1991 GMC 2500 5.7 - need some advice

[clinebarger]

Originally Posted By: DoubleWasp


Pop oil filter off and change your filter adapter (which contains the filter bypass valve) for a new one.


An alternative is to plug the adaptor bypass with a 1/4" pipe plug & run a Duramax Diesel oil filter, Has a built in 15 PSID bypass. Acdelco PF2232 & Baldwin B1441 are a couple numbers.

 

[CBR.worm]

If the idle is dropping low enough for it to almost stall, the oil pressure will drop as well due low pump speed. Is idle speed too low? Does it stumble when returning to idle? Vacuum leak? Dashpot failure? Sticking throttle plate/IAC valve?

 

[bigdom]

Maybe change the oil pressure sensor

 

[sr17]

I finally got around to buying a oil pressure gauge. However, I found out that the oil pressure sending unit on my truck appears to be in a pretty hard to reach spot, so I have to ask what I realize may be a really stupid question - is there more than one spot on the engine where you can hook up a gauge?

The sending unit is located towards the very back of the engine, underneath the distributor. To get at it I basically have to remove the air filter and the distributor - then remove sending unit, attache gauge, reassemble to be able to run the engine - then go through the same deal just to remove the gauge and put back sending unit.

I guess I am just not super confident about doing this.

 

[Nick1994]

Crawl under the truck and do it

 

[sr17]

Originally Posted By: Nick1994
Crawl under the truck and do it


the location of the sending unit it on top of the engine, just hidden underneath distributor. Can's see how crawling under the truck will work, unless there is another point there to hook up gauge?

 

[Nick1994]

I haven't done one personally, but my brother has changed his sending unit on his 94 Chevy K2500 (5.7L) a couple times, I stood back and sort of watched. He climbed under there and replaced it within a few minutes.

 

[sr17]

Originally Posted By: Nick1994
I haven't done one personally, but my brother has changed his sending unit on his 94 Chevy K2500 (5.7L) a couple times, I stood back and sort of watched. He climbed under there and replaced it within a few minutes.


I've read somewhere that the location of the sending unit was changed around 1992. This video actually shows how it is done on my 1991 https://youtu.be/8n8YS6t3qn8

 

[HM12460]

IIRC, this vintage of small block Chevy had a plug in the oil filter head that could be removed with a 3/8" drive ratchet. Very easy to install a pressure line/gauge into this port.

 

[DoubleWasp]

1/4" ratchet, but yes, it is right above the oil filter mount.

 

[sr17]

Ended up just throwing in a new Delco oil pressure sending unit - no leak on the old one and no difference in the readings on the gauge. I know that I should have hooked up the mechanical gauge to know for sure what the pressure is, but having old and new gauge showing identical low pressure should be a pretty safe thing to go by - I think ?
Local parts store have a pretty good price on Lucas 20W50. Tempted to give it a try to see what kind of difference it makes in the oil pressure. Is Lucas good or bad?

 

[sr17]

I have started another thread under the appropriate heading to solicit opinion on the oil.

 

[csx7006]

The TBI engines are more bullitproof and easier to work on than the vortec 350.

 

[homeyclaus]

The 5.7L engines of this vintage had:

- leaking valve seal issues. This is likely your oil consumption, barring any leaks. The way to tell is if there is some soot at the end of the tailpipe. It won't be much.

- Low oil pressure needs a gauge, although the sending units like to go once in a while. Usually they fail open though, meaning you won't get the short one second oil light when you start it

- The piston slap you're hearing on a cold start is the hydraulic lifters taking up the slack. The rods and rockers get sloppy, and the whole thing rattles, especially when oil pressure is low

- thicker oil won't really help. The thing that would help is knowing the oil pressure, and then a higher throughput/new/rebuilt oil pump. It's two bolts once the oil pan is removed, it's tedious to do, but not hard

 

[Rob_Roy]

I suspect the low/stumbling idle is one of the main contributors to the low oil pressure light coming on. Check for vacuum leaks, check the timing, and consider replacing the PCV and idle air control valve.

Some sort of Xw-40 won't hurt anything, and may help. My brother has a '88 C3500 with the same engine, it has been pulling trailers for nearly 10 years with 15w-40 in the pan.