i would do a flush befor i replace my radiator (i sure as heck dont want to pay $300+ for a radiator....) and my water pump is definaly working because the temp drops as soon i drive it or use the heater, probally its my fuel gov pin is set to the max, anyways i am going to replacethat pin and a radiatorflushso i keep on updating....

thx

 

eBay has some good buys (~$100) compared to what a mechanic would charge.

 

I have a 1983 300SD that was running hot, but not to the point of boiling over or stalling.

I had the thermostat and cooling tank replaced (there was a small leak in the cooling tank) along with a new pressure cap. The thermostat is a Mercedes OEM because the garage could only find one locally from the dealer that had the correct o-ring.

Now the thermostat does not seem to be opening at all: within 10 minutes of driving cooling system gets to the point where it's not boiling over but will if I loosen the pressure cap and there is a noticeable loss of power and increase in engine roughness. Took it back to the mechanic and he just shrugged and said maybe it has a blown head gasket or injector problem.

I also hear a clunking sound that appears to be coming from the radiator near the top hose.

I can see that it might need a new radiator. I can't see how that would affect the thermostat. Tomorrow I'm going to remove the new thermostat and see how it runs.

Without actually removing the head to look at it, and assuming its running with no thermostat, what symptoms should i look for in terms of ensuring the problem is in the cooling system and hasn't destroyed the engine in the meantime?

thanks
Andrew

1983 300SD with biodiesel modifications.

 

The biodiesel mods were done by the previous owner - it's a full mod with a separate biodiesel tank, fuel pump and filters. As far as I know only actual biodiesel was ever run in it. Personally I haven't run it on anything but the main diesel tank since the fuel in the biodiesel tank is old and needs to be drained. The previous owner has a trucking company and runs biodiesel in his fleet, so he has a good supplier / price for biodiesel.

I'm wondering, if it's the head gasket, why it was running pretty decently until a new thermostat / coolant tank was put in, and immediately started having serious issues? I suppose it could be coincidence, but it seems like a strange one.

Also, from what I've read on various forums, the head is particularly complex compared to one from a gasoline engine (the only time I've done head repairs were on a very simple gasoline engine from an 84 Skoda). A number of people seemed to feel if there are head problems it's best to just replace the whole engine. Thoughts?

thanks
Andrew

1983 300SD with biodiesel mods.

 

Oh, forgot to mention, I had the cooling system pressure tested and it came out fine, a sniffer didn't detect anything either. It still may be the head gasket but that would indicate a small leak or a leak that gets worse under load, correct?

Andrew

 

Last thing I forgot, the lower hose stays cold. The upper hose (to the top of the radiator) is where the heat builds quickly.

Is it worthwhile looking at putting in a complete remanufactured head assembly rather than screwing around with the head gasket? It costs a fair bit more but I don't want to continually disassemble the engine to keep fixing it, or worse wreck the rest of it due to a mistake with the gasket.

thanks
Andrew

 

I did the test you indicated. Before running it, removing the pressure cap let out a barely audible gasp of pressure. After running it around the neighbourhood for a few minutes and stopping it, the pressure gasp was the same as prior to running it, i.e. barely audible but there. I tested it first with the heat on, then repeated it with the switch moved all the way to full a/c, same result. The temperature gauge hadn't budged in about 5 minutes of driving from its lowest mark.

The pressure really starts to build when driving under load with the temperature gauge hovering around 100C. The hottest I've let it get to was just over that, and after stopping it the temp gauge continued to rise to about 115C, at that point the overflow reservoir did boil over.

thanks
Andrew

 

Turns out the mechanic at the shop put the thermostat in the wrong way. Might have been a small leak in the head gasket before but I think it's completely gone now.

Any thoughts on having it repaired vs buying a remanufactured head?

thanks
Andrew

 

Have the head checked for cracks and warping, and make your decision from there.

 

So I've had it at a diesel shop where they know the model pretty well, and after 4 days they're stumped.

The thermostat that was put in the wrong way warped and was sticking, replaced it and it takes longer to overheat, but still does eventually.

Coolant is barely moving through the system, even with the thermostat open, so took off water pump to check blades, they're fine.

System pressure tests fine, runs fine (until it gets hot), no combustion gases in the cooling system, no evidence of warp or cracks in the head.

I'm figuring it could be a couple of things - I had a Saab 9000 at one point where the previous owner had put some sort of coolant additive in. It didn't appear to cause any problems until i had the coolant flushed (when I lived in Canada, generally a good idea before winter). After the coolant flush wherever the gunk had been hiding it came out from and clogged something in the radiator and other things in the coolant system. I fixed that by flushing/driving/flushing 8 times to get it all out. Since I don't want to pay somebody to do that just b/c it's tedious I'll do that myself over the weekend.

If that isn't the problem, the only thing I can think of is the bypass valve to the thermostat. However I don't know how that valve works, how it's supposed to work, why it might not work ...

Anybody have any experience or knowledge of the bypass valve itself?

thanks
Andrew

1983 300SD