Under Heating?

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bartigue
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Re: Under Heating?

Post by bartigue » Sun Apr 15, 2018 7:37 pm

If the fan isn’t ever turning off then things are either way too hot or the fan switch is bad. One way to test the former is to disconnect the fan and drive it, if it stays steady while driving air through the radiator then your thermostat is likely ok.
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Re: Under Heating?

Post by rridge » Mon Apr 16, 2018 9:31 am

Giulio,

As Bradley suggests, the next step is to take the car on the road. With temps in the 70's to low 90'sF and the engine up to 185, the fan should run when you come to a stop for a light but should cycle off as soon as you are up to a steady cruising speed. If gauge temp continues to rise as you drive at say a steady 40mph, there is a problem with the cooling system, such as a silted up radiator, collapsing lower radiator hose, or perhaps just a slipping accessory belt. The fan and its sensor are not the culprits.

The dash temp gauge has inputs from two sensors in the head. This is a feature unique to Spiders and a clue to the cooling challenges of its sloping nose and limited grill opening. One head sensor provides the actual temp signal. The other is simply an on/off switch. When the head temp approaches the overheating point, normally about 230, the switch turns on and sends a signal to peg the gauge needle in the red zone.

Both senders screwed into bosses on the top of the head between spark plugs. One is in the center of the head. The second is towards the back. Each has a boot over it with a single wire emerging through the boot top. Which sender is in which position varies from car to car. Lift the dark rubber boots off and pull the spade connectors off one and then the other and observe the gauge reaction.

The one that does not send the temp needle back to zero when disconnected is the overtemp switch. Leave it off for the rest of the testing. Clean the spade connections on the senders while there. They are resistance circuits.
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Re: Under Heating?

Post by GiulioT81 » Mon Apr 16, 2018 2:22 pm

OK. Thanks guys.

I didn't know what that second sensor was for. I'll see which is which and will let you know what I find.

With regard to fan operation in current condition, it will stay on while driving until dash temp gauge gets to a 170/175 temp range. And will usually run a couple of minutes after I shut car off.

GT
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Re: Under Heating?

Post by GiulioT81 » Tue Apr 17, 2018 7:30 pm

Hi.

So I did the unplug the fan test when I took my daughter to ballet class.

Outside temp 69.
Distance to destination is 6 miles, on mostly 2 lane 45 mph country roads, with a couple of stop signs.
Did not remove temp sensor connectors.

Car ran with needle on the "1" of "190" type for most of the ride once it reached temp.
Stopped at "rush hour" stop sign for about 3 minutes. Needle stayed between the "1" and "9" most of that time, then started to rise to the "0" before I started moving. Temp lowered to the "9" within the last mile of the trip.

Dropped off daughter. Car still on.

On the way back, the temp kept lowering until the needle was just to the left of the "190" and never touched it until I got back into my neighborhood (25mph roads). I idled in my driveway for about a minute, then shut the engine off when needle was on "9".

So in the 22 minute/12 mile drive, the engine never went over the "0" of "190" with the fan unplugged.

Is my thermostat sticking, which is keeping the radiator hot enough for the fan to stay on?

Thanks!

GT.
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Re: Under Heating?

Post by rridge » Tue Apr 17, 2018 8:04 pm

If the gauge is correct, the cooling system and thermostat are functioning normally. The fan is not.
Richard
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Re: Under Heating?

Post by GiulioT81 » Tue Apr 17, 2018 9:21 pm

Hmmm. So the engine thermostat is not staying open too long? The car has never run so cool. It always ran on the 190 line. Doesn't it run richer when it runs cooler?

Repeated the test again when I went to pick up my daughter 2 hours later, 67 degrees with lights on.

Interesting observation: Temp needle jumped up the thickness of the needle when I put my lights on.

She ran essentially the same, except there wasn't as much traffic and needle was directly on the line over 190, until I got to my destination. Engine off for 15 mins, then repeated what it did on the ride back last time, with cooler running temp to the left of the "1" in "190".

Thanks RR

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Re: Under Heating?

Post by 81-SPIDERMATT » Tue Apr 17, 2018 9:57 pm

Does it take longer to heat up to operating temp... sounds like a thermostat stuck open to me ... Matt
It's not an oil leak...that's power sweat

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Re: Under Heating?

Post by GiulioT81 » Wed Apr 18, 2018 12:12 am

NO 81, she comes up to temp fine. It's after temp starts to rise above 190.

GT
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Re: Under Heating?

Post by rridge » Wed Apr 18, 2018 8:30 am

The engine running at 190-195 is normal. The fan running for a few minutes after shutdown is normal on a warm day for a late Spider. Temp gauge shifting slightly when headlights are switched on is normal. Fan running continuously while driving or continuing to run after temp has fallen to 180 is not normal. Old temp gauge showing flakey readings is pretty common. Temp gauge showing flakey readings due to a bad overtemp sender is very common. Some dirty contacts and poor grounds in the electrical system of a 40 year old car are almost guaranteed.

FI system has its own temp sensors, one on top of the coolant tee and one inside the AFM. The FI designers didn't trust the gauge circuit either. They are unrelated to the two temp sensors on top of the head. Redundancy is not always the answer to reliable service.
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Re: Under Heating?

Post by GiulioT81 » Thu Apr 19, 2018 12:24 am

OK, but my car doesn't appear to be running at 190-195. When I tested the temp with a hand held to the top of the head it read 181 while the dash meter read 190. I replaced the sensor at the coolant tee a few years ago. Where is the sensor in the AFM. Is it connected to the outside of the AFM?

This has become a little annoying. What do you think I should I test next?

Thanks.

GT.
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