Pine Barron

What is the ideal oil pressure for my 88 straight six? My manual is pretty vague. I installed a mechanical oil pressure gauge last night and here's what I got for oil pressures. Cold idle: 55psi Hot idle: 25psi Hot driving @2000rpms: 45 The reason I ask is because my truck has a knock on start up thats been getting worse. It seems to go away when it warms up but when stop and idle for a minute I think I'm starting to hear it then too. I've read some posts that say not to worry about this sort of thing on a straight six, but I had a small block chevy that sounded like this and it died shortly thereafter. It's got 142,600 with a recent oil change and a motorcraft filter.

1987 F-150 XLT 4x4

You have normal oil pressure for a 4.9L.

My 65K rebuilt and balanced 4.9L shows 42 psi at 2500 RPM and 25 psi at idle
on a aftermarket electrical gauge after warmed-up.

What is the weight of the motor oil you are using?
I use straight 30W year-round in Florida.

No engine should knock on start-up, the Main Bearings on the Crankshaft are worn.

As long as the low knocking sound quits after a few seconds after a cold start,
the 4.9L should last for years!

Pine Barron

Normally I run straight 10w30, but right now 2 quarts of it are 10w40 because I was low on oil and thats what I had at the time. It just leaking from the drain plug in the pan though...when I do my next oil change I'll put some teflon tape on the threads and that should fix it up.

If its got worn main bearings are there any additives worth using to make my engine last longer? I drive it like an 80 year old, but I occasionally tow a 4,000 pound trailer. Is that ok?

Just call me Sean

I drove my truck with the I6 for over a year knocking. The knocking didn't even kill it, the blown head gasket did but even then it still ran.

1987 F-150 XLT 4x4

No, there are no additives to help worn main bearing.

I have owned several I6 300ci 1V from the 70's,
couple of them had a low knock on cold start-up,
but held normal oil pressure at highway speeds;
I used 20W50 motor oil and run the engine for years with no problems.

Tow your trailer, it won't hurt it, just keep checking your oil level regularly.

Yeah, Teflon tape is good stuff,
but for a few bucks you could buy a new drain plug with a new gasket;
either way, as long as it stops the oil drip.

-----------------------------------------------------------------------------------------------
I went back and re-read your first post again-
If you hear the knock after it's warmed up now,
you can buy the engine some time running a thicker oil, it will last longer.
Seriously, you will not hurt your engine running 20W50 oil in it!


Hope this helps!

Just call me Sean

The oil drain plug should have a nylon washer that seals it.

dr_bowtie

just run it....

It is typical of Fords to have a Main rattle when cold....the oil drains back to the pan when cooling and the rattle is the lack of oil for the few short seconds until it pumps back up....

even the cheap motorcraft filters dont stop drain back...you need the better 10.00 dollar filters...

Mine started doing it the very first oil change I did when I got the truck at 79,000 miles when I put on a 3.00 dollar motorcraft filter....and I even use good Royal Purple oil

Pine Barron

I'd say the knocking takes about 5 minutes to stop knocking, not until the truck is totally up to normal operating temp it seems like.

Also mine is missing that nylon washer...have to pick one up.

I guess I'll just run it until it gets too bad and then maybe learn how to rebuild a straight six.

Just call me Sean

It'll still run forever knocking away.

Kubb 147

Is it a low knock or a light tap? These engines are known to tap alot cuz of the rocker arms. Gotta retorque them.17 to 23 ft lbs. Try that first. I gotta do mine. They are tapping alot.167000 miles.... Id say it was time LOL. Besides I need to put a new valve cover gasket on her anyway. I been slackin...