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Old 07-24-2018, 03:53 PM   #1
saxart
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190deg Therm causing temp gauge to read high?

Quick question. I just got the crate engine in my 70 up and running. The temp gauge is all but pegged even though a hand held laser therm shows the therm hosing to be in the 190-200deg Range. I got the correct sending unit from Lectro Limited (mounted In Drivers side head) and made sure the gauge cluster was properly grounded. I even put a ground pigtail on the backside of the gauge itself. Could the 190 deg therm be causing this higher reading on the gauge?
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Old 07-24-2018, 04:00 PM   #2
Ol Blue K20
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Re: 190deg Therm causing temp gauge to read high?

I believe it can. If my memory serves me correctly the factory thermostat was165 degrees. Back in the day 210* was panic time.
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Old 07-24-2018, 05:27 PM   #3
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Re: 190deg Therm causing temp gauge to read high?

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Originally Posted by saxart View Post
I got the correct sending unit from Lectro Limited
I had similar issues using a 190 degree thermostat and standard off the shelf temperature sending unit. However, the issue was resolved by purchasing and installing a correctly calibrated temp sending unit for a 72 Chevy 350 from Lectric Limited.

Perhaps Lectric Limited (assuming that's who you purchased the temp sending unit from) could provide assistance if you call them and ask fornhelp.

Also, to my understanding, these engines were designed to run with 190 degree thermostats. Running a lower than specified thermostat would mask the underlying issue.
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Old 07-24-2018, 06:09 PM   #4
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Re: 190deg Therm causing temp gauge to read high?

My truck was reading a pegged gauge with no symptoms of running hot. I put a different (mechanical) gauge in, and it runs about 190, so I suspect that something could be wrong in your factory gauge circuit. Check you routing and see if the wire is grounded somewhere between the sender and the cab. Maybe something got pinched.
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Old 07-24-2018, 08:55 PM   #5
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Re: 190deg Therm causing temp gauge to read high?

Shot in the dark: do you have a good ground strap from the block to the frame? Can't have too many grounds, especially when your sender is in the head.
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Old 07-24-2018, 10:11 PM   #6
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Re: 190deg Therm causing temp gauge to read high?

I believe the temp gauges and thermostats are tuned to each other. By that I mean a gauge is designed to be used with a certain * thermostat range to read properly. I ran into the same situation with an 85 Blazer some years ago. The gauge always registered normal until I put in a hotter thermostat. The temp gauge showed full hot in 3 minutes of idling. The engine was not hot but the gauge said it was. I put the stock thermostat back in and the gauge read right.
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Old 07-25-2018, 01:53 AM   #7
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Re: 190deg Therm causing temp gauge to read high?

Stock thermostat was 190*. The 190* thermostat was to reduce emissions. Therefore, it should not be a factor.
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Old 07-25-2018, 07:14 AM   #8
clay68c10
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Re: 190deg Therm causing temp gauge to read high?

I had the same problem, I changed the resistor on the back of the gauge to get the reading where I wanted it. I don’t remember what ohms value did the trick.
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Old 07-25-2018, 08:24 AM   #9
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Re: 190deg Therm causing temp gauge to read high?

190 is mighty close to 212, so I'd say the gauge is reading correctly. Your truck is close to boiling and that's what the gauge is reading, pegged = boiling/212. 190 is too high. I always run 180 and have no issues.
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Old 07-26-2018, 04:24 PM   #10
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Re: 190deg Therm causing temp gauge to read high?

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190 is mighty close to 212, so I'd say the gauge is reading correctly. Your truck is close to boiling and that's what the gauge is reading, pegged = boiling/212. 190 is too high. I always run 180 and have no issues.
Water at sea level boils at 212 degrees F. Water mixed with anti-freeze and under pressure (our trucks should have at least a 15lb pressure cap) wouldn't boil until a much higher temperature is reached.
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Old 07-29-2018, 03:47 AM   #11
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Re: 190deg Therm causing temp gauge to read high?

Ive seen a lot of new parts that are junk!! That new sending unit is probably made in good ole China. Just sayin
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Old 07-29-2018, 07:40 AM   #12
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Re: 190deg Therm causing temp gauge to read high?

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Water at sea level boils at 212 degrees F. Water mixed with anti-freeze and under pressure (our trucks should have at least a 15lb pressure cap) wouldn't boil until a much higher temperature is reached.
You are correct. Regardless, 212 is only 22 degrees above 190 so gauge will read close to 212 before thermostat opens.
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