Home » Public Forums » GMCnet » Temp fluctuation after rebuilt engine and radiiator (Okay, this is a question for the headstrong. Following an engine rebuild at one of the majors in the GMC community, we're experiencing a temp flucuation on our gagues.)
| Temp fluctuation after rebuilt engine and radiiator [message #226617] |
Tue, 22 October 2013 17:12  |
MichaelP
Messages: 65
Registered: October 2012
Location: Ohio
Karma: 0
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So, after an engine rebuild at the co-op, we're experiencing a inordinately high (according to our gauge)temp reading -- running at about half, rather than the 1/4 it was running before the work. Oddly enough, it seems to drop when I accelerate up a hill, and climb when I run steady. I'm currently thinking we're having some sort of transmission anomaly, where, perhaps, our third gear is struggling to shift, causing the engine to heat up, ad when I finally push it to forth, it cools down (just a thought, of course). We're about to jump off on a cross country trip, and further diagnostic at a gmc specialist seems overkill at this point. Anyone have any ideas?
[Updated on: Wed, 23 October 2013 11:44] Report message to a moderator |
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| Re: [GMCnet] Temp fluctuation after rebuilt engine and radiiator [message #226619 is a reply to message #226617] |
Tue, 22 October 2013 17:25  |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Should upshift to second about 12-14 MPH. Should upshift to 3rd about 28 -
30 MPH. There is no 4th in a GMC TRANSMISSION. If your shift points are
higher than this, you either have a vacuum line off the transmission
modulator or a failed modulator. Could be other stuff as well, but start
here first. It is not unusual for a newly rebuilt engine to run hot the
first few thousand miles. I did not say overheat, there is a difference.
Check also your electrical connections on the gage sending unit. That stuff
can get damaged during overhaul.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Oct 22, 2013 3:12 PM, "Michael Pisano" <mapisano@gmail.com> wrote:
>
>
> So, after a couple thousand dollars and an engine rebuild at the co-op,
> we're experiencing a inordinately high (according to our gauge)temp reading
> -- running at about half, rather than the 1/4 it was running before the
> work. Oddly enough, it seems to drop when I accelerate up a hill, and
> climb when I run steady. I'm currently thinking we're having some sort of
> transmission anomaly, where, perhaps, our third gear is struggling to
> shift, causing the engine to heat up, ad when I finally push it to forth,
> it cools down (just a thought, of course). We're about to jump off on a
> cross country trip, and further diagnostic at a gmc specialist seems
> overkill at this point. Anyone have any ideas?
> _______________________________________________
> GMCnet mailing list
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226620 is a reply to message #226617] |
Tue, 22 October 2013 17:35 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Before you get carried away with diagnosing the issue, check that the gauge and sending unit are not the problem. Check the electrical connections and the grounding of the aluminum plate that the gauge is mounted in. Replace the temperature sending unit. It might also be worth you time to verify the operating voltage of the alternator while the gauge is changing readings.
After that you might install a mechanical gauge.
If the two gauges agree, then it is time to start believing that you actually have a cooling problem of some kind.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226625 is a reply to message #226617] |
Tue, 22 October 2013 18:22 |
Otterwan
Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...
Karma: 0
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| Momo wrote on Tue, 22 October 2013 15:12 |
So, after a couple thousand dollars and an engine rebuild at the co-op, we're experiencing a inordinately high (according to our gauge)temp reading -- running at about half, rather than the 1/4 it was running before the work. Oddly enough, it seems to drop when I accelerate up a hill, and climb when I run steady. I'm currently thinking we're having some sort of transmission anomaly, where, perhaps, our third gear is struggling to shift, causing the engine to heat up, ad when I finally push it to forth, it cools down (just a thought, of course). We're about to jump off on a cross country trip, and further diagnostic at a gmc specialist seems overkill at this point. Anyone have any ideas?
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Did you replace the thermostat? We had a sticky one, and it reacted pretty much as you describe. It would run hot until we pushed the engine hard, then run cool because the increased heat had caused it to open.
