False High water temp reading

Hawke187 · Post by **Hawke187** » Tue May 23, 2006 12:21 am

OK,
this is something I am sure at least one of you has delt with in the past...

My latest aquision a 78 spider , the water temp gauge will within a in or two will quicky rise to the 190 range and then as it comes off the choke it will read right at red line..

I checked the temp at the head right at the sensor with an infared thermo and it reads 200 +/- 5, and the rediator reads right around 190.

The fan operates normaly, cycling on and off when in traffic, but the gauge always stays right around red line...

I checked the overheat sensor switch and it operates normal, grouning it causes pegged needle, and the temp sensor will do the same when grounded.

I am not sure if this is a problem with the sending unit , gauge or a notorious ground issure?

I have not been able to tear into it much as my job has had me in the work, sleep, repeat routine, but I am coming into my days off and and information would be good as to help narrow it down.

Thanks in advance.

mvizzina · Post by **mvizzina** » Mon Jun 12, 2006 9:08 pm

My 85 Spider does something very similar. My temp will be completely normal and then suddenly the needle will bury itself past 260. It's quite alarming as I'm driving along. I've come to realize now after several incidents that it is a false reading. In about a minute the needle will instantly jump back down to the correct temperature. I can't forcibly duplicate the problem so I have to wait until it randomly happens before I can try and troubleshoot it. I've fiddled with several things when it does and nothing ever seems to have an effect... that is until the last time it happened. This is going to sound crazy but when it happened the last time, I switch on and off my headlights and the temp gauge immediately went back to normal. I don't think it was a coincidence. The problem must be rooted in something electrical. Please let me know what you find.

spiderrey · Post by **spiderrey** » Mon Jun 12, 2006 9:58 pm

could be a bad switch, or the wire is grounding out somewhere. i was driving my 68 a while ago, everything was fine. cruzing down the fwy, i happened to glance at all the gauges. the temp was buried in the red. i pulled over right away. poped the hood and found the top of the sensor had broken off and grounded out on the head. when i removed the wire i got a correct reading. what a relief, i was to far from home to deal with any real trouble

So Cal Mark · Post by **So Cal Mark** » Tue Jun 13, 2006 2:02 am

try cleaning all of the fuses and contacts in the fuse box and clean and tighten all grounds

Mad-Machine · Post by **Mad-Machine** » Tue Jun 13, 2006 10:05 am

an air bubble in the head can do the same thing.. superheated steam can make the sensor read high.

FMO · Post by **FMO** » Wed Jun 14, 2006 7:15 am

I had the same problem, used a lot of time to try to find out what the problem was. Then I bleed the cooling system, and now the temp gauge never raise past 190

mvizzina · Post by **mvizzina** » Thu Jun 15, 2006 11:30 pm

How difficult would you say it is to bleed the cooling system. What's involved in it and what tools would I need? Thanks.

So Cal Mark · Post by **So Cal Mark** » Fri Jun 16, 2006 12:47 am

it's not that hard, and you don't need any special tools. If your car is carbed, fill the cooling system, then remove one of the choke heater hoses and finish filling the cooling system thru that small hose until no more air bubbles come out of the radiator. Then install the rad cap and fill thru the small hose until water comes out of the choke nipple.

If your car is FI, use the small hose on top of the throttle body with the same procedure.
You can also install a flush tee in the heater hose where it passes over the exhaust cam cover and then finish filling the system there

perthling · Post by **perthling** » Fri Jun 16, 2006 12:49 am

I find that jacking the front of the car quite high so that the radiator cap is the highest point achieves the same result. Do take time to squeeze your hoses though to dislodge any trapped air inside the block.

Hawke187 · Post by **Hawke187** » Wed Jun 21, 2006 4:38 pm

Well good news, I visted with a local Fiat Guru, and with quick flick of the wrist he cured the problem in 2 sec flat...........

(Made me feel like an ID 10 T...)

I had gone through all the components individualy, except....

The 2 sensors, the gauge temp sensor was working perfect all the time, it was when the temp over heat sensor was plugged in at the same time as the Gauge sensor, it read high, very high.....

He knew right away, as I am a new owner to this Fiatsco, he say there are 2 possiblities, (1) the overhat sensor swith is not a switch type, but another gauge type (or just the plain wrong one...) ...Or... (2) the overheat swith is indeed bad, as I am a gauge watcher, he said it is not even needed, so one 2c piece of electrical tape to seal the overtemp sensor and I was back on the road, running cool and no more worries... Whew....
While he was under the hood he tweeked the carb a bit and now she is running smoother as well...

Grand total for this expert troubleshooting??? a hand shake and a smile...

I then bought the gaskets for the in block thermostat, which is one thing I came for and was out the door for just over $2..., after a good half hour of usefully BS'ing, Dam thats what expert service should be like....
I'll be back....... even though it is a good 3/4 hour drive through down town Denver traffic...
And yes I told him about this Forum and hope to see him online soon....

Well at least thats fixed now... with temps reaching into the 100's here it is nice to know it is only me overheating, not the car.....

kimu · Post by **kimu** » Thu Jun 22, 2006 2:50 pm

I will in Denver on Monday and need to pickup a part (rad fan switch) from him.. Care to share his contact info?

Many thanks...

Hawke187 · Post by **Hawke187** » Fri Jun 23, 2006 11:05 pm

Sent you a PM with his details.