8.1 Oil Pressure

[Keithdee]

On my 2005 Monaco Lapalma with 8.1 engine, 26000 miles, my oil pressure cold is 40psi then drops to 21 psi when hot. Is this normal ?

[Oemtech]

Pretty much normal.

[hawkeye1995]

Yes, that is normal. I thought the same thing when I bought mine years ago. 2005 and still going strong.

[AKIQPilot]

Yep, pretty normal. Mine both run about 42psi traveling down the road at 2000rpm. They don't seem to go above about 48psi regardless of my rpm.

[akpd]

Yep normal, the 8.1 is designed to operate with high oil volume verse pressure.

[speed racer]

Yes this is the new normal. High oil pressure robs you engine of power and fuel millage. Some of the newer high performance engine use zero weight motor oil and the pressure is even lower.

[Starsekr]

Need some advice here. 2005 Winnie, 50K miles, W22 chassis with an 81L engine. Engine fried itself on a 117 deg F day while climbing a long 6% grade. 3 weeks later and $$,$$$ later I have a Jasper rebuild in it, with a new aux oil cooler and radiator and did my pre-acceptance trials. Took it on that long grade and everything was ok (oil pressure looked a little low @ 27psi) until the top of the hill when I let off the gas and the oil pressure failure alarm came on for 5 very looong seconds. (Engine 200F) Turned around, drove down carefully, checked the oil level at the bottom and it seemed ok. New Synthetic 5w-30.
This mornings oil numbers. Cold start up 44psi. Warm engine at idle 600 rpm 170F water, 21 psi. moved out of park engine to 185F, 600 rpm at a light, 17 psi. out on the road for a 5 mile drive. climbing a moderate grade, 200F, 2500 rpm ,27 psi. Stoplight, 600 rpm, 200F,12 psi. 55 mph, slight hills and valleys, 2nd gear, 4800rpm, max oil pressure of 37 psi. end of 5 miles, stoplight, 200F 600rpm, oil pressure 9 psi.
Took it back to the shop, gauge test says the 9 psi figure is valid.
Jasper says 7 PSI is the minimum acceptable pressure at a hot idle.
I am worried about crank bearing clearances.
What kind of numbers do you guys get at hot idle. I don't have numbers near as high as most of you quote while driving.

[Arch Hoagland]

Starsekr..... I can't help you on the pressure numbers, however I see you are running at 4,800 rpm.

Climbed Donner pass one time at about 4,500 rpm and the engine oil light came on a few seconds just like your's did.

Since then I never exceed 4,000 rpm. The maximum horse power and torque occur around 3,500 rpm to 3,700 rpm so that's where I keep it when going up mountains.

I also never exceed 4,000 rpm when going down mountains using the engine braking which isn't very good at keeping the speed down. I drop gears sometimes to second gear so as to not burn up the brakes.

[vettenuts]

5W30 oil has a viscosity range, with many synthetic oils being near the bottom of the range. Some are very close to the upper 20W range. Based on your numbers, I would try an oil that falls in the upper end of the 30W range if you want to stay within the owners manual.

Personally, and I know it is not recommended in the owners manual, I would go to a 40W oil that falls at the bottom of the 40W range. The Mobil-1 European 0W40 FS barely makes it into the 40W viscosity range.

[Oemtech]

I ran dang evrey major brand in my 8.1l and had it tested. The best Penz or Castro 10-30.

Got living daylights scared out of when I switched to synthetic. My copper levels went thru the roof. Switched back to Dino oil and all was well again. It took me some time to get to thebottom of this mystery. I found a tech bulletin from Caterpillar that indicated that the copper would go high on switch to synthetic due to the way they solder the fittings in the oil cooler. Bottom line it takes 2 to 3 oil changes before the copper levels drop to the normal range.

[Starsekr]

Thanks for your advice. Vettenuts and Dale. (Dale used your pages a lot, thanks for that too. Arch, the 4800 was on a mostly flat in 2nd gear to see what the max driving pressure was, the light came on climbing Union Pass out of Laughlin, about 3500 rpm, 3rd gear, 50 mph.

[Starsekr]

Shop changed the oil from 100% synthetic to a blend. No change in observed pressures. Idle is still 7-9 psi hot, 25 psi at 2000 rpm in cruise, 37psi maxed at 4400 rpm coming down a 6% grade.
Guess I'm going to run with what I got. tnx all.

[vettenuts]

One other thought. Not sure how you are measuring the oil pressure, but wondering if it would be worth verifying you observed pressures with a mechanical gauge.

[akpd]

It sure sounds like a bearing clearance issue by the way the pressure drops when hot, cam or main bearings maybe?