1990 Mazda b2600 Overheating

1990 MAZDA B2600
180,000 MILES • 2.8L • 4 CYL • 4WD • MANUAL
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95BEAR
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The truck will run at about half temp when going. Takes about 2 miles to get that hot. If I turn it off then back on it will read about 3/4 if not a bit more. Replaced the fan clutch, thermostat, changed oil and radiator flushed. What can it be?
Sep 22, 2014 at 11:57 AM
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KHLOW2008
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Do you have coolant loses?
Is the gauge accurate?
Sep 22, 2014 at 1:12 PM
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95BEAR
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Gauge is right. Nothing is showing on the ground when it comes to coolant.
I should note that there is a small exhaust leak. Coming from the manifold into the piping its missing a donut.
Sep 22, 2014 at 8:51 PM
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KHLOW2008
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Did you check the coolant level when engine is cold and what does it show?
Sep 23, 2014 at 8:56 AM
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95BEAR
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Both the reservoir and radiator are filled. Checked with 3 different mechanics on that. And the fan, thermostat and radiator had to be done anyway.
Sep 23, 2014 at 10:49 AM
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KHLOW2008
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At temperature reading of 3/4, is the coolant showing signs of overheating?
Does the reading changes when the engine is started and running?

Sep 28, 2014 at 2:26 AM
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95BEAR
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The temp does change. I can start it and run it a few miles and it will hit 1/2. Before this problem it ran under half at about 1/3. Then after I let it sit for an easy 30min and start the truck up the temp will read 2/3 to 3/4.

The coolant does show signs of heating up. Sometimes it will push out of the radiator into the reservoir while boiling. Only ever back flushes maybe 1 of 8 times.
Sep 28, 2014 at 8:05 AM
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KHLOW2008
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How is the condition of the radiator cap? If it is not new, try replacing it .
Sep 30, 2014 at 9:48 AM
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95BEAR
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The cap is new and there is no leak under it where it would commonly crack and leak.
Oct 4, 2014 at 7:47 PM
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KHLOW2008
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The only thing left to check would be the water pump. It could be weak due to worn impeller.
Oct 6, 2014 at 8:57 AM