I posted this in the 302 forum but they told me to ask here too. I finally went out and bought a real oil pressure gauge for my truck to actually see what kind of pressure I have. I bought a gauge that has an electrical sender but I did confirm this with a mechanical gauge as well. At start-up the truck has around 50-55 psi. After the oil and engine warms up it has about 10 at idle and 25 at 2000 rpm. After that the gauge does not really move any higher whenever I rev to 3000 rpm or so. I am using 10w30 right now because winter is coming and it has started to cool off around here. I was using 10w40 during the summer but I did not check the pressure until now. I don't think that the motor is knocking or anything, but I think that I do hear a noisy lifter or two when everything first starts up after a long sit, like overnight. This usually goes away after everything warms up. Any ideas? I was thinking the pump is going bad or something is blocking the pickup tube. I hope that it is not the bearings. Any thoughts are greatly appreciated. Thanks guys.

 

Not sure I can answer that question as I do not have a real gauge, sorry. I have an 86 302 I can here some lifter noise at start up, pretty sure that is normal.

Anyway, I am thinking about installing an electric gauge as well, how did you do it and was it difficult? I would like to keep my stock gauge working as well.

Maybe someone can correct this but I think your pressure should rise about 10psi for every 1000 rpm.

 

I got an extra 8 psi at 2000 going from 5w30 to 10w40. You could run a 5w40 synth in the winter. A likely culprit is a partly clogged pickup screen. To rule out the lower end bearings try this test, run on the freeway with it under load for 20 seconds (higher gear and uphill helps). Then quickly let off the gas pedal (leaving it in gear). If the psi jumps up more than a couple psi it suggests loose bearings in the low end. Loose rod big end bearings will cause a lowering of pressure with rpm as centrifigual force keeps throwing off more oil. Could be a worn pump or a weak spring on the pump pressure relief valve (and that is what I think my problem is, but not so bad as I get 35 psi on 30 wt.) If you replace the pump IMO it is best to go with a stock pump as high volume can take too much up top faster than it can drain back and sometimes cause dry running. My pressure maxes about at 2000 or so: The relief valve will limit that (WO the relief valve it would keep going up until if you reved it enough you might blow the filter).

 

How many miles on engine? A general rule of thumb is you need 10psi for each 1000 rpm. So you should be ok unless you tow heavy loads and lug the engine. The 5w40 synthetic may work well.

 

The truck has just under 100k miles on it. The motor runs good though, a little hard starting at times but that is another issue. As for the oil pump, do you really think that the pressure will not rise any more past 2000 rpm? So what about this 10 psi for every 1000 rpm or does this just constitute for up to 2000? The only problem that I have with running a 5w40 synthetic is that I have to keep using a synthetic afterwards. The truck does not burn oil at all but does have a couple of small leaks, front and rear seal, both still on the list of things to do. I may consider the synthetic though. So TallPaul, if there is not really a spot that I can run that long uphill to test to see if it is the pump, would the test still be as accurate? Thanks again guys for all your help.

P.S. -- rgillies1986, putting in a real gauge is pretty easy. Any type of gauge that you get, whether electronic sender or mechanical will have instructions with them. It is really self explanatory. If you go with a mechanical one the only thing that I would watch for is do not over-tighten the compression fittings at the block and on the gauge. That can cause leaks.

 

Just for clarification here is a direct quote form a post at another forum from which I drew some of my above discussion:


"The way to tell if the bottom end needs rebuilt is to:
Get an accurate mechanical OP guage.
Then run the engine full throttle for 20sec (at highway speeds)then let completely off and watch the guage. When you let off the crank will center its self in the main bearing because there is no longer a down load on the crank. When the crank is centered, less pressure escapes from around the main bearing. If the OP increases more than about 2-3 psi then the main bearings are getting loose.
I have personally seen this and have pulled the pan and found worn mains, replaced them and the change in OP went away. Its been my experience that rod bearings wear slower on my V8s and are not a major source of lost OP(may not be the case on a long stroke straight 6). Cam bearings can also cause low OP."

 

You do not need to stay with synthetic, you can switch back and forth. Synthetic may cause the leaks to worsen due to the extra cleaning power. 10 psi per 100 rpm is for an engine loaded. so yes 4000 rpm sustained shoud have 40psi. ocasional runs up the tach during acceleration should not be a problem if you can maintain around 30psi.

 

you need a heavy oil not 10w30 try rotella 15w40 it is good oil

 

The 15w40 is good for summer, but in winter I would drop down to at least a 10w40 in IL as it gets pretty cold there, probably a lot of below zero F mornings.

 

I would run the 5w40 synthetic for piece of mind. It will flow plenty fast and provide enough film strength. This is the oil recomended for diesels that have up to 20 to 1 compression. Only side effect will be the extra cleaning power of the strong additive pack that may cause existing leaks to be worse.