75C thermostat - PeachParts Mercedes-Benz Forum

Paulc66t · #1 07-19-2007, 08:18 AM

Does any one know where to get a 75C thermostat for a 617 motor?

Thanks,
Paul

lkchris · #2 07-19-2007, 08:42 AM

Cooler thermostat not a good idea.

Brian Carlton · #3 07-19-2007, 08:47 AM

What would be the reasoning behind a cooler thermostat?

If the cooling system (radiator, water pump) is functioning properly, it won't allow the engine to get above approx. 95C...........the maximum opening in the thermostat.

If a cooler thermostat is utilized, the engine will still reach 95C. if the remaining components are marginal and the thermostat is fully open. You'll have some additional margin in terms of time required to reach 95C., but, this benefit is offset by the undesirable characteristic of running the engine much colder than desired for 99% of its operating time.

dieseldan44 · #4 07-19-2007, 09:18 AM

Hey Paul,

What temps are you running at on the highway these days?

Have you happened to check your head temp with an IR gun to verify the gauge?

dd

Gurkha · #5 07-19-2007, 09:37 AM

MB uses 72C thermostat in India for their OM616 turbo as well as for the OM617 turbo to compensate for the gruelling summer in north, keeps the engine temp at a happy 80c-82c max zone. Its probably to compensate for the smaller radiator size in these engines when they were originally made. My Gurkha with OM616 turbo has 72C thermostat.

LUVMBDiesels · #6 07-19-2007, 09:46 AM

I got one by ordering part 116-200-00-15 (G4001-15459) at autopartsdwarehouse.com. I have not installed it yet so I do not know if it will make any difference in the temp of the car.

Gurkha · #7 07-19-2007, 09:51 AM

Under extremely hot conditions driving full load uphill, you will see a difference with the lower rated T stat.

Brian Carlton · #8 07-19-2007, 10:10 AM

Quote:

Originally Posted by Gurkha

Under extremely hot conditions driving full load uphill, you will see a difference with the lower rated T stat.

The only difference that you will see is time.

After sufficient time, the two systems will stabilize at the same engine temperature.

Naturally, M/B would hope that the hill would have ended by that point...........

It doesn't seem like a good compromise unless the expected full load events in very hot weather are often and extended.

Gurkha · #9 07-19-2007, 10:17 AM

Well, its MB who came to this solution of 72C thermostat, going by the average long and hot summers in north here. Works out well, I have driven in 52C heat as well as -15C and the temp stays between 80C-85C max.

#10 07-19-2007, 10:41 AM

Quote:

Originally Posted by Brian Carlton

The only difference that you will see is time.

After sufficient time, the two systems will stabilize at the same engine temperature.

Exactly, in the U.S. most drivers will never see 50C ambient temperatures, it's not worth having the engine operate at 75C all winter to keep it from hitting 100C on a rare hot day.

I just drove my 300D (with a 80C thermostat) about 1100 miles in 35-40C ambient temperatures and it stayed between 85 and 95C with the exception of some very long/steep hills (5-6% grades) when it touched 100C. That's driving at 75-80 mph with the AC on. BTW, this car has a new radiator, it ran about 5C higher with the old one.

The point is, you should not need a 75C thermostat in the U.S. if your cooling system is operating correctly.

Gurkha · #11 07-19-2007, 10:46 AM

My temp never hit 75C, even at -15C weather.

Brian Carlton · #12 07-19-2007, 10:46 AM

Quote:

Originally Posted by Gurkha

Well, its MB who came to this solution of 72C thermostat, going by the average long and hot summers in north here. Works out well, I have driven in 52C heat as well as -15C and the temp stays between 80C-85C max.

If the cooling system can keep the engine at 85C with a 70C stat, presumably, it can keep the engine at 95C. with an 80C stat.

I fail to grasp the benefit of the lower stat, unless India needs a cooler running engine than the remainder of the world.

vstech · #13 07-19-2007, 11:00 AM

So Brian, are you saying the 617 diesels are supposed to stay around 100C under normal conditions? I thought they should stay around 80C... no? I have been fighting this car since summer started to get it to stay at 80 and everything I do makes it hover at 100. it warms up directly to 100 and stays there. verified with IR NC thermometer. I have not pulled the waterpump yet, but it is next on my list. cooling system is SPOTLESS double acid flushed. strong acid washed the condenser and the radiator. the thing is cooling the lower hose down around 110°F so I know the radiator is perfect. the coolant is staying clear, so no corrosion in the block. and the new 80C thermostat is in. I was going to drop in a 75, but you are saying no. I plan to change the water pump and pulley and fan to get a bit more spin and flow. but if you are saying 100C is great, I will leave it alone.

Gurkha · #14 07-19-2007, 11:04 AM

Quote:

Originally Posted by Brian Carlton

If the cooling system can keep the engine at 85C with a 70C stat, presumably, it can keep the engine at 95C. with an 80C stat.

I fail to grasp the benefit of the lower stat, unless India needs a cooler running engine than the remainder of the world.

95C is too hot for conditions here, the oil thins out, under load it would easily touch 100c, at 80c, everything runs fine, oil stays in proper condition, 80c is what almost all engines run generally, most Japanese engines do.

Brian Carlton · #15 07-19-2007, 11:18 AM

Quote:

Originally Posted by vstech

So Brian, are you saying the 617 diesels are supposed to stay around 100C under normal conditions? I thought they should stay around 80C... no? I have been fighting this car since summer started to get it to stay at 80 and everything I do makes it hover at 100. it warms up directly to 100 and stays there. verified with IR NC thermometer.

The 80C. thermostat is closed all the way to 80C. It starts to open at 80C. and is fully open by 94C.

So, a cooling system that has the capability to keep the engine stable will not allow the temperature of the coolant to go above 94C.

If yours stabilizes at 100C. and won't climb above 100C. then the difference between 94C. and 100C. can only be attributed to slight differences in water temperature between the point of measurement and the thermostat..........or the gauge............or the thermostat itself. In any case, it's not worth further discussion for a difference of 6C.

The key is the fact that the engine is stable at 100C. The cooling system is keeping up with the heat demand. If not, and it climbs to 105C., then you've got some additional investigation to do.

If you had a brand new system, the temperature would stabilize at a lower temperature for a given mode of operation. This leaves additional margin on the top end for any extended heavy load operation.

Your only issue with 100C. temps is the fact that you cannot climb a hill under full load for more than 60 seconds (estimated). The demands on the cooling system would be greater than the capability of heat dissipation and the engine would climb well over 105C. But, that's the purpose of the gauge.

FWIW, the SD will climb to 95C. and sit there with the a/c running. If I climb a hill under full power, the temp climbs to 100C. I presume that it would continue to climb, but, as usual, I ran out of hill after about a mile or so. But, I'm quite sure that I could not take it on a five mile upgrade at full power without the temp. climbing to unacceptable levels.

The SD will benefit significantly by cleaning the radiator fins. This is the typical culprit for higher than desired temperatures (5C. or so).