View Full Version : Oil Pressure
03-30-2011, 12:15 AM
I did some engine work recently, planed cylinder heads and exhaust manifolds to correct leaking, replaced oil pump, new water pump, new head and intake manifold gaskets.
My oil pressure is fine when I start but seems to disappear when the engine is warm. I have a mechanical oil pressure gage and it shows low to no pressure. I know I have oil pressure because the engine runs fin, no metal on metal noises as if there was no oil in the system.
Do I have a vacum leak somewhere I am missing?
03-30-2011, 12:38 AM
Friend of mine have the same problem. It turned up being the brand new pressure guage that was not working.:o
03-30-2011, 03:37 AM
John, I'm with Anders.
Before jumping to conclusions, buy a cheap oil pressure gauge and screw it into your engine. There are plenty of places around the oil filter, or you can unscrew the oil pressure sending unit temporarily.
Let us know what the readings are.
I know you changed your oil pump, but we get overly cautious about the oil pickup screen getting clogged after many years and many miles. Please don't run your engine fast or far if you suspect low oil pressure.
03-30-2011, 07:00 AM
You have a common issue found in the FE block, it may or not be a problem though. Ford's spec for hot idle oil pressure was 5lbs, what they don't spec is the flow. What you probably have is a worn crankshaft and bearings, worn cam bearings, and worn rocker shafts. If you installed a standard capacity oil pump you could still have low pressure at hot idle, but oil is flowing! After verifying what the pressure really is by putting your test gauge in the top of the oil filter housing where the sender is now, you can determine how low is low. If you're not ready to fully machine the block and crank, a heavier weight oil might be enough to calm your nerves ;) Here's a link to a good article on FE oiling, it's universally accepted among FE builders. Good luck, Bob C http://gtscode.residentsystems.net/feoil.htm
03-30-2011, 12:02 PM
Pick up a Melling M57HV oil pump. It's about $60 from most places. This is a high volume oil pump and will take your pressure up quite a bit at idle (mine is now about 12psi hot idle).
Did you restrict flow up to the heads? This can help as well. Did a machine shop work the block? If they did, did you check that all the oil plugs are in place?
Like the last post said, the FE's are known to have a low pressure at idle, and the manuals even say not to worry about a flickering light at hot idle. It is disconcerting on a new rebuild though.
03-30-2011, 03:59 PM
I just got off the phone with a friend of mine, John Vermeersch (we both worked at Ford Motor for many decades). John is my FE Guy. He isn't too worried about 6-psi at hot idle as long as you have at least 30-psi at 4,000-rpm in a daily driver.
Here's a quote from John regarding FE oil specifications:
"The Ford shop manual 1970(has Boss 02/429/428cj/scj/429cj/scj)great ref. material.....correct psi is 25-60 lbs @2000rpm HOT...minimun psi is 6lbs at 400 rpm ,lifter collapse,valve train noise.Bearing clearances of .0025/.003 will result in 10-15 lbs at hot idle, and 65lbs at 2000..."
Notice his last sentence. Opened bearing clearances of .003" are for racing engines.
A word of caution regarding 'high-volume' oil pumps... I have had problems with them as they put excessive load on the cam gear and as a result, can fail prematurely. If you use one, you might get up to 10-psi at hot idle. - Dave
04-04-2011, 02:31 PM
Thanks, Dave. This is good info and there seems to be such limited explanation in the manuals. It gives you some indirect information of the state of the engine also. And the oil pressure light comes on at about 7 psi and below, correct?
04-04-2011, 02:40 PM
I had my 390 rebuilt in '07. I had the machine shop open the main oil passage to just under .5", a high volume oil pump, std/std crank, .060" overbore, balanced the reciprocating assembly and all new internals. I also restricted the flow to the heads. I have 40-55 psi at hot idle, and 75+ at cruising rpm. (over 100 when my foot is heavy).
I am running an electric oil pressure gauge.
04-04-2011, 03:16 PM
As a "shadetree" tech, I've always read 10PSI of oil for every 1,000RPM is the safe level in a healthy engine. Once you start adding hi-volume oil pumps, etc, that number changes...
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