Low Oil pressure after restarting hot engine...??

[jpstiles02]

Hey folks



Last week I replaced my '66 Ford F-250 w/ 352 V8 intake manifold gasket, changed oil & filter ran for 5 minutes, then drained and filled w/ 15-w40 Valvoline Diesel Oil & FL1-A. On cold starts, my oil pressure is perfect 50-60 psi, comes up right away. After truck is good and warm (on H of Temp Indicator, used to be on C before intake gasket change, replaced w/ a 180º thermostat because thats what Advance Auto Recommended.) Anyhow, I shut it down for 20 minutes or so and when restart oil light stays on for a good ten seconds w/ 10-25 psi oil pressure, then starts to come right up to the normal 60 psi. Whats going on here???

Thanks!

 

[skyship]

Low oil pressure at idle when hot could be Black death (SLUDGE). I don't know this engine, but in general terms you need to take a look inside to see if it is nasty, sometimes that can be done through the oil filler cap, or if you just switched to a high detergent or High Mileage oil then cutting the oil filter open will also show deposits, but if the low oil pressure light is on then that is serious, so you need to find out if it is sludge asap. The other possibilty are overheating, extreme wear or low oil level as a worn oil pump is unlikely.

If it is a case of Black death, don't play with engine flushes that you drive around with, as they are real dodgy. Take the sump off, clean it and in particular clean the screen on the intake for the oil pump. You should take the top off and then clean out everything possible, but if you don't want to pay for that long nasty job, then take a slight chance and use a can of Liqui Moly sludge remover which is just used at idle for 10 minutes before changing oil and filter. After that use a cheap filter and basic conventional oil, go for a drive to warm the oil fully but avoid high revs and repeat the procedure.
After the physical clean and idle flushes, use an oil with lots of detergent, like a major brand fully synthetic or one of the High Mileage oils if you also have an oil consumption problem.
Sludge is caused mostly by poor quality supermarket oils or simply not changing oil & filter often enough.

PS. Which oil filter are you using because it is also possible if this problem just started after the OCI you have fitted a bad filter ??

 

[default]

Drain back valve?

 

[jpstiles02]

FL1-A Motorcraft. If I drop the oil pan to clean intake screen, should I might as well change the oil pump?

 

[skyship]

I don't know the history of this engine, but an oil pump takes a very long time to wear out. Double check the oil filter is the correct type and if does not include a pressure relief valve and the engine has a bypass valve it might just cause a drop in oil pressure if it sticks open after cold start, but that is a rare fault.

If the sump is fairly clean and the intake screen to the oil pump not partially blocked then I would be inclined to get a compression check done to see what the main block condition is. Ford must have a classic trucks forum and they might well be able to figure out what might be wrong and give you an idea of repair costs.

If you were doing an annual UOA, a worn oil pump shows up as an increase in Fe contamination, BUT without Pb, Cu or Cr, so it is only the Fe that increases due to the spur gears breaking up. You can figure out if the oil pump needs to be replaced by measuring the gear to case clearances to see if they are in limits and see if there is play on the shafts.
Normally a failing oil pump will make a whining noise, the lower oil pressure causes various rattles to increase and in a severe case the engine starts to run hot, but the oil warning light will normally be on by that point. Sludge is a silent killer!

 

[Trav]

Quote:
on H of Temp Indicator, used to be on C before intake gasket change

Is the temp gauge pegged out on H?
Did it do this before the intake gasket change?

 

[TFB1]

Originally Posted By: jpstiles02
Anyhow, I shut it down for 20 minutes or so and when restart oil light stays on for a good ten seconds w/ 10-25 psi oil pressure, then starts to come right up to the normal 60 psi. Whats going on here???

Thanks!


What you've posted doesn't follow suit with any of the FE (352-428) engines I've owned over the last 45 years... The light should be going out with more than 6-8psi OP, if not you have a defective sender... Hot idling oil pressure on a FE is rarely more than 25psi and usually less...

If it has no oil pressure for several seconds on restart try another filter, possibly the anti drain back valve is defective... I've never had the problem with a Motorcraft filter but did have issues with a Purolator Classic...

 

[mechtech2]

Could be the sending unit, or it's passage being partially plugged.

 

[jpstiles02]

Not pegged out on H, just at the H, used to be right apast the C before intake manifold change...