The Stovebolt Site Forums The Shop Area Engine Shop Oil pressure question

I have a 235 (58-61) in my 49 chevy pickup. When i start it up i show about 25 on my gauge. When i start driving and it gets good an warm it looks (on my gauge) like i go down to around 5 pounds. Gauge also seems to fluctuate up and down running through the gears. Do i have anything to worry about here? this is not a new or rebuilt engine, runs good and quiet, start good. Any advice would be appreciated. Thanks.

Sounds normal to me. My 248 tops 60 psi when cold and drops to under 15 at warm idle.

Not normal for the 235. Should do much better that 25psi cold. The 235 that was in my truck even worn when just about peg the 60lb gauge when started cold. Once hot it would drop to around 10psi at idle. My 261 would do better than that.

Most 235's I see run at least 30 psi warm and idle at 15 psi.

If your warmed-up 235 engine at idle goes below 15psi, the most likely explanations might be thin oil or bearing-wear.

Im running 10W30 now do i need to go to a thicker oil? Trying to keep from rebuilding the engine (no Money) what oil would u suggest, live in Tennessee, so no real extreme weather conditions. Thanks.

I like to run 15W-40. That should give you a little pressure boost due to the low-end viscosity being a little thicker. Another option would be 20W-50. On a really worn engine, I've run straight 30 or even straight 50 weight racing oil, but do a good warmup before driving in cold weather if you go with oil that thick.
Jerry

I use (or, have used) all the oils described by Jerry, above (for the reasons Jerry nicely describes above).

Several years ago, my Suburban's 235 engine starting showing lower and lower oil pressure, until it was reading 0 psi at running temperature at idle (w/20W-50 oil). I took it out and put it to rest (and temporarily put in a spare 261 that I had). I did not want to throw a rod or hurt my 235 - I will rebuild it and put back in someday (with a later 848 head, a 261 cam, and a slightly larger carburetor).

Put in thicker oil and drive the engine. When the oil pressure gets dangerously low at idle, or when/if you hear an engine/rod knock, retire the engine.

Had a 56 Chevy two door that smoked real bad. When I pulled into a gas station, the put in 90 WT gear oil in it for me. They would ask me twice if I said 90 wt. They would fill up a container from a oil pump that had a bell on it to indicate quarts I guess. In Arizona it stayed low enough viscosity. It still smoked. Pressure was real good though

Drop the pan and plasti-gauge the main bearings. If worn 3 thou or better time to replace the bearing. If compression is good, I wouldn't touch the top end.

90% of wear is at start up... so using super weight oil to get the oil pressure up is really hurting at start up when the oil is to thick to make a proper fluid bearing.

I use a 20/50 and my 216 gets up to 30 on start, 14-15 warm and around 10 or so at idle.