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Re: Oil pressure drops to almost nothing at idle when hot [Re: frscke1] #751393
August 07th 2019 4:26 pm
August 07th 2019 4:26 pm
Joined: Jul 2019
Posts: 38
Ohio
M
Mikeburkey Offline OP
newbie
Mikeburkey  Offline OP
newbie
M
Joined: Jul 2019
Posts: 38
Ohio
How would I go about finding if or where there is a clog?


Chevy Van G20 3/4 Ton 5.7 L 8 Cyl
Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751422
August 08th 2019 9:44 am
August 08th 2019 9:44 am
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
Just4fun1991 Offline
member
Just4fun1991  Offline
member
Joined: Feb 2018
Posts: 140
Cedar Rapids, Iowa
It sounds like you have owned the van for about 1,000 miles. Just a few questions for you.

It sounds as if when the engine heats up, the oil is breaking down thus the oil pressure is dropping.

When you changed the oil, did you change from a conventional oil to synthetic oil or vise versa? Sometime this can cause deposits to break free and cause issues (going from syn to trad oil)

Did you use the correct oil weight per owners manual?


What you don't know (as not to many previous owner's will tell you is they over heated the engine or ran it low on oil once and thus scored the bearings)
What you also don't know was how far was the van driven with low to no oil pressure from the prior owner.

Since you have owned it about 1,000 miles has the van used any or much oil during those miles?

In the past, you could do to a Caterpillar dealer and get a sample vile, and then drain your oil and take them a sample and they would analyse it for you for a fee and can tell in most cases if you have bearing issues or what by the oil.

Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751426
August 08th 2019 12:05 pm
August 08th 2019 12:05 pm
Joined: Sep 2005
Posts: 8,828
Georgia, USA
CatFish Offline
carpal tunnel
CatFish  Offline
carpal tunnel
Joined: Sep 2005
Posts: 8,828
Georgia, USA
Gee guys.
I've owned lots of factory stock 350 Chevys. Cars and vans. 8 pounds on the factory gauge at hot idle sounds about right. I've had 'em show that on the factory gauge and still drove 'em for over 100K miles with the pressure dropping at every idle.
Our GMC now has over 335K miles. When it was a about 295K it had a small oil leak that required removing the pan. While I was in there (because of the ease) I replaced the oil pump with a high-volume pump (and the required new larger pickup assembly). BTW, it was clean as a pin inside the pan. After there's no difference when she's warmed up, still about the last notch on the factory gauge at idle, 40K miles later.
Runs about 30 to 35 psi warm on the road. Never any noise. 5w30 or 10w30, full synthetic or not, Pennzoil, Quaker State, or Bell-Ray. I do run a zinc additive about every other change and a K&N filter. The filter is just because it's easier to get on and off.
Our '95 G20 has the factory oil cooler and only 60K miles. It shows a little higher at idle but not much.


"The best break anybody ever gets is in bein' alive in the first place."

Porky Pine
Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751428
August 08th 2019 1:53 pm
August 08th 2019 1:53 pm
Joined: Jul 2019
Posts: 38
Ohio
M
Mikeburkey Offline OP
newbie
Mikeburkey  Offline OP
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Joined: Jul 2019
Posts: 38
Ohio
I went from conventional to synthetic I'm pretty sure, to be honest I have no idea what the previous oil was, the van was my great uncles and he passed away and I bought the van at the point. I put the correct weight oil in 5w30 as that's what it said on the oil dip stick cap. But to be honest it could be something as small as a low idle setting, I'm looking to install a tachometer to check that and so I can monitor the engine as well. And to add on its only at idle, when driving its about 40-50 psi depending on what road and speed etc but I don't think it's too big of a problem, I'm going to top off the oil because I'm sure since I changed the oil it has burned some off. I have had the van for about 700 miles, I got it at ~85,500 and it's now at ~86,200.

Last edited by Mikeburkey; August 08th 2019 1:56 pm.

Chevy Van G20 3/4 Ton 5.7 L 8 Cyl
Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751438
August 08th 2019 3:38 pm
August 08th 2019 3:38 pm
Joined: Jun 2010
Posts: 14,440
Van Diego California
frscke1 Offline
frscke1  Offline

Joined: Jun 2010
Posts: 14,440
Van Diego California
Thats the thinnest oil there is ... try thickening up your oil ... you may be passing it thru your valve guides or rings.

When I change my oil (Mobil 1) my motor takes 8 qts ... 5 str 30w and 3 str 40 w. I run 2 qt Car Quest oil filters.


