Mine jumps a little too. I put it down to a heat sink when the car's idling with slower coolant circulation.

I don't know if others do the same but after the car has been stopped at normal temperature and started again after a short time the temperature can be up enough to fire the electric fans ie about 107 degrees. Usually after a high speed run.

I think it's related.

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1990 300TE

"24 hours in the day. 24 beers in a case. Coincidence? I don't think so."

Got my car back today from the shop. Driving on the freeway it stays about halfway between 80 and 100. Sitting at a stop for a while, it climbs to about 3 mm above the 100 degree mark and stays there (in 75 degree weather today). Definitely running hotter on the gauge than my last engine. Not sure why. Same radiator, different water pump and different water temp sensor??? Is this a good thing?

Check out K6JRF dot com the cool harness he sells brings the electric fan on at a lower temp. Has worked well on my 88TE. Purple Ice also helps. Running a lower percentage of coolant works depending on climate.

sptt, what brand and rating is the thermostat? Is the water pump aftermarket or genuine MB?

The shop that did the engine swap should have ensured that the engine/cooling system was performing properly before considering the job complete and allowing you to drive off. You need to find a reputable shop that knows MB automobiles and how to work on them. No responsible shop would return your car to you with those issues, knowing the recent history.

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Fred Hoelzle

Ferdman...I don't know the brand I have now but am going to go buy a Behr T-Stat (79c rated) tomorrow. I think this is an MB waterpump from what I can tell. One thing I did notice is that I don't have all of the pressure in the upper radiator hose that I had before with the old engine. I can feel the water flowing through it and it is hot like my other one was. The auxillary fans are coming on at the right temp with A/C on and at right speeds. Unless you went and drove it for a long time and then stopped and idled for a while, you wouldn't get the needle rising (I tried to just sit there today for a long while and it just stayed above the 80c mark). Could I have a water temp sensor issue misreading the actual temp? After the T-stat opens, does it just stay open while hot or does it vary? I'll try the new T-stat first as it did improve a little when I replaced the one in there with my old. Could the fan, with a new clutch not being as close to the radiator, make a difference (it's about half an inch loser to the engine now).

Sounds like a tired water pump....tell your mechanic to change it free of charge since he didn't test it and should have if he has thrown your engine away already.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
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2003 Gray Mercedes ML350 - 122k

ps2cho...It's an MB waterpump and looks good. Should there be some noticeable pressure in that top hose? Is there a way to check? I replaced the T-Stat today with a new Mercedes Benz one. Did nothing. Napa and MB Deler also told me you could not get a 79c T-Stat for these cars. Frustrating

Looks does not mean it is good. Like I said before, higher the pressure in that top hose, the higher the suction. The propeller inside could be worn out.

The service guy you went to is a moron. Part #100-200-07-15

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

I think you are correct. The coolant is probably not circulating fast enough. When I turn on the heater, temp drops immediately. I should have been a mechanic. I have the other waterpump still so I'll change it out as soon as I get a chance. That really ercks me!

Thanks

sptt, the engine in your 1988 300TE is designed for an 87 degree C thermostat. Presuming all the cooling system components are functioning properly the 87 degree C thermostat will allow maximum engine efficiency.

I agree with ps2cho. The appearance of the water pump is irrelevant. The condition of the internal components is critical. If the impeller is shot then the water pump is not providing adequate coolant flow through the cooling system to maintain the 87 degree C operating temperature.

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Fred Hoelzle

It is not so hard to check the function of a water pump and thermostat.

If there is a large difference in temperature between the radiator inlet en output and the car is running hot, the circulation is bad.
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If the coolant circulation good:

If there is little difference in temperature either the radiator is not good or you have a restricted airflow.

High temperatures at low speed and normal at high speed mean that the fan clutch is not working.

High temperatures at high speed indicate a bad radiator of blocked airflow.

Rob

Finally replaced that original MB Waterpump today with a new one. Old one did look very good inside and I could not see any signs of corrosion or impellor degradation. No play in pulley either. Installed new one and started car. Same amount of pressure and coolant flow felt on top hose as with other pump. I was able to easily blow through the radiator top and bottom with no restriction while everything was off and drained. Could it be in the engine...??? Fan clutch works fine. It has been consistently in the 100's out here but when it drops to 85 degrees outside or lower, temp gauge reads between 80 and 100. Otherwise, it's right below 100 and climbs to 105+ when sitting at lights.

check your cooling fans...they might be ...the electrical connection might be connected backwards...it happened to me on my 91 300TE and it now runs perfect.

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I have never met a man so ignorant that I couldn't learn something from him. -Galileo Galilei, physicist and astronomer (1564-1642)

I had already checked the cooling fan direction from your previous post in this thread. They are fine and run in the correct direction.

sptt have you verified the fan clutch is working (roaring)? The clutch fully engages at 90C and is critical to engine temperature between the 90-100C mark.

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1991 300E - 212K and rising fast...