Bad coolant sensor or worse?

Post by **mgjh** » 29 May 2010, 16:07

1988 240 wagon. Have to keep reminding myself this is a $400 (fun) project...was idling engine for about 45 minutes in the driveway when I happened to notice that the temp gauge was just below the red. Engine is running fine, no smoke or anything. Coolant is circulating (hot radiator & upper radiator hose, pump seems fine). Also, on a cool morning a few days ago I went out, started it up, and the temp gauge shot up again (cold engine). Car also has trouble starting in hot weather, but starts right up when temp is below 50 degrees. Finally, there seems to be more than the usual amount of water out the tailpipe, but car's got old gas from sitting for months over the winter before I bought it. I've read this could be the coolant sensor for both temp gauge & start problems. Anybody have any other ideas? Could it be something more serious? If it is the coolant sensor, should it be replaced immediately or can it wait a few hundred miles? Thanks.

claymore850 · Post by **claymore850** » 29 May 2010, 18:40

Start cleaning the sensor connector, sometimes it has some rust, and send wrong info to the ecu.. If the problems stills replace the sensor..

Did you check your oil??? no water??? Are your radiator loosing water??

Post by **mgjh** » 14 Aug 2010, 07:12

Actually had a buddy check engine temp with an infra red thermometer & all is fine, so I'm not going to worry about it right now. I might try swapping out the instrument cluster at some point since clock and odometer are also out.

Maroonbrick · Post by **Maroonbrick** » 08 Mar 2011, 17:41

I wonder if your problem was solved? I just had a coolant temp sensor replaced in my 94 850 Wagon. The car was very hard to start, and the fan was running constantly. The mechanic told me that the temp sensor was bad and that this would cause the hard starting as well as the fan issue. I just got the car home and I'm waiting for tomorrow morning to see if the car starts. I'm not sure what the connection could be between the temp sensor and the hard starting, but from your post, it does sound like there is a connection. Any thoughts would be greatly appreciated.

Post by **jimmy57** » 08 Mar 2011, 19:09

The 240's have different sensors for gauge and fuel system.
85 and later 240's have notorious problems with the temp gauge. There is a circuit board on the instrument cluster main backboard that is there to STABILIZE the temp gauge. When it has connection troubles it CAUSES instability.
Many have been replaced but the usual real problem is either 1. temp compensation circuit solder flux in sockets that grasp the pins sticking off the main board. Clean the sockets with a straightened paper clip and then push the sides inward for a tighter grip and then scrape the pins sticking up off the main board. Apply a little grease to pins and re-assemble. OR 2. the grounds between engine and chassis and chassis to cluster are not good and alternator charging load is messing with the signal as that fools around with poor grounds and resultant voltage drops. Or both issues.