Cooling System problem?

[ga.spyder]

I am having a issue ,so I thought I would throw it out for some expert opinion.At FFO ,I was invited on a ride w/ the 'Jersey Boys' and I noticed my car was running a little warm. Not hot ,but above the 0 in 190.It never runs above the 9 in 190.The next day I was sitting still in line for the show area and my temp climbed to above 210.The fan hadnt come on either. I was debating if I should go on the long ride after the show ,but I took off anyway.The temp rose to 200 and I was going to turn around when I hit a bump and the guage jumped(not slowly crept ) to 190 and stayed for the whole ,hard ride.I got home and bled the system well and ran it around ,it stayed under 200.I sat still in the driveway ,and it started climbing to 230!All the sudden it snapped back to 195 and stayed thru 2 fan cycles.Wiring to the guage? Bad guage? I jiggled the sending unit wires and it didnt change anything. When the guage climbs and reads hot ,the car doesnt seem to be hot.Any suggestions where to look for this little gremlin is ,as always ,appreciated.
Craig

[kristoj]

Craig,

My guess is that it is the sender, not the gauge itself. Not sure how much the sender runs, but I would start there.

[ga.spyder]

Hey John ,the sender is fairly new but that doesnt mean it cant go.I may still have the old one which was working.It is an odd deal ,I have never seen a temp gage jump like that. It jumps back and forth like an amp guage. If I remember the sender closest to the 't' is an overheat sensor ,the actual guage sender is between #2 and #3 cyl ?I hate to take a chance overheating.
Craig

[kristoj]

Yeah, nothing more disturbing than watching your temp gauge rocketing toward the red zone--except maybe that time my BMW low oil pressure light came on at 75 MPH on the freeway. That turned out to be a bad sender. I can't remember which sender is which on the top of the head, but I'm sure someone here knows. I have an extra temp gauge I bought on e-bay a while ago that I could send you, but it is off a turbo and they are different. Mine has "NO BOOST UNTIL WARM" printed across the bottom of the gauge.

Steven Rankins is parting out an '81 Spider and may be able to supply a gauge for you -- check in the parts for sale section. I just bought a couple bits from him myself.

[So Cal Mark]

the red sender is the temp gauge, the black sender is the overheat. Try disconnecting the black sender, I've run across several bad ones lately that have resulted in erratic gauge operation

[manoa matt]

A laser thermometer is a sure way to tell the actual temperature of the head near the sensor. Also good for checking the inlet and outlet temperatures of the radiator,the thermostat, and the temperature near the fan switch.

[Jim DeShon]

I'm with Matt here. I would want to verify that the cooling system is OK and not just assume it was the gauge or sender. If you don't have a laser thermometer you can use any themometer with a high enough range. I duct tape it to the top radiator hose and run it in the shop until the fan cycles a couple of times. Verify that what the gauge reads is correct. Then you know for sure if you have a gauge or cooling system problem. ...J.D.

[ga.spyder]

Thanks ,guys. I crew for a top alchohol dragster ,and we have a laser thermometer in the crew box. I am going to borrow it tomorrow,after chasing my grounds ,wiring,and swapping sensors.I'm with you on not taking a chance on overheating.I really think it is in the wiring/guage but better safe than rebuild!
Craig

[kristoj]

If your gauge is jumping suddenly as you described, it has to be an electrical issue. However, as others have pointed out, it would not hurt to get an accurate temperature reading in the unlikely event you have an electrical issue AND an overheating problem at the same time.

Let us know how you make out.

[ga.spyder]

Thanks everyone ,the demon has been exorsised.It was either the overheat sensor(which I disconnected) or the wire from the temp sensor(I put a new end on it).I was headed to the race shop for the laser thermometer ,never got above 185 deg.Fan came on at 200 thru 3 cycles.Suprisingly ,my guage is pretty accurate going by the laser readings.Put 70 miles on her ,thru the mountains....perfect.
thanks again ,Craig