Motor Health

[88-GT]

Hey guys.

Time has come to dive into the motor and Im trying to decide if a whole new long block is in order. The original motor in it has 200km, around 120k miles on it.

The thing runs like a top, starts good, runs strong, idles smooth and doesnt lose any oil from change to change. Honestly, it doesnt move off the full line over 2500 miles. It also has good compression, well below 10% variation over all 8.

Problem comes with the oil pressure. I have a mechanical guage and from trial and error I need to run 20w-50 in it just to keep pressure at idle. Startup it will usually sit at about 55(relief), but once warmed and after a little spirited running, it will drop down to just over 20lbs at a 750 idle.

I was planning on just swapping a TFS top end kit, with supporting mods on this short block, but am starting to have second thoughts. So what do you guys think?

Thanks in advance, Adam.

 

[5.0Droptop]

I would freshn up the bottom end. rings bearings and new oil pump. 120 k isnt anything on the 5.0 block

 

[NKau]

Where is the oil pressure at when you're cruising? The general rule is 10 psi for every 1,000 rpm you are turning. With heavier oil like 20w50, if you aren't seeing that, you may want to at least replace bearings. Do you have an aftermarket cam by chance?

 

[86bluecobra]

20 psi at idle is fine. I know i get worried when my car sits at 30 psi at idle. I know where you are coming from but that oil pressure is O.K.

 

[Fast63]

what is the oil pressure at hot idle with regular 10W-30? 20 is absolutely fine, even 15 is ok. 10 is probably borderline and time for a rebuild. These engines really do not require tons of oil pressure.

 

[blackened88lx]

I would freshn up the bottom end. rings bearings and new oil pump. 120 k isnt anything on the 5.0 block

I agree. While 20psi may be acceptable, it's definitely not quite what it should be for one of these engines, especially with oil that thick. Seeing how it doesn't burn any oil and compression is good, you could pass on the rings, but that would be kind of pointless seeing how you're going to tear into it anyway. You should be fine with rings bearings and an oil pump, and slap the TFS kit on when you put it together.

 

[Darkwriter77]

Port your heeeeeeeeads! Motor health will drive ya' maaaaaad!

(Sorry, saw the title and couldn't resist. )

FWIW, my '89 notch with 270k on the clock (now Frankenstang's) would sit at around 20 psi at idle with 10w-40 oil when up to temperature, and slightly higher (23 psi?) with 20w-50. The motor was rebuilt somewhere around 150k miles and doesn't use a terrible amount of oil (maybe two quarts between oil changes), and there have never been any knocking or clacking valvetrain/bearing sounds at any point.

I'd say you're safe at 20psi @ 750 rpm. As mentioned above, I'd be more concerned if the pressure doesn't pick up to where it should be at cruising RPM's, as that would indicate you've got a bottleneck somewhere - clogged pickup screen or something along those lines - although you'd probably be seeing some symptoms on the lower end of the RPM range, as well.