98 gmc

backwoodsblonde · February 13, 2013

I have a 98 GMC sierra with the 5.7L and every time I drive it, my oil pressure is all over the place. When its started cold it reads 60, when its warmed up at cruising speeds of about 55-60mph it reads 40, but as soon as the RPMs drop when I coast, idle, or drive under about 10-15mph (warmed up) the pressure reads 20.

Is this normal.. Sure doesnt seem right to me. I had a bonneville a while back and the oil pressure never varied like this.

KMGZ400 · February 13, 2013

the gauges are probably shot, my GMT400 did that too

kstruckcountry · February 13, 2013

It's normal for it to be higher when it's just been started, but I don't think they usually drop that much when idling.

IMO the best thing to do is buy an aftermarket gauge pod, like this: http://www.summitracing.com/parts/equ-8100/overview/

I had one in my 1990, and it worked great.

Badass69 · February 15, 2013

Sounds pretty normal to me. Oil pressure varies with engine rpm greatly. If it doesn't that means you have a gauge that doesn't work or it's really just a feel good idiot light.

20 psi at low rpm, 40 at cruise and 60 cold sounds pretty damn normal for almost every Vortec 262/305/350 I have ever driven with any kind of miles on it.

waumo1 · February 15, 2013

Yes that is exactly the way my 98 5.7L behaved. I used the recommended 5W-30 oil.

backwoodsblonde · February 18, 2013

thanks you guys!

1997SierraSLT · April 25, 2013

My 97 GMC Sierra K1500 has 150,000 on the odometer. I bought it at 17,000 miles it has shown about 20 psi at idle, a little below 40 psi at freeway driving speed, and around 60 psi at cold start from day one. I believe this is completely normal with these trucks. I've been using 10W-40 Castrol motor oil.

Steve