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Old 06-12-2002, 11:24 AM
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pmizell pmizell is offline
Benz Zealot
Join Date: Jun 2001
Location: Houston, Texas
Posts: 838
Exclamation My 300E running too cool!

Hello gentlemen,

This one has me baffled. My M103 engine is running waaay too cool (or at least appears to be) at around 76/77 deg C fully warmed up. Sometimes it will run at this temperature with the ambient at 81F or 93F -- no difference, sometimes not, but if engine temp does rise, it'll barely touch 80c. Gas mileage is way down due to this condition.

Occasionally I'll catch the needle "dancing" just a little.

Things I've checked:

1. thermostat - changed it out, no difference.

2. coolant temperature sensor - my '91 M103 (103.983) has this sensor on the head itself (two pole blue). This was recently changed due to an aux fan problem, so I doubt this is the cause. I've double checked the connections -- no problem there.

What should I check next? Does the coolant temperature sensor serve as the engine temp sensor? Are these two different sensors?

The "dancing" needle leads me to believe that whatever sensor/relay/etc that controls it is bad.

Please offer any insight you may have.



'91 300E, 212K miles
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