Temp gauge

Mark_vaughn · Post by **Mark_vaughn** » Thu Sep 21, 2006 9:30 am

Well, I didn't miss it before I knew it existed. So I guess I don't need it.

mbouse · Post by **mbouse** » Thu Sep 21, 2006 9:38 am

if you are not having coolant temp issues, i would not recommend finding and replacing it.

if you can't seem to figure out overheating, i would suggest putting a pan back in place.

most belly pans can't be seen unless you are looking for them, and unless you have remote a oil filter kit, they do get in the way come filter change time.

perthling · Post by **perthling** » Thu Sep 21, 2006 8:16 pm

I thought I had an overheating problem when I was driving to work - the temp gauge was almost at the half-way mark and I was starting to get a bit anxious. Then when I was driving home the temp gauge was back to normal (about 1/3). The difference? When I turned on the headlights, the gauge jumped up about 1/5 of the way. Not sure what the cause is, but obviously there's some sort of gremlin in my electrics (what? in a Fiat?

) which affects the temperature gauge.

spider2081 · Post by **spider2081** » Thu Sep 21, 2006 9:09 pm

I believe the temperature guage meter movements ground and the guages internal panel light share the same ground. If the guage displays a different temperature when the lights are on I would remake that ground and see what happens

Torxx · Post by **Torxx** » Fri Sep 22, 2006 10:34 am

I brought the car up to operating temp and checked the hoses and the bottom of the radiator and all were hot.

the heat does work.

the fan does work, but does not come on every time the temp gauge reads higher than 195 deg.

i have not found the time to bleed the system for potential air pocket yet.

does that give any clues?

when i read these posts i am envisioning a old chevy engine compartment to work in, when i actually open the fiat hood it looks tight to work on and i anticipate bleeding knuckles

So Cal Mark · Post by **So Cal Mark** » Fri Sep 22, 2006 10:59 am

if you have air in the system, the thermostat won't open and the bottom of the rad won't be hot. Have you looked at the water flow with the rad cap off once the engine warms up? Once the t-stat opens, water should be flowing pretty noticeably across the top of the rad core. Try feeling across the rad for spots that are cooler; that indicates a plugged rad.

Hawke187 · Post by **Hawke187** » Fri Sep 22, 2006 11:52 am

I had the exact same problem, the gauge was reading high, but with an infrared thermometer the head temp was reading 190-200 range while the gauge was just shy of the red line.
The fan came on and turned off as it should.
The problem turned out to be the overheat switch sensor, the forward of the 2 temp sensors on the top of the head.
It was acting like the temp sensor, not like a switch, with both sensors hooked up it was getting 2 resistance readings, causing an improper high temp reading on the gauge.
I disconnected the overheat switch and instantly the gauge dropped to the correct temp on the gauge as verified by the infrared thermo.
As I am a gauge watcher anyways, I just left the overheat switch disconnected and terminated the conector on the end.

I have had zero problems since...

It takes 2 secs to check this so it is worth a shot...

Let us know if this fixed it or not..

Hawke

Torxx · Post by **Torxx** » Fri Sep 22, 2006 3:02 pm

I will check water flow and the switch sensor (if i can id it).
thanks

update today. i took the car out for errands (city and highway mid 70 air temp) the temp gauge was up and down, always above the 190 mark and never into the warning area. the fan never came on. not even when i turned the car off, which usually kicks the fan on.. weird.

Torxx · Post by **Torxx** » Sat Sep 23, 2006 1:57 pm

now it looks like the temp gauge only comes on when the gauge reads into the warning area. No real sign of overheating though.

How can i test the actual water temp to verify that the gauge is reading prop... can i stick a thermometer in the radiator?

So Cal Mark · Post by **So Cal Mark** » Sat Sep 23, 2006 3:25 pm

thermometer in the radiator works just fine

Hawke187 · Post by **Hawke187** » Mon Sep 25, 2006 2:08 am

The best tool i found to help check the temp was an infrared no contact thermometer, they used to be quite pricy but Harbor Freight now has one for less than $20 , 26 if you get the one with the laser...
After the engine is warmed up all you have to do is point it at the top of the head and presto... an accurate reading.

As to the temp sensor and over heat switch locations, they are both on the top of the head in the valley between the cams,both have only one wire attached, the temp sending unit to the gauge "should" be the one closest to the fire wall and the overheat temp switch is the one right behind the water intake housing.
You can test them both very easy, just take the connectors off, try taking the front overheat one off first and then check the gauge when it warmed up.
If this is the problem, like it was on mine, the gauge should drop right to around the 190 point, almost dead center on the gauge.

You can short the Overheat wire directly to the block/ground and the temp gauge needle should instantly peg all the way over to the right.

The same will happen if you grounf the Temp sending unit as well.
I made the mistake of testing each one but left the other still installed.

You can sometimes verify the Overheat sensor is bad bydisconnecting the temp sending unit but leave the Overheat connected. If it is working properly the gauge should read 0, or dead cold. If it reads off the left peg at all it is probably bad.

If you are a gauge watcher the Overheat Switch can be left disconnected all together, just be sure to terminate or insulate the connector to keep it from shorting to ground.

I hope this helps, it only took me over a month or so to figure it out, and that was with the help of a local Fiat guru who took one look and had it fixed in less that 5 sec....

Real embarasing for a 25+ year aviation electronics tech...

Oh well live , learn and spread the word...

Hawke

Torxx · Post by **Torxx** » Fri Oct 27, 2006 10:52 pm

temp gauge update:

looks like the sensor Hawke187 and others mentioned is likely the problem, i.e., sensor on top of the engine on the front side... Iâ€™ll know for sure in a few days.

Torxx · Post by **Torxx** » Sat Oct 28, 2006 5:08 pm

sensor did not do it... bummer.

radiator checked out, fans work o.k., i guess i need to check the gauge itself

Mark_vaughn · Post by **Mark_vaughn** » Sat Oct 28, 2006 6:14 pm

I don't know if this is possible, but could the wires from the two sensors be mixed up? That would make both the light and guage not work properly.

Just trying to think like a Fiat.

So Cal Mark · Post by **So Cal Mark** » Sat Oct 28, 2006 8:03 pm

they could be switched.
BTW, do you still need throttle info on the 38mm carb? I took a couple of pix of my customers' installation. I can email them if you like

Temp gauge

temp guage