Oil pump replacement?

[gtmud]

I am about to do the rear main seal on an 88 4.0 w over 180K. The oil pressure is a bit low once it warms up. Was wondering, since I have the pan off, would it be a good idea to put in a new oil pump, if so should I just replace it with a stock pump, or should I be looking at a high volume?pressure type pump. Want to get more life out of the engine. Thanks in advance.

[Saudade]

What's "a bit low"?

[gtmud]

When its warmed up the guage reads at the first hash mark on the guage after the "0" mark. Has a new sending unit. When cold, it reads well above the "40" mark, more like near the hash mark after the "40" indication.

[JDPascal]

hi ya gtmud

It should be easy enough to hook up a mechanical gauge to the sending unit port on that I6 engine. That will give you the best indication of the actual oil pressure....

Just one caution about putting a new oil pump in an old worn engine..... The increase oil flow may contribute to an increase in oil consumption due to the extra oil throw off from the bearings onto the cylinder walls. The worn rings will likely have trouble keeping up with the extra work. This will be especially true with a high volume oil pump in a worn engine.

In most cases, high volume oil pumps are a waste of horsepower that it takes to move the extra oil that is only dumped back into the oil pan through the regulating valve. The one application where the extra volume is necessary is in a loosely set up engine for drag racing and the extra clearances need the volume to maintain adequate oil pressure.

One last question....... What viscosity oil are you using??

JD

[I6whitejeep]

Originally Posted by gtmud

Was wondering, since I have the pan off, would it be a good idea to put in a new oil pump, if so should I just replace it with a stock pump, or should I be looking at a high volume?pressure type pump. Want to get more life out of the engine. Thanks in advance.

FYI, its real fun replacing the pump. Hope you have a lift. Keep in mind, the Hanes manuals etc tell you to pretty much drop the entire front end, the stabilizer bar, and remove the bell housing cover. To pull out the pump, I found you really dont need to do this.

Here is what I did to pull out my pump. Remove the starter, as this will help get the oil pan to drop somewhat. Once the pan is dropped, you can then get at the 2 bolts to remove the pump. Let the pump drop into the pan, and then you can pull it out.

I am replacing my pump, long story, with a high flow one from NAPA. Its a good days work.

[gtmud]

I think its a straight SAE 30. So what your telling me is to just replace the rear seal and leave the pump in place? That can be done, just was trying to get as much life out of this engine as possible with out having to rebuilding the engine. $$$.

[gtmud]

I am thinking that if I undo the shocks and the sway bar I should be able to get the front axle to drop enough to get the clearance I need to get the pan out. However, I started it up today and it took awhile for it to build to even #40 lbs. Could this be because of a really leaky rear seal?

[JDPascal]

Originally Posted by gtmud

I think its a straight SAE 30. So what your telling me is to just replace the rear seal and leave the pump in place? That can be done, just was trying to get as much life out of this engine as possible with out having to rebuilding the engine. $$$.

Originally Posted by gtmud

I am thinking that if I undo the shocks and the sway bar I should be able to get the front axle to drop enough to get the clearance I need to get the pan out. However, I started it up today and it took awhile for it to build to even #40 lbs. Could this be because of a really leaky rear seal?

SAE 30 is a bit on the heavy side for start up and could be the reason for the slow pressure build up. I would try a 10w40 oil and see what it does. Also, if the filter anti drain back valve is not holding oil in the filter while the engine is off, pressure may build slowly while the filter fills. - Any valve/lifter noise while pressure is building??

I'm not saying to forget the pump, just know what the effect in a worn engine might be.

An oil pump should be a quickly accessed part for you. You could take the pan off to fix the leaking rear seal and while the pump is out for that work, pull the cover plate off and check it out with a feeler gauge like it shows in the manual while you look for scoreing on the gear lobes and in the gear cavity. If it is good, you might be wasting money on a new one.

The only other unknown in the oil pump is the pressure regulating valve (relief valve). If the spool is sticking or the spring is excessivly fatigued, that could be contributing to the low pressure too.

If you are interested, you could pull a main bearing cap other than the back one where the seal is and check the bottom shell to see if the babbit is worn thru to copper. Same for a rod bearing only check the top shell. I know you know to torque the rod and main bolts to spec when you put it back together.

