Thick oil causing low oil pressure?

[drice72]

I have an oil leak in my 1993 C1500 4.3. The leak is coming from my intake, and I plan on putting in a new gasket kit this weekend.
This thing is leaking a quart a day, so I got the bright idea to put in some 10w-40 to maybe slow the leak.
I think this was a huge mistake. My motor now won't make enough oil pressure to maintain speed on the interstate.
I go along fine for 12-20 miles then it starts to lose power, valves tick and it feels like I'm losing compression.
I can let the truck rest and it will drive fine. Also if I'm not trying to push it really fast it will do fine. Just driving on the interstate going to work.

Would that weight of oil cause this, or do I have bigger problems than the intake oil leak.

 

[98_k1500]

You sure you have not run it low of oil? If so you probably need a motor. (by low i mean 4-5 qts?)

 

[drice72]

No, I have been checking it everyday. the most I have had to add is two quarts.
It didn't start doing this until I added the 10w-40, that is why I suspect it is too heavy.

 

[someotherguy]

Even a well-used engine still in good shape should be just fine with 10W40. During the long hot stretches here in SE TX I've used straight 40W plenty of times and never had problems with oil pressure. Sure, it's best in general to stick to what GM says is correct for your engine, but the 10W40 won't be your oil pressure problem.

If you think it's the issue you might as well change back to the correct grade of oil. That 10W40 isn't going to slow any leak down.

Richard

 

[drice72]

I think I'm going to do that.
It's just weird, it doesn't smoke at all, never has burned any oil, just external leaks here and there.
This last leak is a big one, it pours out from under the intake and that is the only leak on the motor.
I have removed the inspection cover to make sure there is not a leak around the rear main.
In side of the cover was just dirty, no oil.

I only lose power after driving for awhile. Even after that I can drive at lower speeds, just not on the interstate.
I have a lot of valve chatter that doesn't happen until I start losing power either.

It won't keep over 20lbs no matter how fast the motor turns. When I first start, I get normal pressure.

 

[michael hurd]

Sounds like all the oil is being pumped up to the heads, and taking it's sweet time to drain back through the likely half plugged oil return holes in the cylinder heads and the pump is starving for oil. High RPM + thick oil + slow draining back to the pan can certainly cause this.

 

[joedee]

Sounds like all the oil is being pumped up to the heads, and taking it's sweet time to drain back through the likely half plugged oil return holes in the cylinder heads and the pump is starving for oil. High RPM + thick oil + slow draining back to the pan can certainly cause this.

I run 50 weight racing oil spring through summer no issues cold start 55 to 60 lbs pressure hot 45 at idle 50 t0 60 at highway speeds . 5.7liter with 194,### miles . You may want to at the least flush out the motor with something . Maybe invest in a new oil pump as a second to last option last option is rebuild the motor ..

 

[drice72]

What do you recommend to use to flush it?
I was planning on running some Seafoam through it, is there anything else?

 

[MXR597]

I may catch some heat for this but I run 15w-40 in mine and I have never had a problem with oil pressure.

 

[98_k1500]

I run 15w40 rotella in everything i own. Always have, never had a problem. Its pretty hot down here too tho. As far as engine cleaning goes, Iv never seen anything that works better than a cheap quart of trans fluid in the oil a couple hundred miles before a change for a few changes. +1 on the sludged up engine theroy if its full of oil. If you want it clean, you can pull the oil pan and intake off, chisel all the crud off the valley (thats where its gonna be accumulated) flush it all out, and seal it back up. Sounds like this will be your best option anyway if it needs intake gaskets anyway. If you don't pull the oil pan, I would NOT suggest cleaning the lifter valley. That crud that you miss WILL end up in your oil pump.