system the next morning.

It might indicate that further testing is necessary to determine if you've got a failed head gasket or a cracked head.