Question.
What the hell is going on.. My Oil pressure stays at normal for awhile. I drive around for a bit, and then all of a sudden it goes all crazy like. Goes below normal down the "L" and it seems to do it when the Trans shifts into Overdrive. Now If I get the Trans to downshift the oil pressure goes back to normal.. This is on a 5.8 with ohh low 150k miles on it. hahah

I have changed pcv, oil breather filter, oil to 10w/40 and a shiny new filter.. oh and not to mention the oil pressure sending unit..

So what else could it be.. I do have the change the oil pan on this but its going to have to wait till summer.. Should I also change the main bearings? and oil pump and pickup screen...

Also.. where the hell do I find the coolant temp sending unit, somethings wrong with mine my gauge never moves..

THANKSSSSSSSSSS

 

you should get a mechanical gauge and check the oil pressure to be sure it is ok. My 351 with 150k miles had 6 psi when driving around, I now have 1.5k miles on a remaned engine. The pressure will be higher if the engine is turning faster. If the pressure is low, it's most likely the oil pump or the lower bearings gone.

 

I am thinking its the pump and bearings,, has anyone ever changed those while the motor was still in the truck

 

Hardest part of the job is to get the pan off. Changing bearings and pump isn't that bad. Its a very dirty job. Oil will be dripping on you forever. A word of caution, if any bearings have spun out of position be very careful. If this engine is just old and not any great problems or noises with the lower end, then go for it. Make sure to use a torque wrench.

 

Does the truck run any different? blow smoke? have blow by? High crank case pressure?

I'd bet its a dead sending unit.

 

When the engine isn't warmed up the oil is thicker, which is why the gauge seems fine when you are just starting out. As the engine warms up the oil thins out, and at idle or in overdrive the RPM's are low enough for the gauge to drop down. The sending unit should have helped, but apparently it didn't. It would be best to check the pressure with a mechanical gauge. Changing the oil pump and bearings probably isn't necessary unless the mechanical gauge reads very low. If you want you can just change the pump to give you a boost in pressure to see how it is. If the bearings are worn the new pump won't help much, but you should be hearing excessive noise at startup from the bearings if they are worn.

The coolant temperature sending unit is on the intake manifold near the distributor. It is the single wire sensor lower than the computer coolant temperature sending unit which has more than one wire.

 

I had to change the pcv, and oil breather filter. those were bad so i dont think it has the pressure build up, I am thinking the pump is worn out after the 150k of miles. I have to change the pan, going to wait till summer, I will change the pump and the pickup and possably the main bearings since I will be having an oil bath already..

Thank you all for the help!!!

 

I would go ahead and check the pressure now with a mechanical gauge, you may not have till summer before your valve train chews up.