Mud_Slinger

I have a 99 4.8. I was running 10w40 royal purple and mine would idle around 55 all the time, cold or warm. When I would get on it, it would run around 75. I started getting a lifter tap so I went to 5w20 castrol full synthetic and it will idle at 40 cold and 35 warm. I say as did a few other people, get a different type of pressure gauge and check it that way.

Mille Racer 69

Hmm, ok - so I think it is apparent that my gauges are inaccurate, I will have them tested.
But can anybody confirm if their gauges read a higher number with the key turned off,
Then when the key is in the accessory/on position but with the engine off as I described earlier?

Thank you everybody for the constructive responses.

OLD WRENCH

As stated before the only way to know what is going on is with a good mechanical gauge. The ones in the truck are not precise instruments. They just give you a rough estimate. 20W50 oil is entirely too heavy for that truck. If you look on your fill cap it should say 5W30. 155 degrees is not high enough for your computer to go into "closed loop" so the engine is running as tho it is cold all the time. You should have a 195 thermo. Ill bet your milage is not too good.

DoubleO7

I just went and looked at my 1999 5.7L
With the key off the volts and fuel stay where they were.
The oil and temp go to zero.
With key on the temp gives a reading if warm enough, but the oil stays at zero.
Since the engine is not running, there is no oil pressure to the sender and the oil gauge is at zero psi.

Running at 155 temps will sludge up your internals, cause poor performance issues, lower mpg, bad emissions, clog your convertor.
Maybe you thermostat is stuck open.

Mille Racer 69

Ya, the gauges are probably FUBAR. I will get the kinks worked out.
To test it I can pour boiling water over the t-stat and the temp gauge should dramatically increase.

No, my gas mileage is not great around town, though it is in the upper teens with the cruise control on
Going about 70 for a long distance.

I will switch to 10/40 oil. 40 weight should be a happy medium.
Since it is a high mileage vehicle I want to use a little thicker weight. Damn, I just changed the oil too.

Aw7233

In my 2001 silverado 1500 with a 5.3 I run 10w-30 valvoline oil and at cold start up pressure is about 50-55 psi. when warm it drops to about 40 and after I've been Driving for an extended period of time and I stop it drops to about 35 psi. But yeah, 20w-50 is way too thickfor that engine.