97 chevy 1500 oil pressure at 55 with check gauges light on

[bbullsj]

i have a 97 chevy 1500 cheyenne truck. the engien has 168,000 on it and i'm pretty sure it's never had anything done to it. the oil pressure has been down to 10 before b/c i have oil leaks and it was low on oil. usually it runs about 18-24. lately with the colder weather it will jump up to 50-55 and if i don't let it warm up for about 5 minutes before i leave in the morning the check gauges light will flash a bunch and has stayed on a couple times. once the truck it warmed up pressure is at it's normal 20 or so. i have had this truck for 5 years and have not had this problem before. did an oil and filter change b/c it was due but didn't change anything. what should i be looking at for a cause? i know low oil or worn rod bearings can cause low oil pressure but not what would cause high pressure when cold and then be normal when warm. i would really appreciate any help.

[jdmccright]

There are basically two things happening together to explain it. First, the difference in viscosity when the oil is cold versus hot. Any oil's viscosity will drop as temperature increases. Single viscosity oils like SAE 30 for your lawn mower will thin out as they heat up during use. However, motor oil is a "multi-viscosity" lubricant. The "weight" that it is labeled, 10W-30 for example, conveys the oil's relative viscosity when cold (the 10) and hot (the 30) when compared to a single viscosity oil of that weight. You can google for more on the subject...there's nice graphs that show how viscosity changes much better than I can describe. In summary, the oil will thin out as temperature rises but not as much as a single viscosity oil will.

Taking us back to you, when the oil is cold, it is more viscous and thus harder to pump through your engine, resulting in a higher oil pressure. But as the oil's temperature increases, it thins out and flows easier, reducing the system pressure.

Now, since your engine is well seasoned, you'll have some significant wear in areas that have to contain the oil. When the engine is cold, everything contracts and reduces those gaps and helps keep pressures higher. But as the engine warms up, everything expands slightly and allows oil to seep out from those gaps, reducing oil pressure.

Hope this helps!

[777stickman]

My '98 service manual says the "check gauges" light will come on for either high coolant temp or low oil pressure.

Minimum oil pressures are: 6psi @ 1000, 18 psi @ 2000 & 24 psi @ 4000.

1st thing I would do is install a manual oil press gauge and compare it to the dash gauge.

Let us know.

[j cAT]

with 10-30wt oil and cold engine start in cold weather oil pressure will be at 70-80psi for a time, until engine warms up..this is normal ..

when the engine is at normal temp with 10-30wt oil pressure should be 40-55psi. this is with a good engine ,,, not worn excessively..

most times a worn high mileage engine needs a good oil change..

cold , sludged oil will muck up the sensors...causing your light issues.


using about 5oz of marvel mystery oil to the engine oil, run for only a few hundred miles ,,,,then with the engine at the normal operating temp drain all this hot oil out...this should remove all of the goop in the crankcase ..allow 30 minutes to drain...

use a good wix or purolator plus oil filter, no frams ...

with your engine you may want to do this prior to your scheduled oil changes to help prolong what life is left to this engine....

[bbullsj]

oil viscosity has absolutley nothing to do with it. i know what it is and that doesn't help me. what i'm looking for help is, why would all of a sudden after 5 years of owning the truck, it start acting up and having really high oil pressure.

i don't have a pressure gauge and it's getting very cold out so i'm not as inclined to check it and compare it to the dash gauge :S unfortunatley i'm sure i'm going to have to do it sometime here soon.

where can i get that marvel mystery oil? any auto parts store or somewhere specific?

[ctwright]

I agree with the person who said to get a manual gauge and compare the pressure, it could just be your oil pressure sending unit needs replacing

[bbullsj]

where can i get an oil pressure gauge and where is the sensor located at?

[ctwright]

I believe it's above your oil filter, check advance or autozone for the gauge

[j cAT]

Originally Posted by bbullsj

oil viscosity has absolutley nothing to do with it. i know what it is and that doesn't help me. what i'm looking for help is, why would all of a sudden after 5 years of owning the truck, it start acting up and having really high oil pressure.

i don't have a pressure gauge and it's getting very cold out so i'm not as inclined to check it and compare it to the dash gauge :S unfortunatley i'm sure i'm going to have to do it sometime here soon.

where can i get that marvel mystery oil? any auto parts store or somewhere specific?

the check guages light comes on when one of you guages is out of the normal range. fuel supply,battery volts,oil pressure too LOW,engine temp too high . so what guages do you have ? are they all in the normal range ?

the engine codes should be pulled if any .


advance auto / auto zone , and many other auto stores carry marvel mystery oil. this product has been around for many decades .

sometimes on these old vehicles the ground wires / frame ground connections need cleaning..could be bad ground causing this.

[bbullsj]

i have batt, fuel, oil pressure, and engine temp. fuel and batt are fine. oil pressure has been reading high since the cold weather started but is normal when the engine warms up to normal operating temp. coolant temp doesn't get above 160 but blows nice hot heat. i figured the thermostat was stuck slightly open and have been going to replace it but have not had the time. the check engine light does come on and go off and is an o2 sensor code (i don't remember the code number).

i will probably get some of that oil and put it in and see if that helps. not right not but sometime soon here. i just did an oil change on it and feel bad about running 500 miles on brand new oil. i have always used a synthetic oil. would it have anything to do with that coming back to bite me?
where would i find the ground wires at and how many are there?

[bbullsj]

well i would love to say i got it all fixed and the truck runs fine now but thats not the case. i wrecked the truck and am waiting to find out if they are going to total it or not. if they don't total it i will be trying to fix the problem still.

[tblake]

Oh no, sorry to hear that!

Was it in that big wave of or snow that hit last friday/saturday? I know in MN we got blizzard conditions. 8-10 inches in my area and 20+ down in southern mn. Coupled with high winds, drifts as high as my waiste.

[bbullsj]

no it was dry roads just rush hour traffic and a guy slammed on his brakes in front of me. the truck is totalled so it won't get fixed til next spring and will get a new engine then too.