I recently bought a 89 1500 with a 305 Truck was in good shape and runs well. But, as the motor heats up it loses oil pressure at idle. When it is cold it is fine. Can anyone help me with this thanks!

 

not an uncommon issue and is normal: as oil heats up it becomes thinner, as motors get more miles on them the bearings get worn and create a "bigger" space for this already thin oil to fill......thus the reduction in oil pressure. Try running 10w30 in it all year. do you loose all oil pressure or does it drop to around 20psi?

 

not sure where is stops dont really lose it all it fills the gauge about a little less then a quarter of it. W/e that would be around. What oil should the truck be using. Being i got it a week ago and been working alot i havent had time really to look what is should be running. Thanks for any help you give!

 

I would use 10w30 in a motor that old. A quarter of the way up the gauge is about 20psi which is about right. A motor that old would probably benefit from a new oil pump. Does it have a 60psi or 80psi gauge in it?......the condition you are describing is normal....I wouldnt worry about it too much unless it has motor noise associated with it.

 

Yes it has the 80psi gauge. Like i said the only thing that really sucks is the idle gets rough when its starts to happen. Other then that it is running perfect. WHat is the reason you would run the 10w 30? That a good oil to be running in an older vechile. Never owned something so old so its all new to me! Thanks

 

yes......like I explained in my first post about the oil and bearing clearances......a rough idle could be several things....I would start by giving it a tune up....i.e. cap, rotor, plugs, air filter, ect....a vac leak can also cause a rough idle

 

I understand that plenty of things could cause a rough idle. Im going to take your advice give it a full tune up and run the 10w 30 in it. And ill report back

 

To check for a vacum leak, get a can of starting fluid and with the truck idling, spray all around the intake in short bursts. If the idle goes up, you can narrow down where the problem is, if its a vacum leak.