Just last week, engine started running at ~ 100C when heat is not on and at stop light. If stopped, turning heat on, temp comes down to ~ 85- 90. If cruising, temp stays ~ 85-90.
Any thoughts? Pryor to last week, engine ran consistantly at 85-90.
Thanks
Cliff

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1983 300d~250k Sold
1985 300d~185k
1999 Volvo V70 wagen 109k
2001 Dodge Ram 1500 78k

T-stat stuck closed? Low coolant level? Bad expansion tank cap? Bad fan clutch? Worn out water pump?

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Start with the most obvious and work your way back..................
1. Low on coolant. Add some!
2. Loose water pump belt slipping. If your alternator has problems keeping the battery fully charged in stop and go driving, this is a good clue since the water pump and alternator use the same belts. Belt will squeal upon acceleration.
3. Bad fan clutch. If it spins too freely with no resistance and motor off, this is your culprit.
4. Bad thermostat. Won't open completely making engine run hot.
5. Water pump failure. (Usually accompanied by leaks at base of water pump.)
6. Lower radiator hose soft and spongy causing it to collapse upon acceleration and making engine run hot at subsequent idle. You will need to rev up yopur motor to 3000 RPM with the tranny in park with hood open and watch to see if lower hose is sucking in on itself.
7. Engine block so full of coolant crud engine cannot cool down properly. This usually happens over a period of time though and not a sudden change.
8. Low on oil and/or oil cooler fins clogged up with debri along with radiator.

The above possible causes and solutions assume your temp sensor is working properly.