high oil pressure reading
 

I just acquired a real nice 1985 Silverado. It supposedly has crate 350. The oil pressure gauge pegs over to 60 lbs. when I first start it. It stays there several minutes then settles in at about 35. Any ideas on what might be causing this? My first thought was a faulty gauge but i've never had one act this way. Also how can I identify this engine as a crate. THANKS.

Thanks. The first thing I did was replace the oil. Nothing changed on the gauge. I'm thinking the gauge is bad or perhaps a stuck spring on the oil pump. The engine runs fine and doesn't smoke. I got it cheap enough to not care if the engine is a crate or not. The build tag shows it had a 305 originally. It has the GM Goodwrench 350 valve covers but that doesn't mean anything. I'll check the stamping number with the site you gave me.

I have the same problem in my 1970.

I've changed the oil as well..........

Remains unchanged...............

Maybe the pressure sender is for a different gauge. It's happened to me @ work before. (I'm a parts store counter rep) I don't know if there are different sender options in this case though.

What kind of gauge are you using, stock?
I would also check the sending unit.
What is your idle speed when the pressure is up?
Is it possible that your choke is making it idle faster, which also would cause your oil pressure to increase?
I know that the first start of the day is always the highest oil pressure (at idle) on my truck.
What oil are you using?

Get your truck on the freeway, get it up to 70-75 for 8 miles or so. Get off the freeway and stop at a light. What does your pressure read now? Go up the block, regular street speeds and stop at the next light, whats your pressure now?

Mine does that in my 78 pickup it goes up to 60 then dropos to half way but when i sit at the light the guage goes up and down kind goes low then the middle and keeps doing this i have changed the oil and still the same it never used to do that when i first got the truck it just started. any ideas?

My 85 silverado does the same thing,but made sure by hooking a guage directly to the motor.and it read good,asked a friend about it that worked for gm for 15 yrs and he sait they were always having problems with the guages in them,was usually printed circuit cause they were crap he said.there are 2 clips that go into the back on the printed circuit,sometimes the clips don't contact the printed circuit and the guage is then inacurate.you can also convert this guage to the mechanical one on the 75 chevys and run the tubing through the firewall and thread the fitting into the block,then you know your oil pressure all the time.After i checked with a propper guage,i just got used to my chevy having next to nothing or no oil pressure.:D :bowtie: :canada:

Typical Gremlins!

hey mike'76, think it's possible they may have put a high volum oil pump in before sticking it in the truck? the reason i say that is I had a melling hv pump in my motor and it read about the same way. when cold it read ~60 then held ~30 to 35 when warm at idle, but out on the highway it would go back up with the rpms. does the pressure increase with the rpms on yours?

This is the stock gauge. It startes out at 60 then after several minutes drops to 30-35. It usually stays pretty close to that. It has, on occasion rev'ed back up close to 60. When it does this it goes up and down with the RPM'S. I'm going to hook up a mechanical gauge just to find out for sure. All of my years dealing with small blocks I worried about worn out motors with low pressure. I'll let you know the outcome of this mystery. It will be about 10 days or so before I can do it. They are doing another surgery on my back on Monday (the third one). Thanks for all the replys.

Mine goes up when im driving then when i stop at a light it drops. i have the sending unti the sit behind the dist and theres a big one back there with a small one in the top of it. i think its shot. looks old.lol any suggestions.

My '02 Camaro has a cold start oil pressure of 60psi until it warms up. At full op temp it drops to 40 psi. This is with 5W-30. It was the same way with my '98 Camaro as well. I know the '98-up Camaro has a high volume pump from the factory. Maybe your crate engine has a HV pump as well?

My trucks oil pressure has done what your oil pressure is doing. I had it rebuilt about 2 years ago. I believe they may have put a high volume oil pump in. High volume pumps are okay, but you want to stay away from high pressure oil pumps. Sounds okay to me with a reading of 60 psi then 35-40 warm @ 800 in drive - near 60 psi with revving while warm - over 60 cold.

I installed an aftermarket oil pressure gauge (sun pro), works pretty good but I would advise against using the plastic line they give you in the package. Copper line is the better way to go. If you ever want an oil pool in your floorboard just have that plastic line break and let the fun start. That is the quickest oil change I have ever seen in my life :eek:

The biggest problem with the plastic line they supply is that brass compression rings are used with them and that's a no no. Brass compression rings and plastic line don't mix without a fight and the brass always wins. It always seems to be at the guage too ;)

I've had alot more trouble with the copper line kits than with the plastic ones. With my VDO gauge, I purchased the copper line because I figured it would be better.. well after trying to fix the leaks at the gauge head, I finally installed the plastic line instead. Works great now, not a leak.

And no more 'delayed' oil pressure readings.

Jeff :burnout:

I say if you get a mech gauge get a steel braided line from Autometer. Its a very quality line and it hasnt leaked once on me. They are pricey, but very good quality. The plastic line busted within a few months. I looked down and thought who the f*ck spilled soda in my truck. Then I found it was oil, boy was I mad. Talk about sh*tty, driving home with a cup catching the oil is a nightmare, even more so when you have to drive a manual :)

I have a stock 350 crate, its about 4 years old and it still runs great. I use 20w-50 in it now. It does alot better in the heat. After freeway driving it doesnt drop lower then 20, usually its 25 after high speed driving. Around town it never goes below 30. In the morning its arounf 45-50. Its a autometer mech oil pressure gauge and it looks like a tach when your driving. Its pretty cool :). Anyway at about 4k rpm its around 60. At around 4500 rpm the pressure is getting closer to 70. Normal operating pressure is anywhere from 30-50 depending on the engine speed.
Hope that helps some.

I may be wrong, but I'd think the 20W-50 oil would cause the higher pressure due to the thicker viscosity.

I can tell a slight difference in my car between 5W-30 and 10W-30 although it may be due to the extremely close tolerances of the GENIII SBC. For instance in the summer months running 10W30 keeps my oil pressure a hair or two above 40psi at idle. Using 5W-30 under the same conditions drops the pressure to just below 40psi. These observations have been at normal op temps.

I jut mentioned that, because I was mentioning my readings. Thought it may help out :) Kinda of crucial when talking about readings.
I used to use 10w-30 -40 but I would get pressure drops after high speeds. Went to 20w-50 and everything stays nice and in range.

Hey i was wondering where could you hook up a mechanical gauge and still have the one in the dash still working. i want to hook one up to compare it. Meaniong where on the engine.

Thanks

Back of the block behind the dist. There is a brass fitting tapped into the block where the sending unit is. You'll have to use a splitter of some sort to plumb a mech. guage.

Whatever works. It sounds like an oil starvation issue though.