My opinion is using a thicker oil like that will prematurely wear out the oil pump over time . If it's over 80lbs now at cold idle thats more than the engine needs when warm at wide open throttle . My last race motor made 31 lbs at over 8k rpm with 40wt and lived a long life .No idle though cause pressure was near zero .quote:
Originally posted by bugman53:
In my 1994 Grand Cherokee(5.2moparV8)i switched form castrol Gtx 10-30 to Mobil delvac 15-40. the motor has 150K on it. With castrol it has about 35psi at hot idel(600rpm) and 65psi cold ideal but now with Mobil it has over 80psi cold and 45psi hot idel the cold pressure seems really high to me and will that cause any damage. Like oil starvation due to less flow?but it consumes almost no oil.
What is the hot oil pressure with each of these oils? The critical number usually hot (and I mean after a good 15 mile run) at highway speed, maybe around 2000 or 2500 rpm. You service manual can tell you the spec. For example, my pickup ('95 F150 300 I6) specs 40-60 psi hot at 2000 rpm. I was getting 35 with 5w30 and now am happy running 10w40 and getting 45 psi. In your case, given the idle pressure, I strongly suspect that you should stick with a 10w30 (presuming the gauge is good). If in doubt about the gauge the shop can hook up a precision test gauge, but again it has to be hot. You will know when it is hot as the pressure will slowly come down from the cold pressure as you drive and then will stabilize after 10 to 15 miles. But 80 cold is not necessarily too high as my motorhome runs 75 cold and then around 58 hot at 2000 rpm. Get the spec pressure and check the 15w40, you may be OK, but if too high, I would drop back to 10w30. Why did you stop using 10w30, using oil? Are you burning it? Maybe a different 10w30 will result in less consumption.quote:
Originally posted by bugman53:
In my 1994 Grand Cherokee(5.2moparV8)i switched form castrol Gtx 10-30 to Mobil delvac 15-40. the motor has 150K on it. With castrol it has about 35psi at hot idel(600rpm) and 65psi cold ideal but now with Mobil it has over 80psi cold and 45psi hot idel the cold pressure seems really high to me and will that cause any damage. Like oil starvation due to less flow?but it consumes almost no oil.
Excellent point. When I ran 5w30 in my pickup and then switched to 10w40 the cold pressure was the same for both, but the hot pressures changed. The oil pump pressure relief valve is the limiting factor, unless the thinner oil just could not get enough pressure to open the pump relief valve; then you would see a difference. He needs to look not only at the hot cruise speed pressure, but also find out what the pump (not filter) relief valve pressure is supposed to be.
Keywords.. YOUR OPINIONquote:
Originally posted by Motorbike:
My opinion is using a thicker oil like that will prematurely wear out the oil pump over time . If it's over 80lbs now at cold idle thats more than the engine needs when warm at wide open throttle . My last race motor made 31 lbs at over 8k rpm with 40wt and lived a long life .No idle though cause pressure was near zero .quote:
Originally posted by bugman53:
In my 1994 Grand Cherokee(5.2moparV8)i switched form castrol Gtx 10-30 to Mobil delvac 15-40. the motor has 150K on it. With castrol it has about 35psi at hot idel(600rpm) and 65psi cold ideal but now with Mobil it has over 80psi cold and 45psi hot idel the cold pressure seems really high to me and will that cause any damage. Like oil starvation due to less flow?but it consumes almost no oil.
There is alot to viscosity choices and hydraulic lifters as well . The makers made choices for the owners since many don't fully understand the effects . For more info search Rhoades Lifters . They are a hi bleed lifter very tempermental to vi .
If your having consumption problems I would suggest one of the better HM oils available in a 10w-30 wt . Castrol and Pennzoil are but two of these type products that are actually designed for higher mile engines like yours .
I really think you will benefit more from a hi-mileage oil than that diesel oil your using now . But you will have to try it and decide for yourself . A little more money than a tractor oil but hey , what did that last tank of gas cost ya ?
Actually, Rand, you're statement isn't exactly true.quote:
Originally posted by Rand:
Keywords.. YOUR OPINION
I think you are reading to much into this. 15w40 is not any thicker than 10w40 when hot... its not some magical goop you run only in diesel engines..... Its just OIL.
Rand
