i have a 400 small block chevy out of a '72 chev. caprice. put it in my '78 camaro. when i start it up and it warms up to operating temp. my oil pressure will only read 5 psi. when i'm driving down the highway it gets up to 20-30 psi. Also once i'm driving it , and its warmed up, when i come to a stop at a light, the engine kinda chugs a little bit, and sometimes dies. it always starts back up though. A couple days ago, i noticed it was starting to leak oil from the front of the intake manifold and also from the timing chain cover where it meets the oil pan. My question is this, could the oil leaks cause my oil pressure to go down, and also cause the engine to idle rough? or do i need to replace the oil pump? the guy i bought the engine from, said he put a high ov oil pump in it when he rebuilt it, and said he had only put 500 miles on the engine after rebuild. he also said he put a used cam in it, and that the valves may need to be adjusted, i have done that already. If anyone can help me, or have any suggestions as to what it might be, i would greatly appreciate it.

thanks
chevyguy78
chevyguy78

Ok: I'll try at this and should know exactly and don't - sorry. The timing cover should be just crankcase area oils and vapors and chain is lubed by drip, splash or some spray - right? If so a leak there is just a leak and not hurting the oil pressure directly.

Your readings are lousy and dangerous! Most Chevs will spike to 65ish cold start and hover to 35+ when warmed up and idling and jump up when revs go up. I think the classic "idiot" lights, light up at below 20psi or so.

?? I just can't recall if the intake manifold is holding oil pressure thru it's gasket (momentary brain damage - sorry) but isn't the pressure gauge on the back - is it thru the intake or on the block?? I think it's on the block so the leak unless somekind of out of control is not the cause of low oil pressure.

Don't wait too long - it may be late already for this engine, hate to say it! Get a reading from a tester not involved with the vehicle's own sensors now.

Running at the 20-30psi it probably would behave and when it drops down to 5psi that's not enough to keep bearings pressured up such that they effectively aren't touching AND the lifters need oil pressure to hold their position or would start to collapse, ticking and running rough would be noticed. Chugging could be plain friction and lightening speed wear on the engine!! The oil leaking could be from excessive blowby already in the crankcase area, anywhere and would find any opportunity to spit out oil whether misty oil, splashed or whatever.

Oil pump must pressure up the bearing first and if they leak down too much it can't go on to the other items throughout the engine. Cam has been replaced - what happened there?

I doubt the oil pump itself is the trouble. At this point this may be an autopsy instead of what to repair now, unfortunately

Ideas guys??

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/

the story behind the engine was they supposedly did a mild rebuild if you say. they said new bearings, rings, timing chain & gears, and a new oil pump, and put the used cam back in. It was put into a k-5 blazer where he said he put 500 miles on engine then sold blazer but kept the engine when i first start it cold it does jump up to like 60 psi, and pretty much stays there till warmed up then eventually, it will slowly drop to 5 psi and jumps when revved up. The gauges are sun-pro that i bought from autozone and installed myself. When driving or at a stop i do not hear any ticking just rough idle. and only sometimes it dies.... the engine was a 2 barrel engine and now has a holley 4 barrel on it. don't know if that makes a diff...
chevyguy78

(This post was edited by chevyguy78 on Mar 4, 2008, 8:19 AM)

Your gauges are probably right on the money by the symptoms along with the readings - just wanted to verify that.

The used can brings in some questions as to how good it was with it's bearings which are pressure lubed and if excessive wear it hurts the whole oiling system with oil going to the biggest leak even unseen internally.

This site is a blast as it makes me dig up old school days when we studied this stuff intensly - a good refresher on the priciples of the workings of things.

To draw a written picture of what's happening in this style engine and many, is like one of those garden hoses that you hook up to "X" amount of water pressure and volume that is made with pin holes to leak and water along its length. You engine's bearing are designed to leak a metered amount and sling the waste off for the other things that need oiling. Just like the hose picture if you made a few leaks way too big the others suffer and may not spray or get pressure or water at all - that happens in an engine too.

Side note: Sludge can plug the small ports for the oil and nothing beyond that plugged up port gets oiled as they go in sequence - that shouldn't be the problem with this engine if apart not long ago and cleaned up and with the sludge case oil pressure could real well where it's monitored and not good beyond that spot.

