I would appreciate any help someone can shed for me here. Sometimes when at an idle (stopped), clutch in, my Ranger's oil pressure gauge flickers if I turn on the heat, or if i dont do anything at all. Sometimes it flickers into the red, or jut a little bit to the left. I turn off the engine whenever this happens because I am really scared. I just fixed my head gasket and cracked head because there was ton of coolant in the oil...so I was hoping my bearings aren't shot. But if they were that would cause low oil pressure wouldn't it?

The truck has 175,000 miles so I was wondering if maybe it is just the sender that is shot (i hope!!). If anyone had a similar experience please chime in. Also how hard is it to replace the oil sender...I have the repair manual so I can probably do it.

Thanks!

 

I just went through this with my F150. THe absolute first step is to install a totaly new oil pressure gauge (gauge AND sending unit, aftermarket). This will give you exact oil pressure readings. Im guessing the stock is just an idiot light with a needle?

 

What model year? That is important because you may just have an electical problem in the gauge circuit and not a pressure problem at all. About 1987, Ford stopped using a real oil pressure sender and started using a pressure switch and 20 ohm resistor to "fool" the gauge into reading about half scale at all times there is any oil pressure at all. What may be happening is that your voltage is lower at idle and when you turn on the heater fan, it drops a little more. Clean and tighten the connection at the sender.

The way to tell if you have a real or "fake" sender is to look at it and note how big it is. A real oil pressure sender is over two inches in diameter and height. The pressure switch is less than an inch in both dimensions. A cheap mechanical gauge can be temporarily installed to get a sanity check on your engines oil pressure.

Jim

 

I'm going to say it's probably an electrical problem since the "sender" is just a glorified idiot light. You have 7 PSI of pressure, it reads middle range. Anything below that and it reads far left.

Since yours is reading not middle range but not pegged to the left and it's just a little off, I'm going to say it's probably something with the circuit.

Either way, the first step is to test the oil pressure with a mechanical gauge to see what's really up in cold idle, warm running (2K RPM), and warm idle.

I'm guessing the sender is ok and that the problem is somewhere in the dash wiring, namely the additional voltage required to run the heater, etc. requiring power that causes a slightly hit on the oil pressure gauge, similar to turning on any heavily power laden accessory and therefore everything else suffering. Might be a sign of just a bad battery or alternator as well, get a voltmeter on those to check and be sure.

 

All of the above, plus a good shop, can easily check the oil pressure at idle (fully warmed engine) with a mechanical guage. Takes 30 seconds to hook up. This will give you an accuarate reading, immediately. Engine in gear, under load, ect.

The addition of a mechanical oil pressure guage, (I like Auto Meter guages) and temperature guage, are well worth the minimal cost for the piece of mind they give you.
Ed

 

Agreed...best thing I ever bought for the truck. I kept the old senders and left the wires hanging, so if it comes down to it, I can always just yank the mechanicals and hook the crapola stockers back up. You never realize how bad the stock ones are until you get real ones.

 

I had a 89 ranger and have known others who have had the same problem. I chased it as an electrical problem because it was eratic like that. What I found was that in the late 80's and early 90's Ford made the oil pan gasket to over hang in the oil pan and it deteriorates over time stopping up the pick up screen. That is why when you stop the engine or in some circumstances it will drop to a low pressure and then come back up. You may try a sending unit but I am betting that you need to drop the oil pan and replace the pump, pick up screen and gasket. Two people that I know had their engine lock up because they thought it was electrcal and would get good pressure readings so I would not delay a fix. Its not hard or expensive to do Im betting money on the screen. Just my 2 cents.