GMC Repair: Oil pressure, gmc vandura 2500, gmc vandura

Question
QUESTION:  have a GMC Vandura 2500. 350 5.7 Liter. I have noticed that the oil pressure is around 20. It is usually 30. Lately it has been jumpy. 10-40. Sometimes close to the red. One day the temp went up to the red and at the same time the oil pressure went down into the red. but only for about 5 seconds. The Jasper motor was a replacement motor (new) and has about 50k on it. We changed the sending unit and the pressure seemed lower with it so put the old one back on. We tried the sea foam. no change. still erratic. Any suggestions? Oil pump going bad? I need a muffler. it isn't loud yet but making a popping noise and rambling.

ANSWER: Hi
not knowing the exac year, it is VERY likely either the gage or the wiring from sending unit to the gage may have excessive resistance.
My best advice, since it is a van, would be to attach a manual live gage on the engine and watch the ACTUAL pressure.
This will tell you if it is a gage or an actual pressure problem.
I Hope this helps.
Please follow back post, if needed.
Pawl

---------- FOLLOW-UP ----------

QUESTION: K well I am leaning toward the muffler being the problem. I had it changed today and all is better for the most part.It was clogged. Changed the already fresh oil and put some Lucas in with it. (and another new purlator premium filter)PRESURE IS GREAT 30-40! BUT I am still hearing a LIGHT, ring, rattle comming from the oil pan area.I am taking my children to Flordia Saturday from Indy. The Motor has about 50k on it.WOULD YOU CHANCE IT? THINK IT IS THE BARING? THANK YOU FOR ANY ADVISE YOU CAN GIVE!

Answer
Hi
It is VERY difficult to diagnose noises not having vehicle here.
I would tell you to go with your gut feeling. If it sounds bad enough to NOT go OR if you'll worry the whole way, then dont go.
Take it to the shop that installed muffler and see what they say.. That would be the best advise is to have a real set of ears listen to it.
I hope this helps.
Good Luck either way.
Pawl