Oil Pressure problem

[nightranger302]

have a 02 ranger 3.0 5 speed, Just staring towing a boat and trailer that weigh 3200lbs, after doing a 130 mile round trip to the lake and back, my oil pressure gauge will start to bounce or flicker when the truck comes to an idle. This has done it after towing the boat two sperate trips. It will flicker only two or three times at idle, and then will stay at normal position and not move. any ideas of what be wrong? thanks

 

[Rearanger]

Did you reference you owners manual for max trailer weight. According to my OM 3200 lbs is overweight. Depending on your configeration max weight is about 2500-2600 lbs. You may be overheating the bearing surfaces, especially if route is hilly, and overheating the oil, which will thin it out dropping the pressure.

 

[lorenambrose]

I am new to this forum but I do know Ford puts a resister in the oil pressure circuit to keep the guage steadt. This effectively turns it into an idiot light. I sounds like you very well may have overheated the sending unit, or you have a wiring problem. Can you put a guage in place og the sending unit and check the actual pressure. I would check the easy stuff first.

By the way oil gets THICKER as it heats up till it finally "cokes" up. It thins as it cools until it reaches its base oil cold flow limit then starts to thicken up again.

 

[Rearanger]

By the way oil gets THICKER as it heats up till it finally "cokes" up. It thins as it cools until it reaches its base oil cold flow limit then starts to thicken up again.

Hotter oil will register lower pressure reading as it's resistance to flow is reduced. You'll notice this when looking at a real pressure gauge (not Ford's fake gauge) when starting the vehicle cold where pressure reads about 50psi then drops as oil heats.

http://www.engineersedge.com/lubrication/oil_viscosity.htm

 

[lorenambrose]

Hotter oil will register lower pressure reading as it's resistance to flow is reduced. You'll notice this when looking at a real pressure gauge (not Ford's fake gauge) when starting the vehicle cold where pressure reads about 50psi then drops as oil heats.

http://www.engineersedge.com/lubrication/oil_viscosity.htm

This would be true if you were using a single weight oil. Yes oil thins as it gets hotter, but in milti weight oils, oil is not the only thing in the bottle. As multi weight oil heats up the viscosity modifiers, AKA plastic colis, straighten out and prevent the oil+polimer mixture from thinning below the limit for which it is designed. Multi weight oil is thicker when hot, even though the "oil" part is thinner. If it gets too hot the polimers will form a tar like sludge.that will "coke" up internal parts.

All that being said, he never mentioned the truck overheating so I do not believe he coked up anything. Although an oil analysis will tell for sure.

 

[Rearanger]

Yes oil thins as it gets hotter,... As multi weight oil heats up the viscosity modifiers,

I think we're saying the same thing but understanding the terms differently. Thick/thin is not a good way to convert multi-grade viscosity and the behavior of engineered oil to heat. Oil DOES flow better when hot, hence the less resistance to flow and a lower pressure. As you know pressure is a measurement of resistance, not viscosity. The engine does not have to overheat when the oil gets hotter as the cooling system will compensate for hotter running oil, but I can tell you that putting the engine under greater load will heat the oil more. If he wants to control the oil pressure more when hauling he should add a separate oil cooler, as a trans cooler is recommended for autos. But I suggested he's hauling more than the designed load for the truck which is showing up as hotter/thinner/less flow resistant oil and less oil pressure. Safe braking is another issue. I do agree that using a proper oil pressure gauge will tell a more accurate story

 

[lorenambrose]

I think we are on the same page, just different paragraphs.

 

[Earl43P]

That's an awful lot of verbiage to say, replace the oil pressure switch or find out why the idle is low. Mine has acted like that after sustained high speeds followed by stops at lights. Goose the gas, flicker quits. I wouldn't bother with a pressure gage until I knew the switch was good and the idle is at proper speed.

I don't think anything is wrong, so to speak, but the switch is only ~$20, so it's cheap insurance. You are working it hard, kinda like me towing an Explorer (again) the other day.