[tchudy]

Completely rebuilt the engine in my 86 944T recently. I installed a secondary water temp sender/gauge for better accuracy. The sender is installed in the metal hose section of the upper radiator hose near the bleeder valve. The temp of the secondary gauge has been mostly in line with the dash gauge until recently (dash gauge sending unit new also).

Up until last week I had only driven the car around locally, not going much past 50 mph. I put around 50 miles on the car during this time and no temp issues. Had to drive slow due to the old tires on the car. Now have all new rubber so I have been driving a 20 mile circuit on the highway at up to 70 mph, keeping the RPM's below 5k. The first three drives went fine...coolant temp no higher than 90c on both gauges.

Took a ride early today and I am seeing the temps on the secondary gauge reach 100c. The dash gauge looks to be in the 90c range...maybe just a bit over (according to Clarks Garage info). I spent the day bleeding air from the system several times to make sure I had it all out. I do have a Lindsey Steam Vent and I do not have more than a few small air bubbles visible in the tube. I rented a pump to pressurize the system to check for leaks and push out the air just to be 100% sure. I also replaced the temp sending unit for the secondary gauge, just to make sure it wasn't bad.

No luck. Next drive...locally, not on the highway. Temp on the dash gauge reading 90c and secondary gauge reading 100c. I am not sure why the big difference. I tend to believe that the reading on the secondary gauge is good but I don't know why they would be different. After my drive I sat in the car at idle and the temp of the secondary gauge was increasing beyond 100c...so I shut the car down.

Next step...check the belt tension. Is it possible that the belt has expanded a bit since install and the pump isn't turning well? How about the thermostat...should I pull it & test? By the way...water pump and thermostat are new.

I don't trust the dash gauge because it isn't specific enough...so I am left with trusting the secondary gauge.

Any ideas would be appreciated.