305 v6 oil pressure
 

Hi I’m working on a project 61 gmc fleet side with 305 v6 engine on it stars up and the oil pressure is 50 to 60 then after engine warms up at idle the oil pressure goes down to 5 if I rev the engine the oil pressure goes up as I accelerate my concern is at idle is it normal to be that low ?

Re: 305 v6 oil pressure
 

I don't know how accurate this is, but I generally use 10 psi per 1000 rpm as a base line. If idling at 500 rpm with 5 psi then it is OK. If it is idling a 1000 rpm then I would look deeper into the engine. I would drop the oil pan and check the bearing (rod and main) clearances.

This would also depend on the oil you use. A multi-viscosity (like 10W30) then your oil pressure would be lower. A straight weight oil (30W30) would be higher. Also oil that getting close to an oil change would tend to be lower too.

Someone else might have more or better information on this.

Re: 305 v6 oil pressure
 

Greetings, ironage!

5 PSI oil pressure at idle is extremely low. Oil pressure at 50 to 60 PSI with the engine cold should not drop below 35 t0 40 PSI with the engine at normal operating temperature. I would be listening for loose bearings in the engine. Loose Rod bearings will make a clattering noise, while loose main bearings will make a more dull thud like sound. If no loose bearings, it would be wise to check for a stuck relief valve or weak relief valve spring in the oil pump itself. I definitely would not advise you to drive your truck anywhere with only 5 PSI oil pressure at idle with the engine at normal operating temperature. you may find yourself sitting on the side of the road with catastrophic engine (failure) damage.

Re: 305 v6 oil pressure
 

I agree, 5psi is too low. My 66 c1500 runs 60 + cold and never drops below 30.

Re: 305 v6 oil pressure
 

I have a light, which I think is the original system.
It might be a good idea to verify and/or calibrate your gauge.

Re: 305 v6 oil pressure
 

Gage was added to my truck as well

Re: 305 v6 oil pressure
 

if you were talking about a wet-sleeve diesel engine, i'd say that you had cut the camshaft bearings out of the engine due to anitfreeze in the oil changing it into a cutting compound. The oil pressure is built on the camshaft bearings in most gasoline engines. the easiest way to find the problem is to drop the oil pan, take a pressurized container with the test lube(50% virgin oil +50% K1 kerosene) and attach the hose to the fitting that you screwed in place of the sending unit and pressurize the canister. with the canister pressurized, look up inside the crankcase of the engine. where you find a spill comparable to Niagra
Falls you will find your leakage in the oil system.

Re: 305 v6 oil pressure
 

Thanks to all for the inf shared I flushed the oil clean the canister and put a new oil filter added 15w-40 that it will be flush again after that if it does not get better I will change the oil pump IMG_0845 is better but not satisfied yet

Re: 305 v6 oil pressure
 

IMG_0845.PNG that the reading on my gauge