Water Temperature Sensor Curve Chart for 308 GT4

Don't have a chart; but, maybe this info will help:

A good friend w 308 thought it was overheating due to gage. Spent a lot of time & effort checking T-stat, coolant flush, W/P etc-etc. He replaced the sender, and still read hot. I clamped a little thermocouple to the housing where the temp reads, and he sarted it up. My thermocouple looked good. IIRC it was like 140 - 160F. It wasn't blowing out water and it didn't give any sign of being hot except what the gage was reading. He took it to his mechanic armed with all the info, he could gather, and the mechanic replaced the gage ------ problem solved.

It would be great to test the gage some how. Maybe, generate curve from a new sender?

 

Hi All

Reviving this very old thread (incidentally some great information here that I’ll maybe have to use).

Having what appears to be a gauge/sender issue that I can’t figure out. Will use the chart posted above to try to test both but thought I’d see if anyone had any experience with this.

On recent drives gauge temp shoots up to around the 3/4 mark. I pull over, shoot the radiator and block with an infrared thermometer, temperature seems well under what the gauge is showing. Also, the gauge seems jumpy with the engine running or off w key in accessory position.

Video of gauge issue here
https://streamable.com/9k8jz2

And temperature video here
https://streamable.com/d6l00t

Before I pull the gauge and try to get to the sender (I understand it’s not all that easy to access) I thought I would check to see if anyone has any ideas where to start. Looked around for past posts about this and someone suggested a blown head gasket could be to blame?

thanks in advance for any help

 

The water temperature sensor (#35) is mounted in the crossover pipe #27 between the cylinder heads:

https://www.ferrariparts.co.uk/diagram/ferrari/308-gt4-dino-1976/017-water-pump-and-pipings

Would be best to aim your infrared thermometer at pipe #27 to compare to the gauge in the dash (but something does seem wacky electrically with the needle bouncing around like that -- the thermal inertia of the coolant and metal pipe #27 makes quick changes like that virtually impossible to be real).

 

Thanks so much Steve. Will shoot that area tomorrow and see what I get.

Is it possible a bad ground from the gauge itself could create the bouncing? Or do the gauges periodically need to be recalibrated by a shop like Palo Alto Speedo?

 

I don't know. We have a lot of reported experience here that: 1) grounding the sensor wire = the needle goes to max, and 2) if the ground of the gauge floats up to a small positive voltage (from the way it shares the ground path with the instrument lights) = the needle moves up a little, but I can't recall anyone posting what happens if you disconnect the ground wire from the gauge (and I've never done that). Others -- please post what happens if you disconnect the ground wire from the gauge if you have experience doing this.

My short answer here is "no" for the gauges. AFAIK, the gauges don't have any (or few) active components inside so, unlike the tach and speedo, very few reports of a gauge going bad and needing to be replaced or repaired or recalibrated IIRC. Not saying that a gauge can never go bad, or need help, but it definitely isn't something that been reported/discussed a lot. The sensors with moving parts inside (like the oil pressure sensor) are more often reported as failing or being wacky.

 

I think it figured it out. Pulled this connector apart and cleaned some gunk out, cleaned up the spade connector and now the gauge seems to be functioning normally! Next up is getting both fans to go on instead of just the one…

thanks for the help Steve.
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I believe that the second fan is supposed to come on when the A/C is operating. Some (including my PO) rewired this so that it comes on along with the first fan to assist cooling the engine.

 

Gauge was still jittery so after reading a bit on this forum, realized the ground from the battery to the frame could be to blame. Cleaned it up and now that seems to have permanently solved the problem. Thanks for all the help.

 

Ugh spoke too soon. Gauge is right back up but temp on the thermostat housing is normal. Got a new sender but no matter what we tried, could not get the old one out. It’s an odd 21 so we didn’t have as many options to get on it. While we had the sender wire off, we replaced the spades because the wire looked fine. Then we tried grounding the wire and my gauge only went to 3/4 rather than all the way pegged at the top. Pete’s gauge went to 1/2 rather than all the way. Does anyone know for sure that grounding the sensor wire should send the needle to max?

 

*Gauge is right back up at 3/4 mark*

It doesn’t jitter as much as it was but still reading 20-30*C too high

 

No, they both come on when the temperature threshold is reached. One comes on when the a/c is powered.

 

I stand corrected, close inspection of the WM and electrical diagram indeed shows both fans are connected thank you!

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Checking back here. Has anyone been able to confirm that grounding the sender sends the needle to max?

 

http://www.panteraplace.com/page205.htm

useful and informative info on the Veglia gauge.

 

As a follow up here, finally resolved this issue. It was the gauge itself. Found a NOS gauge that I installed and now it’s working as it should. I’ll have the other repaired if anyone is looking for a gauge.