I have an old work van, that I built a new engine for a while back. it's got about 4k miles on it now.

It has great oil pressure when I start it cold; around 55psi at idle, 60-65 at cruise until warm. Once it warms, i drops down to about 10psi at idle, and 45 or so at cruise. Doesn't sounds like it's got lifters ticking or any knocks, etc.

Is this just a symptom of oils nowdays? Or is it maybe something with pump/regulator? It's got full synthetic in it, but did same thing with conventional. I swear my ol mustang is a consistent 45-50psi all the time.

I don't think it's hurting anything, but just seems odd to me that it'd drop like 45-50psi at idle. Now it is the factory gauge, so it could be off some as well; i haven't put a mechanical gauge on it yet.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

if shes happy run with it, i would maybe kick the idle up a tad if the pressure follows

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http://www.efidynotuning.com/ford/

That's a sign of excess bearing wear.

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89 Coupe- Canfield 195's, Holley Systemax II, CI cam, 24# Inj, 05 Slot MAF, 75mm TB
BBK 1 3/4 LT's, 3"Exhaust, 3"Spintech's, T-5 Trans, QH 1.4, AEM WB, BE/EA: A9L-GUFB

that's what I was concerned about. It's a brand new rebuild, but was a used crank i got free, as the old one was shot. But we mic'd the crank, and plastigauged it when we installed, and it checked out fine...

Saw a few other places that it's not uncommon for chevy's, but still kinda concerns me.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

This is my opinion, which may not be worth spit. But here it is.

As long as you only see PSI drops at idle RPMs, I wouldn't be terribly concerned about it.

Lubrication isn't done via the oil pressure. Oil pressure is only necessary to get the oil to all places in the engine that need oil. But once the oil is there, the presence of oil on the surfaces is where the lubrication comes from. Under heavy RPM/Loads, there is a lot of slinging about of parts and a lot of squishing together of friction surfaces that tend to squeeze the oil out so you need a ready supply of oil available to rush in when possible. That's all the oil pressure does. But don't believe the oil pressure produced by the pump can "force open" the gap between the rod bearing and crank. There's FAR more pressure between them than the oil pump could possibly work against. What protects metal under load is a sufficiently thick enough oil to stay in place until the end of the power stroke and a sufficient quality oil to resist sheer & breakdown. Oil sheer is the high speed ripping effect that literally strips metal surfaces clean of the oil allowing the metal to rub bare. Fortunately most oils have sufficient anti-shear characteristics today. But the best resistance to sheer and breakdown are from synthetic oils.

The way sheer was described to me is imagine taking a fresh piece of chewing gum and stretching it as fast as you can. When you do so, it stretches and stays together with relative ease. But chew on it a while, the softening agents get chewed out leaving the gum rubbery & tough. It won't have the same ability to stay together if stretched really fast. Try to stretch it too fast and it doesn't just resist you, it literally snaps into 2 pieces. The surfaces completely sheer from each other. At high speed, oil will do the same thing. And just like with the gum, the thicker the oil is, the more prone it is to sheer. So it's a balancing act of starting with a thick enough oil to stay between the friction surfaces, a thin enough oil not to sheer, and of course a combination of oil blends, additives, and detergents to continue to do so. But generally speaking, additives and detergents are a help up to a point. But you only want as much as is required and no more. Only the oil lubricates. So the more other crap you get in the oil, the less oil molecules you have lubricating hence why study after study shows oil additives are an absolute waste of money. If you want to do something beneficial for your engine, change the oil on a regular basis and use synthetic. It's as simple as that.

However as someone said, the fact that this is happening may be an indication of a problem that does need attention or need to be fixed. Or it may just be what this engine does. I couldn't say to that.

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...Always Somethin'

89 Ranger Supercab, 331 w/GT40p heads, ported Explorer lower, Crane Powermax 2020 cam, 1.6RRs, FMS Explorer (GT40p) headers, Slot Style MAF, aftermarket T5 'Z-Spec', 8.8" rear w/3.27s, Powertrax Locker, Innovate LC-1, GUFB, Moates QuarterHorse tuned using BE&EA

Member V8-Ranger.com

I agree that pressure isn't the holy grail when it comes to these things. But don't look at it as just a number. Use it as a tool.

45psi drop in 4k miles is not acceptable. It clearly indicates an issue. Like bearing clearances enlarging. An engine that is properly wearing should only drop 5psi and 10 at the most. Last engine I put together, idled at 35psi warm at 750rpms. I probably have 6k on it now. At it idles at 30-32psi warm. Cruise was about 60psi and now its around 58psi. And I flog it every chance I get. Even when its not warmed up. I'm very hard on my engines. And oil pressure is rock solid and almost where it was when it first turned over. The old engine it replaced had the exact same symptoms as the poster does. 8-10psi warm, and 35psi at WOT. I drove it like that for years. And beat the crap out of it too. Every drive it went on.

When I tore it down. The rods looked good. Mains had groves in the crank, and grooves in the bearings. With issues like that. You can't expect the same weight oil to be sufficient for the high and low spots the grooves created.

It may not be his issue. But the numbers look identical.

Another possibility is diluted oil.

