Hey there. I have an 85 Jimmy with pretty serious low oil pressure. The motor allegedly was rebuilt and only has 60k miles on it. I start out at about 15PSI and after warmed up it idles at about 10. Going down the road is only 15 again. I have checked the gauge. Replaced the sender. I did check voltage to the sender and its getting 6.5V. Which I'm reading the range should be between 7-9V. Could that half a voltage make a difference? I have also checked the circuit board on the cluster. I dumped Sea Foam in to hoping to clear something out. I guess the last thing to check is the oil pump but I've heard they are either working or not. Nothing in between. I am fearing the worst here. I will note that the sender has to be jetted over the clear the distributor. Could the extra fitting cause issues? Also I do have oil seeping from that fitting. Can that cause an inaccurate read? Any and all help is appreciated. And my last question is, If it is the bearings. Do I need a total rebuild? or just new cam bearings? Or whats next? How long can I drive it this way? Thanks.
CK5
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Low Oil Pressure
- Thread starter Bcwkyle
- Start date
I'd put a mechanical oil pressure gauge on it before I did anything else. Does the engine run ok? Noisy lifters or anything? If it's bearings you really do need a rebuild. "Allegedly" rebuilt already tells me you are somewhat suspicious of this claim, and you probably should be. People lie, and rattle cans are cheap.
Oh, minimum "safe" oil pressure should be 10 at idle, and 7 more psi for every 1000 rpm after that.
Well I say allegedly because it was a market place purchase. The guy seemed very trustworthy. But you never know. The motor runs fantastic. smooth and quiet.
Wont go any higher than 15 even down the highway. It had some sludge when i opened it up so I may try a new pickup screen.
Actual aftermarket gauge will tell you truth
The original motor in my 77 k10 had 120k on it, oil was at 15 psi warm
Cut the filter apart and it was flakey
When I got the cam out (going flat) the entire bottom of the front two cam bearings were gone.
But it had oil pressure!
Cut the filter apart and it was flakey
When I got the cam out (going flat) the entire bottom of the front two cam bearings were gone.
But it had oil pressure!
And NOT cheep guage from autozone / orileys / advanced in the 19.95 section in a 3 pack combo .
I'd say a $20 mechanical OP gauge would be fine. The electric gauges in these old squares are kinda bullshit often enough. I had an 81 GMC Jimmy I swapped a 6.2 diesel into. OP gauge was always in the heart attack zone. I swapped clusters, and 40+ psi at idle. Reality? Somewhere in the middle? A Mechanical gauge would have told me...but it ran fine so I just stopped looking at it.
If the pressure don’t go over 15psi with rpm I’d be really suspect of wiped bearings. I’d say trying to run a thicker oil like 10w40 or even 20w50 to see if the pressure comes up. I wouldn’t change until you do get an accurate mechanical pressure gauge value though.
Going to thicker oil is only a bandaid. It is merely confirming a suspicion that the rod/main/cam bearing clearances are way out of spec. Even moving to a “high pressure” oil pump will not fix a bearing clearance issue. Besides if you drop the pan to replace the pump you’d have the opportunity to pop a couple main and rod bearing caps and know for certain they are worn.
Going to thicker oil is only a bandaid. It is merely confirming a suspicion that the rod/main/cam bearing clearances are way out of spec. Even moving to a “high pressure” oil pump will not fix a bearing clearance issue. Besides if you drop the pan to replace the pump you’d have the opportunity to pop a couple main and rod bearing caps and know for certain they are worn.
6.2 is a 80psi guage and sender over gas 60spi stuff . So that might of been the problem if mix-n-match was going on .
Second gauge was the same 60 psi gauge so it was a direct comparison.
Mateas
Registered Member
NOT saying there isn't something wrong but my 85 305 would idle with 4 lbs pressure, running down the road was ~20. Did this the entire year I had the truck before swapping for a 383, ran fine.
Mateas
Registered Member
NOT saying there isn't something wrong but my 85 305 would idle with 4 lbs pressure, running down the road was ~20. Did this the entire year I had the truck before swapping for a 383, ran fine.
Cheap sending units give a variety of readings. Just keep swapping until you have a number you like 
(Or better yet, until the number is close to the mechanical gauge. The factory setup is far from precise.)
(Or better yet, until the number is close to the mechanical gauge. The factory setup is far from precise.)