NoteII: As you know the bearings in the engine aren't rolling barrels or ball bearings. They merely don't touch by a film of oil under pressure between metal parts - in theory shouldn't wear at all if perfect. The forces are beyond comprehension at tiny spots throughout.

Carbs have nothing to do with this. The cam back when may have. The trick now is to figure out what to do about this now and I'm just not sure yet??

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/

ok, so i put new intake gaskets on today, what i also found out is that the engine after it was pulled, sat for about six months or better, before i got it. also, my oil pressure gauge had a leak in the line, fixed it a little better but still only 5psi at warm idle.

so, i was thinking about a new oil pump, but you think it might not be that, do you think i need a new cam?
chevyguy78

Help guys! I think the first to get oil are the main bearing and on to the cam which pushis oil up thru the lifters, pushrods and then it's all drip down.

Right now I guess I would try a new oil pump and ask for one with the highest volume output. Also - what rpm is this at when you see 5psi? If an engine is about to stall that might be in norms but I've seen oil pressure build to turn off an oil pressure light with just cranking speed and not yet running. If you are going to run this much at all I'd crank the idle speed up to where it shows some decent pressure right now and shut the engine off in gear if needed to prevent the run-on dieseling thing they can do.

The classic worn engine will make a low marbles knocking for a few seconds when just started - does it ever sound like that - the same as when you just change oil and the pump is filling the empty oil filter first type sound? BTW - fill oil filter with oil first when possible to minimize that time helps.

If this was about to stall from the low oil pressure and friction being the load then that's troule big time. I just can't know that and not sure how to know for sure from here or quite what to suggest right now. Therefore - try the oil pump and cross your fingers unless someone has any more ideas for testing or what might help??

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/

i changed the oil pump, still the same effect, just a tad bit more pressure. what else? Does it need new bearings, or a new cam or both? if something is possibly clogged is there something i can by like an oil additive that can maybe clean it out?

now i have another problem, i had put in a new thermostat, and and it was running fine, but now its overheating again, i had changed the water pump, but had put a used one on, do you think it may be time for a new one of those also?
chevyguy78

I don't know how long you want to run this for the overheat situation. Used pump would be fine if it fit and impeller wasn't rotted off. T-stat might be no good or air still in the system but those aren't the worst to burp out air. You can see coolant thru the end tank rad cap and it should flow well if level is just down a bit you'll see it. If hose doesn't warm up (top one) at radiator end the t-stat just isn't opening.

Oil problem- arggh! You probably want to take this engine out. I think the main bearings would take the biggest hit and you can "plastigauge" them with that which is a plastic stand that you put in where the bearing is under cap and torque - remove and match up how thick it got for the spec.

I really can't think of what could be gucked up that could cause this. It might not matter now if damage is done

A million years ago with totally sludged out engines the return ports under valve covers would plug up and all the oil or way too much would collect up there!! A real oold mechanic a long time ago used blanks for a rifle and hit them - they would blow out the junk! He could also make up a bearing with a peice of leather! I don't think you'll find that suggestion since perhaps the model T! Truth is if there was that much sludging the engine is toast.

What do YOU want to do. I really don't know what else with what I've seen so far on this. Perhaps the other guys have some ideas. I'm about out and if mine would probably bail out on the motor - bummer

T
Tom Greenleaf - MetroWest Boston - USA
_________________________________________

http://www.autoacsystems.com/tomgreenleaf/

I had a problem similar on a small block Mopar. The machine shop milled my heads by .030" and failed to surface the intake face. I had extremely low oil pressure and traced it to the intake gaskets on the bottom of my head/intake seal. It caused an overpressure in the crankcase making small oil leaks pore oil and make the engine idle and run badly. So my question is this, did you have the block or heads resurfaced during the build? If you did, I would be taking a good look there. Check your plugs and see if they have an oily coat to the tips. Also find a vacuum meter/gauge and see if you have a steady vacuum or if it twitches from side to side. Steady is OK if you don't have a wild cam in it. Twitching usually means a problem. Just an idea from my younger days.