Overheating, '85 300D

[siredmund]

85 300D Overheats, but shows no signs of steam in the exhaust or water in the oil. Starts & runs well and has good oil pressure. No sign of exhaust gas bubbles in coolant resevoir. Former owner said he drove it about 100 miles with a broken generator pulley, he replaced the pulley, but now it overheats, has no electricity, but runs fine. The generator and water pump seem to be turning OK. Water boils out of resevoir after about 20 min of running.
Will appreciate any advice as to how i can tell if the head gasket is blown or some other cause, and if there is relatively minor damage to the gasket, could an additive like "Mendtite" be a temporary/semi-permanent fix?

Forgive me if this has been covered before, i did search for about 1/2 hr.

sir edmund the green

[bill murrow]

To check for blown head gasket start the car and then take the radiator cap off. Look for bubbles forming in the coolant or the coolant level rising up and down.

I would fix it right. Replace the gasket if that is the culprit.

First I would look for simple stuff. Your thermostat ok? Maybe pull that out and change it.

Cheers,

Bill

[siredmund]

Thanks for the response. Mine has no radiator cap, but checked the coolant resevoir, and there were no bubbles, but water oozed out gradually, presumably from thermal expansion of the water in the rest of the cooling system. Could the exhasust gas bubbles be hiding somewhere since i can't look directly into the radiator?

[stcbenz83]

Originally Posted by siredmund

Thanks for the response. Mine has no radiator cap, but checked the coolant resevoir, and there were no bubbles, but water oozed out gradually, presumably from thermal expansion of the water in the rest of the cooling system. Could the exhasust gas bubbles be hiding somewhere since i can't look directly into the radiator?

no radiator cap???

[bill murrow]

Originally Posted by stcbenz83

no radiator cap???

Yup....my '85 TD has no cap on the radiator itself, only a cap on the resvoir.

I'd change the thermostat. make sure you get one of the "no fault" t-stats. Its one that remains open when it goes bad thus your car cannot overheat.

While you're at it, might as well flush and change coolant too. Can't hurt and most likely needs it.

Cheers,

Bill

[veg_hed_300d]

I had some overheating issues on my 82 300d and this link covered a lot... hope it helps...


http://www.dieselgiant.com/thermosta...ntandmodif.htm

[tangofox007]

Originally Posted by siredmund

Former owner said he drove it about 100 miles with a broken generator pulley
sir edmund the green

If a "broken generator pulley" means that the drive belts were inoperative, then the car was driven 100 miles without a working water pump or fan. That can't be anything but bad news.
Could you could define "broken generator pulley" a bit more precisely?

[siredmund]

The former owner didn't define it exactly, but that it meant the water pump was not operating for 100 miles. He replaced the pulley & alternator, but now there is no electricity and it overheats when driven, even tho the belt and pullies seem to be turning fine. I guess my main question is, If there is no steam in the exhaust, water in the oil, oil in the coolant, and no bubbles coming out of the RESEVOIR (no radiator cap) could it mean that the head gasket is NOT BLOWN, or maybe only slightly damaged and fixable with additive. But on the other hand, since it was driven 100 mi (plus i drove it another 40 on a cold winter night when i bought it), could the head gasket be anything but blown??

thanx,
ed

[barry123400]

It is hard to believe someone would do that. I guess if it did boil over and get too hot perhaps no damage was done. Diesels will tolerate more sometimes. You should ask him if it was boiling over on that 100 mile drive. I get the impression the weather was very cold. He was no doubt dumping heat through the heater core. The question is was it enough? Did he have core circulation? Anyways start with the thermostat as people have suggested. What I am kind of suspicious of is a thermal stress induced crack somewhere perhaps. Especially if he kept pouring cold water into a really hot engine. You might disable one cylinder at a time and take it for a drive if the thermostat does not help. That should give some indication of a cylinder that is producing too much transfer of heat to the cooling system with a crack or gasket problem. Even though there are no apparent bubbles at idle. They may be there at speed. In fact you may be able to do the test at idle if it seems to really generate excess heat fast at idle. Also check the archives to determine if the fan is functioning properly. Just a few random thoughts even if not particularily pleasing. Hope it turns out as something simple.

[stephenson]

My bet would be a blown waterpump seal - could, of course, be the head gasket .... if you are doing your own work, the cost of the pump, new tstat, and coolant is relatively minor compared to ANYTHING related to replacing the head gasket and associated head work ... do the electric fans work? Does it have a clutched fan - is it locking up as it heats up?

[85chedeng300D]

Originally Posted by siredmund

The former owner didn't define it exactly, but that it meant the water pump was not operating for 100 miles. He replaced the pulley & alternator, but now there is no electricity and it overheats when driven, even tho the belt and pullies seem to be turning fine. I guess my main question is, If there is no steam in the exhaust, water in the oil, oil in the coolant, and no bubbles coming out of the RESEVOIR (no radiator cap) could it mean that the head gasket is NOT BLOWN, or maybe only slightly damaged and fixable with additive. But on the other hand, since it was driven 100 mi (plus i drove it another 40 on a cold winter night when i bought it), could the head gasket be anything but blown??

thanx,
ed

Is it really possible to do that on a Mercedes??? I know that 300Ds has an electric/auxillary water pump, but does it help in the water circulation of the engine cooling system??? i thought its only for the heater/climate control system???

[siredmund]

Hi folks, thanks for all who have offered advice. I FINALLY got around to pulling the thermostat, and put it in water, heated it to a boil, and it did NOTHING, so i put the cover back w/o the thermostat, and let it idle for 45 minutes, and it very gradually heated up to about 72 C. (on the temmp guage), and the water in the resevoir was at 65 C. (cooking thermometer). I noticed a few small bubbles coming up thru the fluid in the resevoir after it had been idling 45 min. The radiator seemed uniformly warm, but not hot.

QUESTION: Are these temps normal for no thermostat (ambient air temp was about 82F)? Do a few small bubbles mean minor head gasket damage? Where's the best place to order the right thermostat cheaply?

Thanks!

ed

[siredmund]

Hi folx, me again, well, i took it for a spin with no thermostat. 6 miles mostly up hill, and back, weather, 94 F It took a while, but mostly hoovered at 80C, a crack above or below. Same on the return trip, mostly downhill. Ran Ok, remained at 4 atmoshperes of oil pressure.

Question: Is it worth getting a thermostat, or if the car is that hot with no thermostat, does it mean i have a blown headgasket or worse??


RSVP,

sir edmund

[dieseldiehard]

I would replace it with a good thermostat. The long slow warmup is hard on the engine. A Diesel needs to get up to temp as soon as possible especially when the weather gets cold. You need to keep the cap on it too! And run approx 45 or 50% coolant mix (antifreeze to water ratio).
If it runs much over 85 C under normal driving conditions then you have other problems, like the radiator, water pump or ???

[SD Blue]

These engines use a bypass system for coolant. Without the restriction of the thermostat, cooling is actually hindered since there is reduced flow through the radiator.