Whenever I start my truck in cold weather, like 30F or bellow my truck will read no oil pressure on the gauge for a while. After about a minute it will fluctuate, going from normal to zero and back to normal rapidly. Once the truck warms up it reads normal oil pressure. I am sure the truck is getting oil pressure because there are no noises or clunking etc coming from under the hood. I am guessing that the problem is the oil pressure sending unit. What is the procedure for testing them, and could weather cause them to act up, because if it is warmer out I never have this problem. Any extra info on this issue would be very helpful.

 

The fluctuating is usually a sign of a spun bearing, VERY BAD! I suggest that you install a mechanical gage on the engine to get an accurate reading and if the pressure is still fluctuating get ready for an engine problem.

 

It's also possible that your sending unit probe is covered in sludge or having trouble getting a clear read due to some type of restriction until things warm up. Try taking your sending unit out and check the area in the block to see if it's got crud built up around it, restricting clear flow.

 

I wouldn't worry about a bearing. Bad bearings do not typically act up when the engine is cold. The start to grab once the engine warms up and the parts expand. Yes fluctuating pressure could be a sign of a bad bearing but highly unlikely when cold. If the bearing is going bad you will also hear the telltale knock.

I wouldn't bother trying to test a part as cheap as the oil pressure sender, I would simply replace it.

What wieght is the oil? Hopefully you are running the reccomended 5w-20.

 

I am running 5w-50 full synthetic, that shouldn't be causing the problem, I have been running it since I owned the truck and never had a problem with this before. Also there is no knocking from the engine at all, so I will pull out the sending unit and probably replace it.

 

A mechanical gage and kit will cost about the same and give you an accurate reading. The peace of mind of knowing exactly what the oil pressure is would make it worth the invetment, to me, even if it was only used as a test tool and then install the new sending unit.
It's your truck and your money, do what makes you feel comfortable.

 

If you have the extra $50 or so, Mel is correct, a mechanical gauge is a good piece of mind. That said, oil related engine failures are exceedingly rare in anything but badly worn out engines. I have had a bearing go on a fresh rebuild before too but that was an assembly error, not something that just cropped up 100,000 miles into the engines life.

 

High mileage with poor maintenance and occaisionally running too low on oil will bring about a spun bearing.

 

Mel, none of us get every one of these responses right, there is no need to make far reaching statements in order to find redemption.

Actually, high milage with poor maintenance leaves you with larger clearances in the bearings which are less likely to cause one to spin. Low oil is much more likely to create top end wear since the crank and rod bearings are the first to get oil from the pump.

Or was the point that when your engine is completely worn out, you could spin a bearing? That seems so obvious it is hardly worth mentioning, no? Dirtmonkey is a regular contributor here and I do not think his truck is either high milage or neglected.

 

Quote:

Originally Posted by Big Greenie

Mel, none of us get every one of these responses right, there is no need to make far reaching statements in order to find redemption.

I know he is a regular here but his profile information does not indicate if he bought the truck new or what the current mileage is. If I remember correctly.

 

Just to let everybody know, my truck has 88k miles, and it is very well maintained, all fluids are changed at correct service intervals, all fluids are synthetic. So today I will through my oil pressure gauge on it, I already had one, and check the oil pressure. I am probably going to end up replacing the sending unit. Thanks for all the replies.

 

With such low miles and the good maintenance it might just be that the oils is a bit too heavy/thick when the truck is first started in cold weather and just takes a little more time to push through the tiny hole of the sending unit.
Illinois can be bitter cold at this time of year. I used to cover my radiator and battery with cardboard at night as well as covering the engine with an old army blanket if my car had to stay outside overnight when i lived in Chicago and sometimes even put a lamp under the engine's oil pan.

 

I had exact same problem last winter with my 00 Navigator with 130k miles, replace the oil pressure switch ($14.00 at dealer) while i was doing the oil change (in order to reach the switch, you need to remove oil filter first). Since then no problem..and why not to start with cheap and easy stuff...

 

That was my thinking when I saw the 5W-50 oil, even though it is synthetic. (BTW, I use 0W-20 year 'round in my Navi with only 92k on the clock.)

And I agree with moose, its probably the oil pressure - hey - is it a sensor or a switch? (IIRC, years ago Ford would use a switch and as soon as it saw like 5# pressure it would move the gauge to mid-scale - maybe that was on the older Mustangs?)

 

I believe that I have read that it is still the switch type of sensor. That way with even minimal oil pressure the consumers think they are safe from engine failure and there are fewer complaints of low oil pressure for them to deal with.