Fluctuating Temp gauge

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Apr 13, 2020 | 01:22 PM

Chris754

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Joined: Jan 2018

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Fluctuating Temp gauge

89 f250, replaced water pump, now when the engine is cold and i get in and drive the temp gauge goes about 3/4 of the way then drops drastically down to 1/4 of the way on the gauge. then it will fluctuate between the n and the o on the normal range.
replaced the coolant temp sensor today fixed nothing. i have heat in the truck.
also tired burping cooling system, still having this problem
any suggestions?
thermostat worked fine before

Apr 13, 2020 | 02:22 PM

Freightrain

Lead Driver

Joined: Jan 2003

Posts: 9,893

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From: Ohio

The thermostat may have worked fine before, but that never guarantees it won't fail tomorrow. That is unless there is still an air pocket in the system.

Apr 13, 2020 | 03:20 PM

torq'ta 5 8

Lead Driver

Joined: Jan 2019

Posts: 5,067

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From: N.W. Alabama

what temp thermostat does it have, while driving mine, it will go between the n and o on normal, which is fine, when you first start yours up does it sound like a baby huey is taking off? if not you can check how easy/hard fan is to turn, with engine off and keys in pocket.

Apr 13, 2020 | 04:05 PM

Conanski

FTE Legend

Joined: Jun 2006

Posts: 31,930

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From: Ottawa, Ontario

Does it have an oversized rad in it.. as in a 2 core vs the factory 1 core? If so then it has a bit too much rad for the motor now in anything but the hottest climates.

Apr 13, 2020 | 06:52 PM

Chris754

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has a 195 degree, i also replaced fan clutch when i did water pump forgot to mention.

Apr 13, 2020 | 06:57 PM

Chris754

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it has a 2 core rad
i am thinking maybe it is the other thermostat temp sensor between the intake manifold and the valve cover?

Mar 31, 2021 | 11:02 PM

PRIMERED79 SHORT BED

Laughing Gas

Joined: Jan 2012

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Did you ever get this figured out?
I have been trying to get this solved in mine for yrs now, but I do have the 2 row rad maybe I should try a one row rad?

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Apr 1, 2021 | 09:00 AM

rexf

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Joined: Oct 2020

Posts: 63

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From: Texas

Quote:

Originally Posted by PRIMERED79 SHORT BED

Did you ever get this figured out?
I have been trying to get this solved in mine for yrs now, but I do have the 2 row rad maybe I should try a one row rad?

Quote:

Originally Posted by Chris754

the thermostat is nearly always the problem for a fluxuating water temp if the sensors are good, there are 2 temp sensors, one for ECU and one for the guage cluster, which one did you replace?
I have a 3 core aluminum rad because of my humid climate with towing in nearly stand still traffic or highway in 90F degrees, even without a load it always gets to temp in a good time and have never seen it fluxuate
when bleeding the system, how did you do it? i have a "no-spill" radiator funnel kit pretty cheap from amazon which made it really easy, i pulled on a hill so all the air would go to the funnel, i can safely say there is 0% air in my system now, and it works great!
btw i have a 195F degree thermostat