Oil gauge stuck at full

Hi Guys and Gals,

I have a '97 Blazer 4.3L engine. I had a mechanic replace the "oil pressure sending unit." Now the guage is stuck at the maximum pressure position. It is like this when the engine is both on and off. When you turn on the engine, it twitches slightly for a moment. There are no "check gauges" lights on the dash.

Anyone have ideas why this is happening? Here are some possibilities I was thinking of:
1) The electrical connector is not snug and is not making full contact, like it wasn't plugged into the back of the sending unit at all.

2) The mechanic didn't disconnect the battery and a spark caused damage to the sending unit when he connected it.

3) The sending unit is defective (but it is a new part)

4) I need to drain the oil and refill it... like there is excess pressure built up or something.

This all came about because the oil pressure gauge was erratic and often dropped to zero when let off the gas. The "Check guages" light would turn on. I read the other threads here that suggested the "oil pressure sending unit" is the most likely problem.

I wanted to replace the sending unit myself, but found it to be a bit hard. It was located under the distributor. I was afraid to disconnect the distributor to get to it so I took the part to a mechanic to replace.

If the electrical connector is disconnected from the oil sending unit, does it read full or empty? Does it show an error on the dash board?

Any and all advice appreciated.

Hi Guys and Gals,

1) The electrical connector is not snug and is not making full contact, like it wasn't plugged into the back of the sending unit at all.

3) The sending unit is defective (but it is a new part)

If the electrical connector is disconnected from the oil sending unit, does it read full or empty? Does it show an error on the dash board?

Any and all advice appreciated.

Usually when there's no connection, the gauge will shoot up past the top reading. Either #1 or #3 is your problem. You should be able to see if the connector is on the sending unit .

take it back to him and demand he checks it out it should have not left the shop if it was not working

Thank you Mike and Redwheeler. I wasn't there, my wife took the truck in for servicing during the day. By the time he had replaced the oil sending unit she had to leave the shop anyway to pick up our daughter from school.

The mechanic assured me that he plugged it in nice and snug. I'll purchase another $20 sending unit and ask him to install, must have been a bad one. I'll try to return the defective one to Advance Auto.

The saga continues. We took our Blazer back and had our mechanic put in a 2nd oil sending unit. Now the the gauge is giving wildly swinging readings. Sometimes it is around 45 and other times it is at zero (and the "check gauges" light turns on). It jumps around between 45 and zero mostly at idle or when the accelerator is kept in a constant position.

This current behavior is what the original oil sender was doing which was the reason for trying to replace it.

I kinda want to give up and ignore the gauge reading and just watchout for when it stays at zero or the engine temperature starts to go high as a warning sign that I've lost oil. Is it possible that there is some other larger problem and that the oil sender unit is actually working correctly?

Thanks for any advice and tips you guys have. You all are the best! Whenever I've had a problem with our Blazers, there is always someone with more insight than me who lends a helping hand on these forums. Thanks in advance.

You need to have a manual gauge put on there to see what your true oil pressure is. There must be something wrong because what are the chances of three bad sending units.

This might be a 1997 ignition switch problem.

I'd say the first time the mechanic used an oil pressure switch, not sending unit, which is meant to turn a dummy light off and on. This would explain the pegged guage. Now that the right unit has been installed, it has uncovered your original problem. I agree on hooking up a manual guage to verify proper pressure. If it's good, start looking for wiring/electrical problems..

Thanks for everyone's replies. I didn't see most of them till now because, for some reason, I wasn't getting email notifications.

I found the problem after all this time! Turns out that I needed to drain the oil and refill it, problem solved! I discovered this when I changed my synthetic oil (do it once a year or every 25,000 miles).

The erratic reading and "check gauges light" eventually became nearly stuck at no pressure and then the "check gauges light" became constant. Changing the oil solved the problem. The Hanes (or Chilton's) manual said you are supposed to remove the oil and then put it back... now I know why. I guess it releases some pressure or restabilizes somehow. Probably the first gauge wasn't faulty either.

-- Aaron

That still seems very odd that a drain and fill fixed this. I would watch it

Thanks for everyone's replies. I didn't see most of them till now because, for some reason, I wasn't getting email notifications.

I found the problem after all this time! Turns out that I needed to drain the oil and refill it, problem solved! I discovered this when I changed my synthetic oil (do it once a year or every 25,000 miles).

The erratic reading and "check gauges light" eventually became nearly stuck at no pressure and then the "check gauges light" became constant. Changing the oil solved the problem. The Hanes (or Chilton's) manual said you are supposed to remove the oil and then put it back... now I know why. I guess it releases some pressure or restabilizes somehow. Probably the first gauge wasn't faulty either.

-- Aaron

That Make's sense now, Your OIL filter was PLUGGED UP...
25 THOUSAND MILE OIL CHANGES have the tendencey to do that...

That Make's sense now, Your OIL filter was PLUGGED UP...
25 THOUSAND MILE OIL CHANGES have the tendencey to do that...


Or it was out of oil period:disappoin ....hope the engine bearings are OK, ya gotta pull the ol' dipstick every now and then.

Thanks guys. No, it hadn't lost any oil. Also, the engine temp was always very low. Very curious thing.

Recurve,
Do you run your oil filters 1 year or 25,ooo miles and then change them with the oil? Also what brand of oil filter do you use?

. . . and just watchout for when it stays at zero or the engine temperature starts to go high as a warning sign that I've lost oil. . . .
If you depend on the engine temp as a sign that you have no oil pressure, you'll be replacing a lot of engines.

I use AMSOIL brand for the oil and the filters. I had been using their 6 month filters, and when I changed them, I'd add one quart of oil. At the 12 month interval I'd change the filter and do a complete oil change.

Now AMSOIL has changed their filters and they are supposed to be good for 1 year or 25,000 miles. I just installed one of these newer filters for the first time when I did the oil change.