Oil pressure changes

[Machineria]

I've had this truck for two years. One of the first things I did was to hook up a mechanical oilpressure gauge; the factory one was kaput and I like units on my gauges, not just L and H, thank you very much. Cold idle about 85psi, cold revs over 100, warm idle 25-30, cruising around 40-60. But in the last six months or so, pressure has been a little lower: 75-80 cold idle, as low as 10 warm idle. Is there a good reason this might've happened, or do I have a failing oil pump, or just a crappy Sunco gauge?

[Machineria]

Forgot to mention (and can't edit the post for some reason) that the previous owner, known to be a clueless idiot and suspected to be a liar as well, claimed to have the engine rebuilt not long ago. It starts very easily regardless of temperature, so I think the compression is good, but has been burning oil since I've had it.

[camoit]

How many miles are on the oil? Change it every 4000 mile unless it's synthetic then you can run longer.

[wrngwae]

the balance shaft bearing are a guaranteed failure. its a big unbalanced slug turning 2x RPM. those bearings are the first to go and can greatly affect oil pressure. i would suggest you pull the timing cover and either eliminate them or have new bearings installed... just a guess.

[recian]

How many miles on the truck? The diesels are hard on the rings and head gaskets (not your problem) but over 300psi of compression pushing that piston down does alot more to the rings and bearings than the 175 you find on the gas engines. Look at the valvetrain through the oil cap, look up the oil drain hole at the bottom end if you can see it. Look down the timing cover area. There's always signs of engine work even if it wasn't cleaned. He may have had the typical head gasket failure and warped the head and redid the head and called it a rebuild. A new top end will put more stress on the bottom end. Burning oil is either rings or valve seals. Low PSI is either pump or bearings. It's not common to see low PSI and oil burning together unless oil pressure is very low to the point it could have damaged the engine. Also good compression doesn't always eliminate oil burning at the rings. Happens to higher mileage hondas all the time. The compression and oil rings are separate. The oil rings will fill with carbon or sludge up with oil while the compression rings rely on cylinder sealing. Sealing is one thing but the ability to hold oil is another.

[Machineria]

Unknown miles on the engine. Could be 10k, could be 300k. Valve stem seals were replaced recently and didn't affect oil consumption one bit. Oil has not been changed regularly, but has been topped off (due to burning and leaking) about as much as it would've been changed. The latter situation is getting remedied soon.

I'm scheming up an overhaul for this poor engine. Rings, gaskets, balanceshaft bearings (will look into the consequences of disabling them altogether), and then I can run synthetic oil. Can I run lightweight stuff, like 5W40? I've been using non-synth 15W40 for now.

[camoit]

I would run Dello 400GL not the Dello 400LE. The LE is for light emission engines with a cat and exhaust injectors. Stay away from automotive oil in the engine. It brakes down faster from the diesel.

[Machineria]

By "automotive oil", do you mean gasoline (API S-rated) as opposed to diesel (API C-rated)?

[camoit]

yep. I use Dello 400 GL (chevron) in all my cars, except my build truck. It's on brake in oil now. Then I'll probably use some kind of race oil. Who knows at this point.

[Machineria]

When the finance committee for this truck gets around to approving it, I'll rebuild the turbo or piston rings or both, replace all the oil seals, and run nice synthetic oil in it. But for now, I've been using various cheaper brands (mainly because it leaks and burns so much) of 15W40 CF-rated oil.