My son's new (to him) 86 SDL won't heat above 60* at its warmest. Usually around only 50*. When we got the car it acted like this so I changed the coolant and thermostat thinking the 'stat was stuck open. Didn't change. Next I was thinking gauge/sending unit because son tells me the heater works ok. Yesterday he tells me its taking a long time to heat compared to his 123. Says he doesn't get any heat till at least two miles (which I didn't think was so bad). So now I have a sending unit that may not be needed, since it appears the gauge may be accurate after all. What else could cause it to run too cool? I don't want it too hot, it is a 603 with a #14 head. We bought the car back in the fall before it got cold so this isn't a cold weather only thing. I know the car has a pump that maintains coolant circulation at idle (or is that the 617?), could this be stuck "on" and over cooling? Is there a bypass somewhere that is stuck? I obviously am at a loss here, any suggestions would be appreciated as I don't think it's good for the car to run this cool.

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Muleears
'07 E320 Bluetec 133K my DD
'04 Jaguar XJ8 VDP, 34K
'10 Hyundai Accent 60K Grocery Getter
'02 VW Golf soon to be on the road again
'97 E300 Diesel Son's DD
'61 VERY tolerant wife

Hampton Roads, VA USA

Gone but not forgotten:
'67 250S 95K
'86 300SDL
'87 300D Turbo, 364K! R.I.P.
'98 E300 Turbodiesel, 213K
'02 S420, 164K
'01 Prius 138K