Hi,

I have a '99 2wd Blazer with 104K. I'm having some strange things occur with my oil pressure gauge andthink my oil pressure sensor may be going bad or I have an oil pump issue.

In the morning when I drive the vehicle to work, its cooler outside and oil pressure appears normal. In the afternoon, when its hotter outside and I'm in more rush hour traffic, the gauge will drop almost to 0 when I'm stopped but then move up to 25-30 when I'm moving.

Does this sound like it could be symptoms of a bad sending unit? I'm thinking that or oil pump. Also, how difficult is it to replace the sending unit?

Any advice would be appreciated.

Thanks,

Rick S.

 

Whenever something like this comes up, I have to recommend that you verify the oil pressure with a mechanical gauge at the sender location. If you see this happening on a mechanical gauge, then you have a problem. If not, then it mostlikely is the sender.

GM specifies that the lowest the oil pressure should go is 6psi at idle. Below that and damage will occur.

Do you hear any noises (tapping, etc) at idle when the gauge drops to around zero? Noises would be an indication of low oil pressure...

 

Thank you for the fast response. Is checking pressure with a mechanical gauge something best left to a shop or is this a part I can buy and do relatively easily myself?

 

It isn't all that difficult to remove the stock sender and install a line to run to a mechanical gauge, but working in the area of the stock sender may be cumbersome. The stock sender is located to the driver's side of the distributor at the back of the engine. You have the fuel lines, the distributor, and the firewall there to really confine the space you have to work in.

Here is an image showing the sender location on an older 4.3L engine. It is all the way in the back (right) on the rear rail between the cylinder heads, pointing towards the top of the photo:

pic courtesy of Tim Hanr (hanr3)

 

Wow, that looks like its going to be pretty tough to get to.Anyone know if youhave to remove the distributor?

 

You will definitely have to remove the cap, but you should be able to get the sender out of there with a wrench after that. It is tight for sure! You'll then need either a length of hose or some additional fittings to put on the manual gauge. You can unscrew the fitting then from the block once the sending unit is out of the way. Then use a 1/4" pipe nipple somewhere around 2-3" long and a 1/4" union into the gauge. Start up the truck and watch the gauge as it warms up.

You'll want to make sure that you use some thread sealer on anything you put in even if only temporary and definitely don't forget the thread sealer when you put everything back together.

*EDIT* - I think it is 1/4" pipe, but now I'm not exactly sure...

 

Thanks for the tips. I may also change the oil/filter. I had the intake manifold gasket replaced a few months ago and they did change the oil, but I think a small chance exists that their could be debris in the filter.

 

UPDATE: Well, as a precaution I changed the oil/filter this afternoon and now the pressure gauge seems to be holding steady. I've been driving it around this afternoon and there is no sign of a problem, so maybe it was a clogged oil filter. There was a lot of crud on the magnetic drain plug.

 

Well that was easy enough it seems! Wasn't a Fram oil filter on there was it?

 

No, it was some no name filter that the shop put on when they did the lower intake manifold gasket. I'm surprised how much crud looked like it was in the oil. A little disheartening to think that was swirling around my motor. Man did they torque the h*** out of the drain plug though[:@] I don't know why they feel its necessary to tighten it down to 100 ft. lbs. Just goes to show you, you gotta do the work yourself to know its done right.

I'm going to drive it tomorrow andmonitor the gauge. Appreciate all your inputSwartlkk.

Rick