MY 90 305 TBI temperature gage doesn't work all the time.. But when it does it doesn't always show the temp at 210-220, sometimes it will climb as high as 240-250 while sitting in a drive through or something..

I'm starting to worry I am overheating it so I want to get the temp gage fixed. Where do I start? (Besides at the mechanic, that is)

 

The easiest thing to access is the temp sender itself. The one that runs the gague (not the CTS for the ECM) is in the driver's side head between the front two spark plugs. It's not a weatherpack connector, so the possibility of corrosion or a poor connection there is higher. It's just a single wire and works on a resistance-to-ground type setup. That wire fully grounded is full-hot on the gague, very high resistance is full-cold on the gague. Also, the sender itself sometimes goes bad.

That's where I'd check first before tracing wires through the harness or blaming the gague/gague cluster in the dash. They don't always read perfectly accurately in these cars, but generally they read reliably.

 

Thank you very much for the reply! So check that wire/connection and go from there?

 

I have further identified the temperature gage is working now that I have cleaned a few components and doublecheck connections, but I also identified a separate issue which is causing the attempts to rise above the 210 to 220 they should be.. The fan is only kickin on if I turn on the AC!!

 

i think the factory fan kicks on around 230

 

Sounds about right... So if it doesn't?

 

replace the fan switch

 

Eureka! I'll try that next...

 

Fan switch (temperature-referenced) is the sender in the pass. side head between the rear two spark plugs.

The aftermarket has an array of fan stich senders in different temperature ratings. The stock switch kicks 'em on at 228*, if memory serves (and A/C is not activated). That's AWFUL high. Something in the 200-210* range would probably be preferable in a performance-oriented application.

I rigged up my own system that retained the stock fan switch sender but ALSO had an in-line fuse holder to run the fan constantly if I installed a litttle 1A fuse. For use primarily at the track or in hot weather.

You could just as easily use a manual switch inside the car to activate it as-needed.

The fan switch is just a "continuity to ground" type setup. You can patch a switch or whatever you want into it to give you full-manual override control to turn on the fan whenever you like.

Also, there is a tech article on this site that has some great info about how the stock fan systems operate and how to modify them for better performance and temp control.

 

Thank you for that very thorough reply! I had a few days off and took the chance to leave town for a few, but now I am back at it and ready to tackle this issue.. Stay tuned!