Fix + Fast
This repair was done on a V6-powered minivan, but most cars will have a similar process.
by Pete Jackson. Also see the main minivan repairs section.
Bob Lincoln wrote: “All of these oil sensors drift low in their readings as they age. They are piezoresistive wafers, that is, they are a strain gauge, essentially a Wheatstone bridge. Their resistance changes with deflection. The more they are used, the more the wafer is mechanically worked until the resistance changes and conducts more current to ground, thereby lowering the gauge reading. It's a well-known aging effect.” Several readers have reported issues with aftermarket gauges failing shortly after installation.
When the wife returned home from work last night she mentioned the oil pressure gauge had an erratic display. I know the sending unit has been on its way out, so I guess it was time.
You would sit at idle and the pressure would drop almost to the point where the check gauge light would come on and while driving the gauge would alternate between high and low. It never did go low enough to trigger the light, but it was still an eye opener.
So today I changed the sending unit, along with the brake light switch (to cure lights that intermittently stay on).
To change the oil pressure sender (If you have done an oil change, this is very similar):
1) Raise and safely support the front of the vehicle.
I use a pair of ramps when I lift mine, unless a wheel/tire needs to come off.
2) While the exhaust manifold cools, grab your tools, you will need:
3 ) Slide under the front of the van by the right front tire and look straight up, you will see the oil filter and next to it about 2 inches away, the oil pressure sender (it has a two prong plug).
4 ) Position the drain pan and open the oil drain plug to drain the oil. Then move the drain pan under the oil filter. Remove the oil filter (using a filter wrench if you have one) to gain clearance to swing the ratchet when removing the sender. You could also change the sender using an extension to clear it. My 1/2" drive extension was far too long to be of use.
5 ) Unplug the oil pressure sender and using the 1 1/16" DEEP socket on the 1/2" drive ratchet, unscrew the sending unit from the cylinder block.
6 ) Wrap the threads of the new sending unit with Teflon tape to prevent leaks and screw in the new sender.
7 ) Using the socket and ratchet, tighten the O.P sender in firmly. KOG wrote that this should be torqued to 60 inch-pounds, but he also wrote, “Do not use teflon tape on the sending unit. Use a paste thread compound such as Teflon T+2. Teflon tape can prevent the sending unit from grounding to the block reliably, resulting in erratic readings. You don't have to ask how I know this.”
8 ) Plug the sender back in.
9 ) Install the new oil filter, making sure to lube the gasket with clean engine oil. Also make sure the old gasket isn't stuck the oil filter-mounting surface.
10 ) Start the vehicle and check for leaks and watch the oil pressure gauge rise. At this point you will be about a quart low, but you will refill it here soon.
11 ) If no leaks are present, lower the vehicle to the ground.
12 ) Check oil level and add as necessary.
Now enjoy a pressure gauge that gives you an accurate (well, as good as it gets) reading.
It would also be a great time to change the oil while you did this, you already have the oil change tools handy, and you have oil handy, so why not do a little preventive maintenance while you are at it?
This entire repair took about ten minutes, or about the length of oil change....
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