Engine Temperature reading is not working properly

ggradtech · Jan 30, 2020

My 351w engine has a temperature reading issue. Just today, it is spiking at 210, going down some, and going up again. It’s not accurate though. My fan probe activates the fans to come on at 180, and that is working perfectly. Could the temperature sending unit that is threaded into the upper intake be the culprit? I hope it’s this and not a wonky gauge in the dash panel. Thanks

General karthief · Jan 30, 2020

More likely your thermostat, stock gauge?
JMO

jrichker · Jan 30, 2020

ggradtech said:
My 351w engine has a temperature reading issue. Just today, it is spiking at 210, going down some, and going up again. It’s not accurate though. My fan probe activates the fans to come on at 180, and that is working perfectly. Could the temperature sending unit that is threaded into the upper intake be the culprit? I hope it’s this and not a wonky gauge in the dash panel. Thanks

From what I have seen, that is an indication of a low coolant level. Some of the other guys may want to chime in and give you some advice on burping the coolant system.

General karthief · Jan 30, 2020

Good catch joe!
Do you have a coolant recovery tank?
Some use a Lisle funnel, I jack up the front of the car as high as I can when refilling the radiator, squeeze the lower hose as I fill it.

ggradtech · Jan 30, 2020

I’ll certainly check my coolant level. The thing is though, when the engine is not HOT, it reads like 210. It goes up a little and back down. The temp probe is a 180* one. The fan does come on at about what “seems like” it’s at 180ish or so. This is why I figure it may be something with the sending unit or possibly the gauge in the dash.

General karthief · Jan 31, 2020

Just get an aftermarket gauge, you can mount it on the bottom of the dash or in the engine compartment even if just temporary.
you could get an infrared thermometer pretty cheap and compare readings. Compare it to the stock gauge readings.

ggradtech · Jan 31, 2020

The gauge is an aftermarket one. This morning it’s pretty cold out. I started driving and it stalled under 150 for a while, then went to 180 for a bit. Then, all of a sudden, it was bouncing between 180-250 and back and forth. Then it stayed at 250, so I immediately drove to my garage. I cycled the key a few times, but it stayed pretty hot. Maybe 230 or so. The fans were on as well, but they are triggered to go on at 180. Maybe once it’s cool again, I should run the motor until warm/hot with the radiator cap off to check and see that the water pump is cycling water through the radiator fins?

ggradtech · Jan 31, 2020

Also, the lower rad hose wasn’t all that hot to touch, but the upper was tight and pretty hot to touch.

General karthief · Jan 31, 2020

Thermostat.
Just my opinion and not base on any actual mechanical experience.

ggradtech · Jan 31, 2020

Sounds like I’ll remove it and replace the thermostat. It’s weird though that I just had my intake resealed last week and also a new t-stat housing installed. Maybe the new (assuming new) t-stat is bad?

90sickfox · Jan 31, 2020

What kind of fans are you using ? I use Ford Contour fans on my tubo fox with no issues...temp stays around 202....192 degree thermostat.

ggradtech · Jan 31, 2020

Same here. Contour fans. I only had this issue pop up in the last day or so. I did have my intake resealed recently. I’m gonna take some infrared gun readings too just to confirm it’s not a wonky gauge or sending unit.

jrichker · Jan 31, 2020

@ggradtech

Testing the thermostat:
Buy a cooking thermometer from Walmart its about ~$10 or so; be sure that it goes over 200°. Put a pot of water on the stove and turn the heat on high. Put the thermostat and the thermometer in the pot; watch the thermostat open as the water heats up. If it isn't wide open by 210 °, you have a problem.

Blown88GT · Jan 31, 2020

After 32 years my temp sending unit was reading much lower than normal.
Replaced the $10 unit & all was normal.

ggradtech · Jan 31, 2020

So I ran the car today. While cold, I uncapped the radiator and let it come up to temperature. Once it got decently warm, I noticed some big air bubble burps. I then recapped the radiator and took it for a few mile drive. So far, Im thinking it may have had some air trapped in the cooling system. Maybe the air pocket purge cured it?

General karthief · Jan 31, 2020

time will tell.

2000xp8 · Feb 1, 2020

When it spikes like that, it's most likely air in the system.
The thermostat isn't going to cause a spike, overheating, yes, but it doesn't open and close fast enough for you to instantly see it on a gauge.

Engine Temperature reading is not working properly

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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wonder how much it would cost to ship you a pair

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