If the crank journals are in good condition, you could roll in a new set of rod and/or main bearings while the pan is off too. Each set wouldn't cost much more than the oil pump and then you are done with it...


If the bearings aren't worn down to copper, a new pump might be the best idea for the price ($50 or so). Even if they are worn down, weigh the benefit of more oil pressure and the potential oil consumption situation.

Lots of options here - maybe too many. Hope I haven't confoosed the situation too much.

The leaky rear (or front) seal won't have any affect on the oil pressure.

JD

PS What ever you do with the pump, pack the old one with vasaline if you wind up putting it back in to make sure that it will prime. A new pump should be spun in a pan of oil before you bolt it to the block to give it a better chance of priming when you first crank the engine.

JD

[gtmud]

Thanks JD. I have 2 88's. Well the one I'm working on is a friends, same friend I got the other 88' from. The pump issue is on my friends 88'. Heres a more accurate description. 88' #1 (mine) with 218K, SAE 30, new oil sending unit will register oil pressure quickly. However 88' #2 (friends) was taking for ever to register above 40 lbs. and I heard a "knocking" sound, almost hard enough to think bottem end. Once pressure built up and 5 minutes of running "knocking" went away. I think you might be onto something with the filter valve, no idea when the oil was changed or what type. I'll inspect the rods and mains like you described and see what I find, also can I access the regulator spring to replace or at least clean? Funny, 88' #1 had a very bad over heating problem and it runs better than 88' #2 that didn't with a little less miles. Well as soon as I get some desent weather here in NC I'll tear into it and let you know what I find. Thanks for the information, very much appreciate it.

[JDPascal]

Just another idea that now comes to mind--

The pickup tube screen could be plugged with sludge or something else.... That would also explain a slow pressure build....

Take notice when you pull the pan....

JD

[Saudade]

I run 10w30 in my 88 (160K). Pressure reads just about 40 when just started and cold. Drops to about 15-18 (just below first hash mark) when hot at idle. I did the rear seal (not too long ago) and cleaned the pump screen. Didn't have a pressure problem before though, just a bad leak.

Your knocking could be from excessive clearance of a crank or rod journal that decreases once the engine warms up. The extra clearance could contribute to low pressure.

JD's got the right idea of checking them when you've got the pan off. You might try a mech stethoscope (or long screwdriver to the ear) to see if you can locate the source of the knock before you rip it apart.

Good Luck.

[gtmud]

Ok. here's the skinny on this subject. First, thanks for all the inputs, very helpful. Well I did tear it down, found that with the suspension unbolted and a 1/2" extension the pan came out(with the pump unbolted) I found what JD thought might be the problem, there was a lot, almost the entire screen, packed with "crystalized" crud. I cleaned it out, the pump looked good. Had one hell of a time getting the old gasket off( the pan too) recommend a heavy scraper for this. I pulled the rear main cap, was surprised to see that the bearing was in great condition.(181K and not even a hint of copper in the bearing face) Rods the same. RM was toast(hard as a rock) Reinstalled pan with one-peice rubber gasket and same oil pump( sucks having to buy the entire pump for just the gasket and no machine shop to press the pick up tube) Once it primed the pressure is immediate and on average start cold is 60+ psi. 20+ when warmed up. So a 2 day job ended in success, no leaks, now the entire engine is dry.
Thanks again guys for all the help and pointers. Oh just FYI, have any of you heard anything about a Tech school called UTI (Hot Rod U). WHat do you think of it. Thanks again. Ken

[I6whitejeep]

Originally Posted by gtmud

.... Oh just FYI, have any of you heard anything about a Tech school called UTI (Hot Rod U). WHat do you think of it.

Thats in Phoenix I believe. My Brother in-law got his Masters for Mechanical Engineering at WPI, then decided to goto UTI for his Auto Mechanics degree. He now does accident reconstruction for Exponent.. A job anyone of us wouldnt mind doing. Heh, his first day on the job he drove a MAC truck into a minivan..

From what he has spoken of it, he enjoyed his time there. The kid is a brain anyways when it comes to vehicles. He was born with an automotive brain... (must be nice)

Check it out.. from what I have heard, its great...