Does anyone know what the wire from the thermostat housing that looks like it goes to the turbo is for?

thanks
Andrew

1983 300SD

 

Flushed the cooling system, rinsed, flushed again, took 3x before everything ran clean. Now the car is running about 85C after full warmup, low speed driving (around 40mph) but plenty of stops and starts.

Except for the odd spike to 95-100C, after which it cools back to around 85C.

Was watching the engine and happened to notice every little while the water pump stops turning with a short grinding sound. Watched the temp gauge and listened for the sound, sure enough, that's when the spikes happen.

Bearings on the water pump must be almost gone.

Cleaning it out did bring it down to normal operating range except when the pump sticks, so definitely worth my time doing it. Those spikes put it to boil over point when it was running hotter overall.

Andrew

1983 300SD

 

Thanks for the responses and assistance.

 

So I'm assuming if that hose is disconnected that the heater should just work. Would there be any other effects if it is disconnected?

thanks
Andrew

1983 300SD

 

With the thermostat in, is there anything that, on the assumption the thermostat itself works, would prevent coolant from circulating to the radiator through the bottom hose?

Currently the engine is not actually overheating, and the sudden large temp spikes from the water pump stopping have gone, but it does run hot (around 100C), the gauge still has the odd sudden jump to about 105C then almost immediately back to 100C, and the bottom hose remains at most lukewarm, even after a fairly long trip, as though the only heat getting to it was from coolant from the top hose slowly mixing through the radiator. There is plenty of heat if the heat is turned on, but turning it to A/C has no effect on engine temperature, as one would expect if the radiator was the problem. Flushing the radiator manually there is very good flow in any case.

With the bypass valve design I don't know how to test the flow through the block to the thermostat, to test whether the thermostat is seated properly, opens at all, etc. or whether water actually gets to the thermostat at all. If I were to guess, I would guess it doesn't right now. THe outside temperature only affects how long it takes for the engine to warm up, but not the operating temperature (we had a cold front come through and at 19F out it behaved the same as at 75F).

Update: This morning is freezing cold out, after the engine running at a consistent 100C for 15 minutes and then idling for 5 (during which it dropped just under 100C) the radiator feels ice cold. The upper hose is hot, the lower hose is cold.

I'm guessing also that it is running rich, due to the grey-black smoke after idling at a light when hot. It also starts perfectly cold (at 19F, completely cold engine, the starter had to turn over only once) but is more difficult to start hot. I tried to replace the air filter but couldn't get the filter housing open, it appears as if it is fused shut - don't know whether that was intentional but I can't think of any good reason to do it, on the other hand I can't think of any reason it would just happen.

thanks
Andrew

1983 300SD

 

Ok, it is disconnected (looks to be intentional), and the heater works, although the blower doesn't. If the car is over 40mph the interior gets very warm with the heat on, and gets very cold with the A/C on.

thanks
Andrew

 

I figured out at least part of why I was being stupid - the coolant travels the opposite way from most cars. Which means the high pressure in the top hose is most likely just due to lack of proper flow through the rad, not from the thermostat not opening.

I got an infrared thermometer and it shows the flow is sufficient after the flushing and new water pump to keep the car at about 98C, except when it first warms up - the pressure has to get high enough to force water through the rad, and that doesn't happen until about 110C, which is when it suddenly drops back to 80C, then warms back up to 110C, back down to 80C, and then warms up to 98C and stays there. Coming off a short highway run it does go up to about 106C and stays there unless i stop the car and put it in park for a few minutes to let it cool back down (or turn it off, in which case it cools back down much quicker).

The infrared thermometer shows only a 3-4C delta between the thermostat and the hottest parts of the engine, so it looks like it's doing enough, at least while it's cool out, to not cause any further damage. Wouldn't want to take it far or drive on a hot day though.

Pointing it at the rad shows the problem, large areas of the rad show only the warming you would expect from being close to other warm metal, not the heat from water inside. It looks like the rad, like the water pump, are the original ones on the car and really 31 years is probably a bit much even for a Benz rad.

There's a fellow local who runs his own Mercedes shop and has about 35 years experience as a Mercedes specialist. The prices are reasonable (unfortunately it's about a 25 minute drive, so it's a pain if the car isn't actually running) and he guarantees everything for 2 years parts and labor. He's quoted me around $350 for a new Behr rad including labor, but he wants to wait until the outside temp gets back into the 70's so he can properly test it once it's in.

So for the next week or so I'll just drive it short distances and avoid highways.

Now to try to figure out how the vacuum system works.

thanks!
Andrew

1983 300SD