Doctor, we seem to be loosing pressure.


Senior Member
Ok, so blast away at ideas. I will post what I can that I have done, but any and all suggestions are welcome. I have the problem on my 93 Chevy K1500 4X4, 350 Z71 Off Road. Oil pressure is the problem, but not like that of most of the posts I have read.
Let's begin, I started noticing problems with the Oil pressure becoming low when it sat at idle and it has progressed over the months to when driving with the rpm is lower that 2000, this does not start to happen until the engine starts to warm up, pressure seems OK when starting cold. So I replaced PVC valve, tapit (sp?) cover gaskets, gauge, hoses, and such. After the cover gaskets were replaced pressure was back to normal, well at least for the first few miles, then went back to same problem, I also noticed that oil was leaking from the cover gaskets. After 3rd set of gaskets, I noticed what was happening. With gaskets replaced, I would have normal pressure until the gasket blew out. Either side, both sides, did not matter even the pvc valve would rise. So I had a 3 stage system flush done, EFI system flushed and rebuilt, Oil flush, tried standard and heavy duty synthetics, some of the over the counter treatments, and still the same problem. Engine runs great (other than the pressure reading and oil leak), not burning just leaking and only for a few minutes as the engine cools. Engine has no noticeable power loss or lack of power even when towing, engine has about 80,000 miles but shows no signs of age other than described above.....

Sorry for the long post, any assistance is greatly appreciated.:confused:

I will check questions as often as I am able...
The low oil pressure is usually related to a bad sending unit on most of the GM's.Have you replaced it ? It is a bit of a bear to get at,down low drivers side,back of engine.Use a GM unit as most of the aftermarket is garbage.A clogged PCV system would cause the rocker cover gaskets to blow out,but you said you replaced the PCV,so hopefully it's working OK.

I don't understand the relation to the oil leaks and low oil pressure,unless it's the obvious and the oil is very low.The rocker cover gaskets are a very good design,and rarely leak much.They are a rubber type gasket that is fully encapsulated in the rocker cover rail,to prevent blowout.If you've gone threw that many,and it's still a problem,you have a serious internal problem that is overpressurizing the crankcase.

I would also have an oil analysis done,as you most likely have a headgasket or intake gasket gone.Either way something is overpressurizing the crankcase and blowing out those gaskets (and the PCV).

I have seen a few vehicles with a blown head gasket,and one with a cracked block,which the oil pressure would start dropping dramatically after a while due to oil contamination from the engine coolant.Funny thing was,you could see no sign of it in the oil,no water droplets,no milky color,nothing.We would change the oil,and all was fine for a bit and the problem would come back over time.

John DiMartino Veteran
I think the sending unit is next to the distributor on the 93's.The 89 and older had them above the oil filter.I may be wrong.Liek Wyldman said,the sending units go bad often.If you really are worried about it,slap a manual guage on there,and get it good and hot ,and see what it is.I doubt it is anything other than the sending unit.Those valve cover gaskets usually last the life of the truck,since they updated them in 86.I havent seen any leak problems with them.You may have a warped cover.Goodl uck


Senior Member
93 chevy oil pressure

I had a 93 K2500 with 350 that exhibited the same dropping oil pressure as the engine warmed up. Replaced the sending unit, also checked with manual gage, same problem occurred. I switched from 5w30 to 10w30, and this helped. I tend to think that these symptoms are of internal wear.

Are your rocker covers blowing out on both sides? Perhaps an oil galley is plugged somewhere?

Keep us posted.

Hope you get it resolved without too much headache or $$.



Senior Member
I will replace the sending unit and update when able to do so. On the oil galley is plugged somewhere? would you have any info on how to check this as well? Someone just the other day had mentioned this, I think it would not hurt to do this as well. I will pray that it's not too serious, I would hope it's just a clog somewhere, engine never looses power or shows the signs of its age so who knows. Thanks again, I will try to update by this weekend... I know the NIEHOFF OIL SENDING UNIT is only like $20, but if you say I need the GM, I will be looking into that as well... Thanks again.

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