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#1 |
Registered User
Join Date: Jul 2007
Location: Turlock,CA
Posts: 31
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1979 GMC 1/2 Ton No Oil Pressure
I recently bought a 1979 GMC 1/2 ton, short bed, 2wd, 350 that the previous owner parked 8 years ago due to what he thought was a collapsed lifter. I have the truck running again but there is no oil pressure at anytime. Would no oil pressure at any temp or speed mean the oil pump is bad or a bearing failed?. It does have a lifter tick but I'm sure that due to lack of oil
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#2 |
Registered User
Join Date: Nov 2015
Location: Alberta
Posts: 464
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Try a filter change A few weeks ago our 2008 with a 5.3 had no oil pressure and a pile of top end noise. The filter was all collapsed and the paper element was sucked in. I switched brands and did an oil change just like new now. Maybe try a good thick oil. I wouldn't run a super thick oil daily but maybe see if your needle will jump a little with it. Try cheapie mechanical gauge too as a back up
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-Cody |
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#3 |
Registered User
Join Date: Jul 2007
Location: Turlock,CA
Posts: 31
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Re: 1979 GMC 1/2 Ton No Oil Pressure
I changed the oil and replaced the Fram filter with a AC Delco filter. I also added Seafoam to the oil
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#4 |
Registered User
Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,540
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Pull one of the valve covers and see if you have oil coming out of the pushrods with the engine running. It is a bit messy but will confirm if you have oil flow or not. Gauges do go bad. Probably need new valve cover gaskets anyway.
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#5 |
Registered User
Join Date: Oct 2009
Location: Buhl, Idaho
Posts: 1,438
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Have you tried a different gauge? I would throw a mechanical one on there first. Does the motor knock? If it had no oil pressure, you would have damage very quickly.
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86 c30 crew cab dually 454/400 4/6 drop SOLD 1-8-11 1981 chevy K10 short Bed Scottsdale SOLD 10-26-2020 67 GMC Stepside Straight six/3 on the tree "The Peach" 2020 Silverado Double Cab LT Z71 5.3 8 speed Daily Driver K10 build http://67-72chevytrucks.com/vboard/s...d.php?t=671934 The Peach build http://67-72chevytrucks.com/vboard/s...d.php?t=733903 ![]() |
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#6 |
Registered User
Join Date: Oct 2015
Location: Waskatenau, Alberta
Posts: 259
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Im leaning toward a bad sending unit/wire to the sending unit or gauge. If your oil pump is not working or the pickup tube fell off, the engine would "knock", than seize. This doesn't take long to happen. What did the original oil look like when you drained it? I have seen guys run engines until the oil turns into grease, blinding the screen on the pickup tube. Usually even a very worn engine will show a little oil pressure cold.
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#7 |
Registered User
Join Date: Jul 2007
Location: Turlock,CA
Posts: 31
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Re: 1979 GMC 1/2 Ton No Oil Pressure
I will pull the valve covers and check flow. I have not tried a mechanical gauge on it yet but the motor does have a ticking sound coming from the top end. The oil in it was black and looked like 20w50 or thicker
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#8 |
Registered User
Join Date: Jun 2015
Location: PA
Posts: 441
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Re: 1979 GMC 1/2 Ton No Oil Pressure
the current gauge may not even be hooked up
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#9 |
Registered User
Join Date: Jul 2007
Location: Turlock,CA
Posts: 31
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Would a stuck by pass valve on the oil filter housing cause zero oil pressure?
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#10 |
Registered User
Join Date: Oct 2015
Location: Waskatenau, Alberta
Posts: 259
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Re: 1979 GMC 1/2 Ton No Oil Pressure
I'm pretty sure the bypass valve just routes oil around a plugged filter.... shouldn't prevent oil pressure. (but I could be wrong) I have never had a filter on long enough to plug up. 79's had the "electric" sending unit. Have had trouble with these in the past. Of course its not easy to get at. Pretty well have to lay on the engine to reach.
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#11 |
Registered User
Join Date: Jul 2007
Location: Turlock,CA
Posts: 31
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Correct me if I'm wrong but if the truck had no oil pressure wouldn't the dipstick still read full with it running?
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#12 |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,951
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Can't tell what it'll read with the engine running. The crank counterweights stir up the oil in the pan. That's why racing and modern engines have windage trays just under the crank to keep the oil from getting blown onto the crank and creating drag.
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1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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#13 |
Registered User
Join Date: Nov 2015
Location: Alberta
Posts: 464
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Re: 1979 GMC 1/2 Ton No Oil Pressure
On my truck it did show no oil pressure when the filter sucked up and closed. I thought that the bypass just pumped unfiltered oil to engine. I thought maybe it bypassed the sending unit too but definitely had no oiling with the noisy lifters. Wish I took a pic of the filter. It was the GKI brand.
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#14 |
Registered User
Join Date: Nov 2015
Location: Alberta
Posts: 464
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Whoops quoted wrong guy
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-Cody |
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#15 | |
Registered User
Join Date: Nov 2015
Location: Alberta
Posts: 464
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Quote:
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-Cody Last edited by Gmc.guy; 02-14-2016 at 07:38 PM. |
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#16 |
Post Whore
![]() Join Date: Aug 2014
Location: Sacramento, CA
Posts: 10,827
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Re: 1979 GMC 1/2 Ton No Oil Pressure
couple weeks ago my truck stopped showing any oil pressure yet it runs great, I also changed the oil and oil filter after this happened yet that did not fix the problem so I am wondering if the OP ever figured this out and what was it?
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#17 |
Registered User
Join Date: Dec 2011
Location: Regina, SK, Canada
Posts: 622
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Same happened to me, it was the sending unit.
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1979 Chevy Dually Crew 4X4 454, D60 Tru-trac, D70 Detroit Locker, 3.73, 4L80E/NP205 1971 GMC 3/4 Ton 4X4 |
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#18 |
Registered User
Join Date: Nov 2015
Location: portage wi
Posts: 504
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Oil pump failure is not very common(it runs in oil) and when it does happen it usually fails by locking up. If you take off the oil filler cap when it is running you should be able to see if oil is moving in the valve cover. I would install a tempory mechanical gauge to see what the actual pressure is. If it actually has no/low pressure I would lean more towards having to much bearing clearance somewhere internally not the oil pump. If it does have real oil pressure I would remove the valve covers and inspect the rocker arms/pushrods for wear. I had a lot small blocks in the 70s and 80s that would pop a push rod through a rocker arm or a lobe on the cam worn from wear/poor quality parts (remember bad chevy cams?)
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#19 | |
Moderator
![]() Join Date: Oct 2008
Location: Wentworth, NH
Posts: 4,951
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Re: 1979 GMC 1/2 Ton No Oil Pressure
Quote:
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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#20 |
Registered User
Join Date: Nov 2015
Location: portage wi
Posts: 504
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Re: 1979 GMC 1/2 Ton No Oil Pressure
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