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Joe palka

R model running warm but idles normal

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i have a 1989 RD688s believe it's the e7 with a 9 speed. the truck was idling and running around 190 - 195. after changing the thermostat and the water/coolant filter, it now idles at 180, but when running the truck both empty and loaded it makes its way back up just under 200. Another issue to screw things up is the red warning temp light above the gauge seems to go on at 150. then sometimes at 180. then on and off around 190. so it dosent stay too consistent. that light is all over the place. now with a temp gun the motor seems to be a few degrees cooler then the gauge which I'm sure could be normal. Im just debating on which route to go next as i chase this issue before the warm weather comes. But im looking to hear anyone's thoughts and maybe past experience. i appreciate any help. thanks.

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Could be a faulty gauge I have had this experience in past. If changing filter lowered your temp you may want to flush your rad. Sounds like your not getting a good flow.

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yea we're definitly going to replace the gauge, and i agree with you on the bad flow. thanks alot for your input man

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Had a DMM come in with a solid core once. Could not get a rod through any of the core galleries. Installed a new core and reused the tanks. good2go.   

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literally just got done putting in a new sending unit to the gauge and checking the temp now. hopefully it's allright but if not then I may be heading in the radiator direction. thank you for your help and input

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Your thermostat should have had a bleeder or vent that goes to the top for venting air in the water manifold.Check that

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the sending unit was definitly bad. but unfortunatly it wasn't 100% of my issues. its showing alot better on the gauge. she's staying just under 180 when idling and running around 180 but when heavy in the pedal it climbs just under 200. but then makes it's way right back to 180 when idling for just a couple minutes. so something still isn't right but we're making progress and i will check for that bleeder this weekend.  thank you for the help and knowledge guys 

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that sounds about right. running hard (hot) let off and it cools down...normal
Can you hear the fan kick on?

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5 hours ago, Joe palka said:

the sending unit was definitly bad. but unfortunatly it wasn't 100% of my issues. its showing alot better on the gauge. she's staying just under 180 when idling and running around 180 but when heavy in the pedal it climbs just under 200. but then makes it's way right back to 180 when idling for just a couple minutes. so something still isn't right but we're making progress and i will check for that bleeder this weekend.  thank you for the help and knowledge guys 

That is normal.

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