1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226634 is a reply to message #226617] |
Tue, 22 October 2013 20:04 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Common practice is to replace the OEM temp sender that read very low and was misleading, with a more sensitive sender where close to half scale is normal operating temp. The OEM scale caused some cooked engines while not reading that high. Did you ask Jim B if they put in a new sender and where it should be reading? Is all the air out of system and at least half full in overflow tank?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226635 is a reply to message #226617] |
Tue, 22 October 2013 20:06 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| Momo wrote on Tue, 22 October 2013 15:12 |
So, after a couple thousand dollars and an engine rebuild at the co-op, we're experiencing a inordinately high (according to our gauge)temp reading -- running at about half, rather than the 1/4 it was running before the work. Oddly enough, it seems to drop when I accelerate up a hill, and climb when I run steady. I'm currently thinking we're having some sort of transmission anomaly, where, perhaps, our third gear is struggling to shift, causing the engine to heat up, ad when I finally push it to forth, it cools down (just a thought, of course). We're about to jump off on a cross country trip, and further diagnostic at a gmc specialist seems overkill at this point. Anyone have any ideas?
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Was the temp gauge sending unit replaced during the rebuild? If so, the aftermarket (Napa, Standard Ignition, etc.) senders read hotter than the OE sender. It might not be running hotter, just reading hotter. If you have an IR thermometer, shoot the thermostat housing and see what it says.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226653 is a reply to message #226634] |
Tue, 22 October 2013 22:06 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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| JohnL455 wrote on Tue, 22 October 2013 20:04 |
....Is all the air out of system and at least half full in overflow tank?
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Really a key question imo. Air in the system will act as you describe.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: [GMCnet] Temp fluctuation after rebuilt engine and radiiator [message #226684 is a reply to message #226617] |
Wed, 23 October 2013 07:30 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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What Jim said. If that vacuum line is off, or any vacuum line for that
matter, you could be running hot and the vacuum modulator on the trans will
act up also.
.
Steve F.
On Tue, Oct 22, 2013 at 3:12 PM, Michael Pisano <mapisano@gmail.com> wrote:
>
>
> So, after a couple thousand dollars and an engine rebuild at the co-op,
> we're experiencing a inordinately high (according to our gauge)temp reading
> -- running at about half, rather than the 1/4 it was running before the
> work. Oddly enough, it seems to drop when I accelerate up a hill, and
> climb when I run steady. I'm currently thinking we're having some sort of
> transmission anomaly, where, perhaps, our third gear is struggling to
> shift, causing the engine to heat up, ad when I finally push it to forth,
> it cools down (just a thought, of course). We're about to jump off on a
> cross country trip, and further diagnostic at a gmc specialist seems
> overkill at this point. Anyone have any ideas?
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Take care,
Steve
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226755 is a reply to message #226617] |
Wed, 23 October 2013 16:42 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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That sounds like air in the system. Be sure the radiator cap is new, clean and a 9 PSI unit and fully tightened to the stop tabs. Also be sure the hose to the over flow tank is not old, loose cracked or perforated and the tube is submerged. Shoot the thermostat neck to get a reading NOT the radiator... Won't tell you much that way.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Temp fluctuation after rebuilt engine and radiiator [message #226758 is a reply to message #226747] |
Wed, 23 October 2013 17:10 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Sir: Old wires do not like engine and tranny R&Rs. Kinda sounds like a pinched or mashed or rerouted wire from instillation. I found one on a scooter last week where the coil wire had been taken off and put back on in a different configuration and the wire was broke inside the insulation. Would start up and run about 1 mile then die. Would restart only if I pushed on the wire. Also might suspect a bad ground from engine to battery - or battery - to dash.
| Momo wrote on Wed, 23 October 2013 15:55 |
Yeah, I think our gauge is not trustworthy. Happened again just now, turned of the ignition and the gauge spiked from 1/4 to past hot as soon as I turned the key off.
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C. Boyd
76 Crestmont
East Tennessee
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