I have a question about my '69 Mach 1 and was wondering if anyone has had the same thing happen. My low oil pressure light keeps coming on when my car is in gear, warmed up to running temperture and idling. When I hit the gas and increase the rpm's the light goes off. The car seems to run just fine when the light is on and I do not hear any ticking from inside the engine to make me think that there is something wrong internally. The light does not come on when the engine is cold. Are these cars notorious for doing this or do I have a bad sensor, or something worse?

 

well the sensor sounds to be working right. when the car is cold the oil is thick and pressure is higher. When its hot the oil is thinner and gives less pressure. Hence no problem when cold only when hot.

2 things, whats the idle set at and what weight oil are you using? i think one of the two is a problem.

Oh and whats the motors deal, stock from ford or rebuilt?

 

I'll venture a guess and predict that the motor has quite a few miles on it and/or is original. In any case, oils used to be thicker, single weight, and clearances bigger. All of those things can contribute to low oil pressure.

Start by making sure your oil pump isn't all caked up inside with gunk, then make sure you keep a decent weight oil in it unless you've had it built/rebuilt with tight clearances. Once you've got all that sorted out, if it's still doing it then try a bottle of STP (blue bottle) oil treatment. It's a viscosity index improver and will thicken the oil quite a bit. It helps with tapping lifters and low oil pressure.

Straight 30, 20w/50, 10w/40 are all good options. It's winter so you'll have to make the call on which one based on temperatures in your area.

 

Thanks for the replies so far. The engine is not original to the car so I am not exactly sure how many miles are on it. It is a 351 4v windsor and I would guess that it has quite a few miles on it even though it runs strong. I was thinking about going to a heavier weight oil since I only have 10w-30 in it right now hoping that that would solve my problems but just wanted some other opinions. Thanks again for the help!

 

Sounds like a engine with high miles then if its getting low oil pressure with 10w-30. Like my man red said jump up to 10w-40 next change with higher mileage motors you need to step up the weight of the oil as the motor gets more wear.

 

The car is also idling a little slow while in gear which is not helping the situation. I'll step up the oil weight and adjust the carburetor and see what that does. Thank you again for the help.

 

You should just sell me the mach, it's just not worth fixing it