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'93 CHEVY G30 454 4X4 SPORTVAN EXT 146" WB
'92 CHEVY G30 454 BEAUVILLE EXT 146" WB
Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751514
August 11th 2019 12:10 am
August 11th 2019 12:10 am
Joined: Apr 2010
Posts: 2,685
San Diego
W
wrcsixeight Offline
veteran
wrcsixeight  Offline
veteran
W
Joined: Apr 2010
Posts: 2,685
San Diego
Technically, 0w-16, is the thinnest oil currently available on store shelves.

Some 5w-30 will actually be thicker than a 10w-30 at 100c degrees or at
Hths viscosity. High temp high shear, is representative of what is occuring in the bearings.
Again some 5w-30 can have higher hths viscosity than a 10w-30. Not all. The allowances vary fairly widely.

Oil level will have little to do with oil pressure, until it falls so low the available oil gets significantly hotter,thus thinner, or when it drops so low the pick up tube for oil pump starts sucking air.

In 2007, my oem op gauge was reading alarmingly low at hot idle. I installed a mechanical gauge, which revealed excellent oil pressure hot at idle.

If the engine does not start ticking or clacking at hot idle the op gauge is suspect number one.

If it is making noise hot idle, does the dipstick smell like gasoline?

Excessive fuel dilution thins oil, reduces oil pressure.

Actual low oil pressure at hot idle can be helped.with thicker oils 15w 40 or 20w-50. The 5x-xx and 0w-xx oils do lube better in cold weather with cold engine, but offer no benefits in warmer environment on older engines.

Dirty sludged engines might quickly clog oil filter, which might cause low oil pressure reading if the filter's internall bypass is not functioning correctly.

There is tons of bad info regarding motor.oil repeated over and over as verbatim on the internet and many self proclaimed experts are quite delusional.

I installed a mechanical gauge as it was cheaper than a one time test gauge.

If your engine is still smooth and quiet at hot idle, suspect the gauge first.

Step up oil thickness if it is noisy and know this solution might be short term.

Thickeners like .lucas 'oil stabilizer' have no detergents dispersives antiwear extreme.pressure friction modifying additives. LoS will duliluted those additives in a properly formulated motor oil.

LOS might also render the anti foaming additives in a properly formulated motor oil useless ,and the oil pump will then send frothy oil through the bearings.

Friends do not let friends send frothy oil through bearings.

Beware of marketing and well marketed products that have a cult like following.

If you want thicker oil to address low oil pressure at hot idle, buy thicker oil.

If you want to sell a vehicle with a worn out engine whose oil pressure reads too low, add lucas oil stabilizer to whatever is in the sump, polish your teeth and practice holding eye contact whilst lying.

Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751612
August 14th 2019 1:40 pm
August 14th 2019 1:40 pm
Joined: Jul 2019
Posts: 38
Ohio
M
Mikeburkey Offline OP
newbie
Mikeburkey  Offline OP
newbie
M
Joined: Jul 2019
Posts: 38
Ohio
I do not plan on ever selling the van. I also plan on fixing everything my self as it needs fixed. I will be buying a tach soon and installing it. Other than the oil pressure being low when the engine is hot there are zero problems. No engine noise, nothing. Very smooth and it hasn't given me any problems. I don't doubt there actually isn't any problem.


Chevy Van G20 3/4 Ton 5.7 L 8 Cyl
Re: Oil pressure drops to almost nothing at idle when hot [Re: Mikeburkey] #751659
August 16th 2019 1:17 am
August 16th 2019 1:17 am
Joined: Apr 2010
Posts: 2,685
San Diego
W
wrcsixeight Offline
veteran
wrcsixeight  Offline
veteran
W
Joined: Apr 2010
Posts: 2,685
San Diego
A tach is great. The Op gauge reading low, does not mean the OP is actually low, especially if no noises start when idling at hot idle speed.

I installed a mechanical oil pressure gauge well before I installed a tach. Both respond to rpm similarly with hot oil, when cold the Op gauge pegs at 66 to 68PSI and only begins to drop at lower rpm once the oil warms, and hot as it gets with 10w-30 at 525 rpm is 19 to 21PSI.

My OEM OP gauge still works as I T'd the line. the OEM gauge does not really correspond to the mechaincal OP gauge. there is a 45 second delay and much less of a range. So PSI reads one hatchmark above the bottom, 68 PSI reads just over half.

So do not put much faith in the OEM OP gauge. Its likely a bipolar liar on an overdose if Diazapam, looking for attention.

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