Water Temp Gauge

reservoirdog · Post by **reservoirdog** » Sun Aug 19, 2007 11:02 pm

I'm getting false readings on my water temp gauge - I've had my mechanic test the radiator hoses and they are below 200, but the gauge pins anyway. Some have advised pulling the connection to the sensor on the top of the motor, others recommend I just get a new gauge, which I have ordered from Summit Racing.

Anyone else experience this?

So Cal Mark · Post by **So Cal Mark** » Sun Aug 19, 2007 11:04 pm

if the thermostat doesn't open, the water in the block will be much hotter than the hoses. But, I have seen many faulty sending units. Are you installing a mechanical gauge from Summit?

reservoirdog · Post by **reservoirdog** » Sun Aug 19, 2007 11:10 pm

No, I was going to get an electrical one. I thought mechanical would be hard to install. The sending unit is new, and the fan seems to come on. Wouldn't that imply the thermostat is opening?

So Cal Mark · Post by **So Cal Mark** » Sun Aug 19, 2007 11:57 pm

the fan won't cycle properly if the t-stat isn't opening. Will the replacement gauge come with sending unit and adapter to fit the head?
Does your current gauge stay pegged all of the time? or just after it hits 200?

reservoirdog · Post by **reservoirdog** » Mon Aug 20, 2007 12:14 am

I assumed I could still use the Fiat sending units, both of which are new (head and radiator) - do you think that is a problem? I have a mechanic wiring for me. The engine is substantially rebuilt.

Gauge rises fairly quickly thru the temp range, sometimes it takes awhile until it pins. Even when pinned, the car has full power and the hoses seem normal size.

I'm using a local (NY) shop that always has 2 or 3 Fiats there, so I'm fairly comfortable with them. They feel the gauge could just be bad after all these years.

Really appreciate any insight.

So Cal Mark · Post by **So Cal Mark** » Mon Aug 20, 2007 12:57 am

I doubt the oem sending units will have the right resistance for an aftermarket gauge; I haven't ever seen that happen. It sounds like the temp sender for the top half of the gauge is bad. The fan should turn on at 195 and drop the temp to under 190 before it cycles off

Hawke187 · Post by **Hawke187** » Mon Aug 20, 2007 9:33 pm

If the problem is that the gauge reads high, but the actuall temp is normal, then yes I have had the same problem.
What it ended up being was the forward sensor ( the over heat switch ) was acting like a variable resistor (just like the temp sense) with both connected the reading was a false high.

The easy fix is just to disconnect the forward sending unit and insulate the wire.
If you are a guage watcher then the over heat temp shitch sensor is not needed anyway.

This fix is thanks the Apsen Motors in Denver, he is one hell of a Fiat Guru, not to mention he saved me a bundle on troubleshooting this further...

Let me know if this is the problem.

Hawke