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89 Coupe- Canfield 195's, Holley Systemax II, CI cam, 24# Inj, 05 Slot MAF, 75mm TB
BBK 1 3/4 LT's, 3"Exhaust, 3"Spintech's, T-5 Trans, QH 1.4, AEM WB, BE/EA: A9L-GUFB

What was the warm idle pressure when you first put it in? I don't see you say what is was like originally. If it was the same, you're probably good. If it's gone down significantly, then like Joe says. Chris's explanation is very good.

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85GT, 302 w/Dart Windsor Jr heads, Crane 2030 equiv. Performer 5.0, 75mm TB, 88mm slot MAF, 34lbs injectors, BBK shorties, 5spd converted to 4R70W with Baumann controller, 9" rear w/3.25s
A9L running A9P bin via Quarterhorse w/LC-1 WB

The Cam Bearing are the problem!!!!!!

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94 Cobra,stock block, HP single turbo kit, 6lb spring, blowing through full mufflers,05 slot HPX 3"tube blow through,255lb in tank , 42lb Muti tech?? ( who knows what they are, they came from Summit)style injectors,Mcloed street twin, TKO 600 tranny(shifts terriable), 3.08 gear , CBAZA.BEB from Pops Racing J4J1 w/ quarterhorse, BE/EA, AEM wide band, and boost gauge.MSD6

Has anyone asked what the bearing clearances are and what weight oil he is running yet?

Thanks for all the input guys.

I am running 10-30 full synth. oil has aprox 4-500 miles on it. I had standard 10-30 oil in before that, for break in. It behaved the same.

The pressure has behaved this way since the beginning; so it hasn't actually dropped 45psi from start, it more likely has dropped 2-3psi from original pressures. But it's the drop from cold to warm that gave me concern. Cold idle = 55psi, warm idle = 10psi. Cold cruise = 65psi, warm cruise = 45psi.

I don't remember exactly what the bearings clearanced at, but it was within factory specs.


tvsn94... Why do you say Cam Bearings? We did also change cam bearings, and put in a new cam. So this was one of the other things that I had suspected. Hydraulic flat tappet cam. New lifters as well; supposed to be factory replacement and felt right putting them in (no excessive play).


Again, thanks for the input folks. It may not be anything to worry about, but I'd rather err on the side of caution, especially with a fresh engine, on a work vehicle.


When I get time, I'm going to try and drop the pan and check bearing wear. It's easy to do on this platform, so again better safe than sorry.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

if you changed the cam bearings and bugger them up putting in the cam, then the clearance is suspect.
seriously, people do rebuilds and ignore the cam bearings ALL the time . it only shows up when the engine is warm.

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94 Cobra,stock block, HP single turbo kit, 6lb spring, blowing through full mufflers,05 slot HPX 3"tube blow through,255lb in tank , 42lb Muti tech?? ( who knows what they are, they came from Summit)style injectors,Mcloed street twin, TKO 600 tranny(shifts terriable), 3.08 gear , CBAZA.BEB from Pops Racing J4J1 w/ quarterhorse, BE/EA, AEM wide band, and boost gauge.MSD6

I'm sure it will be fine but we have a saying here at the shop. When in doubt, check it out. Well, actually we say yank it out but you get the point. If the bearings look fine and you are still a little queasy about the pressure use a thicker oil.

My dad works as an engine builder and I had him install the bearings, he showed me how to use the installation tool and about how you have to keep them real squared up and line up the oil holes, etc. So I'm sure the cam bearings are installed properly. cam felt real good and spun nice and free when it was in.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

yeah that was my other thought, maybe changing to 10-40 or 20-50

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

Did you check the oil and filter for metal?

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91 GT
347 Sportsman Block, Scat internals, TFS R heads and intake, Aeromotive sumped fuel system, D1sc Procharger, 90 MM ACCUFAB TB, 90 MM lightning MA, Electric Fan, 60 #, Tweecer with Innovate LC-1 WB and TKO 600 Trans

yep when i changed oil last, i ran the oil through a paint filter and didn't find anything, and cut the filter apart and didn't find anything. that was after about 2-3k miles.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

if your gonna yank the pan it would be foolish not to throw a high volume pump in with new arp shaft

_________________
http://www.efidynotuning.com/ford/

Is a brand new pump. It's not a high volume, because the stock pan on it isn't real big and don't want to risk starving it (though probably wouldn't in my rpm range). Don't really need a better shaft as it won't ever see more than 4500-5k rpm.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm

Before you start pulling the pan, have you ensured 100% with confidence that the oil plugs on the main galley front and rear where sealed with the correct plug? Very common to miss these in a SBF v8.

Thanks, this is an SBC. and they were plugged correct, pulled the ones that were in it to clean, then reinstalled. Got a mechanical gauge to check pressure for sure this weekend. Then may pull the pan; not sure yet.

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1978 Mustang II King Cobra
89 5.0HO, Stock Short Block, Edelbrock 4bbl aluminum intake, Holley 650 double pumper, MSD 6AL, Ford F303 cam, 1.7:1 Crane Roller Rockers, Pocket Ported stock heads, Hedman Long Tube Headers
5 spd Manual
Full roll cage, 9" full floater w/Currie trac lock/373 gears, RCI Fuel Cell
Project Page: http://www.brandttuning.com/projects.htm