# Car oil pressure question **URL:** \ **Category:** Factual Questions\ **Created:** [February 2, 2014, 4:02pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353 "2014-02-02T16:02:38Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 2, 2014, 4:02pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/1 "2014-02-02T16:02:38Z")
2002 Jeep Grand v8. My Wifes car. The vehicals oil pressure gage is reading high. About 3/4 instead of the usuall 1/4 (the position of the needle on the gage). It does not matter if the engine is cold or hot. The oil level is not low. The engine temp gage does not show it is running hot. Engine RPM does not seem to make a differnce to what shows on the gage. Hmmmm…Gage/sensor bad? Oil pump gonig bad? Perhaps a bad oil line, causing the pump to overwork? We are going to have this looked at ASAP, but I wonder what may be causing this. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [February 2, 2014, 4:22pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/2 "2014-02-02T16:22:06Z")
So the gauge shows pretty much the same reading from idle to high revs, hot or cold, regardless? What does it show when the electricals are on (second key position, “Run”) but the engine is off? Based on your description, I’d say bad sender. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 2, 2014, 4:54pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/3 "2014-02-02T16:54:10Z")
Yep, the gage shows the same reading at any RPM. Good idea to check the gage at key #2 position. I don’t think I checked that. I won’t be able to check it for that until my Wife gets home. About 4 hours from now. No engine light is on and the car is running fine. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [February 2, 2014, 4:58pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/4 "2014-02-02T16:58:26Z")
This is why people serious about their engines run mechanical oil and temp gauges. :dubious: I just replaced an electrical oil sensor on my daughter’s Subaru that was not only showing scary oil pressure warnings but leaking like an SOB to boot. There is no place for wires or bakelite in critical mechanical systems… ---
**Author:** ![JerrySTL](https://avatars.discourse-cdn.com/v4/letter/j/e274bd/32.png) [@JerrySTL](https://boards.straightdope.com/u/JerrySTL)\ **Post date:** [February 2, 2014, 5:01pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/5 "2014-02-02T17:01:18Z")
High oil pressure is seldom a problem. The engine has a pressure relief valve after the oil pump to dump off excess pressure. Decades ago, around 1980, I saw one of these pressure relief valves stick closed and the oil filter would burst open! Have you changed the oil recently? It’s possible that the wrong oil was put in. Something like a 20W-50 instead of a 10W-30. About the only other mechanical possibility is that something has clogged an oil passage and the relief valve relieves pressure at a point that the pressure gauge is reading high. However I’m bettign that it’s 98% sure to be an indicator problem. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [February 2, 2014, 5:01pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/6 "2014-02-02T17:01:57Z")
maybe change the oil filter and see if it is still high. maybe disconnect and reconnect the sensor a few times cleaning the connections. then next maybe a bad sensor. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [February 3, 2014, 1:38am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/7 "2014-02-03T01:38:45Z")
[http://www.rockauto.com/getimage/getimage.php?imagekey=4589238&imageurl=http%3A//www.rockauto.com/info/Airtex/1N2.jpg](http://www.rockauto.com/getimage/getimage.php?imagekey=4589238&imageurl=http%3A//www.rockauto.com/info/Airtex/1N2.jpg) Looks like your Jeep has a switch instead of a pressure sensor. What looks like a gauge is really just an Idiot light in disguise. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 3, 2014, 3:30am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/8 "2014-02-03T03:30:05Z")
Terminology time: In the automotive realm, sensor is used to denote a device that gives input to the computer. A device that gives input to a gauge or warning light is called a sender, sending unit, or (usually only for a light) a switch. > [@Gbro](#): > > [http://www.rockauto.com/getimage/getimage.php?imagekey=4589238&imageurl=http%3A//www.rockauto.com/info/Airtex/1N2.jpg](http://www.rockauto.com/getimage/getimage.php?imagekey=4589238&imageurl=http%3A//www.rockauto.com/info/Airtex/1N2.jpg) > > Looks like your Jeep has a switch instead of a pressure sensor. > What looks like a gauge is really just an Idiot light in disguise. No, there’s no such thing as a gauge that is really “just an Idiot light in disguise.” If it has a gauge, it gets variable input and displays variable readings. I can’t see from your linked photo what Rock Auto calls this part, but if they call it a switch the conclusion to be drawn is not that the vehicle doesn’t really have a gauge, but that Rock Auto is not careful with their word choice. ---
**Author:** ![48Willys](https://avatars.discourse-cdn.com/v4/letter/4/db5fbb/32.png) [@48Willys](https://boards.straightdope.com/u/48Willys)\ **Post date:** [February 3, 2014, 7:27am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/9 "2014-02-03T07:27:45Z")
> [@JerrySTL](#): > > High oil pressure is seldom a problem. The engine has a pressure relief valve after the oil pump to dump off excess pressure. Decades ago, around 1980, I saw one of these pressure relief valves stick closed and the oil filter would burst open! > > Have you changed the oil recently? It’s possible that the wrong oil was put in. Something like a 20W-50 instead of a 10W-30. > > About the only other mechanical possibility is that something has clogged an oil passage and the relief valve relieves pressure at a point that the pressure gauge is reading high. > > However I’m bettign that it’s 98% sure to be an indicator problem. I concur that it is probably an indicator problem. Look at it first along with its wiring. Anther things that can cause this is stuck pressure relief valve. With the gauge staying steady at all RPMs, I would look at the pressure relief valve second. Remove and clean it. Reinstall and test drive the Jeep. The last thing, a plugged oil passage, is very bad! It is also very rare. The only time I found this was on an aircraft engine. The pilot asked us about having higher then normal oil pressure. We drained his oil and found metal filings in it (both aluminum and copper)! When we tore the engine down, we found that the engine case had cracked. This caused the #3 bearing saddle (where the #3 main bearing goes) to break free of the main case. It shifted forward and became offset from the oil supply line, partially cutting off the oil supply to one main bearing and two rod bearings, as well as one piston cooling nozzle. The aluminum was from the crank case and the copper was from the bearings. I hope that this is not your problem! I doubt that it is. IHTH, 48. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [February 3, 2014, 1:43pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/10 "2014-02-03T13:43:43Z")
I checked with the engine off and the key on and it still showed about 3/4 high. I then started the car and it was at about the same place. When I rev the engine a bit it goes a little higher. So, it does sound like a sensor/sending unit. We are having it looked at next weekend. My days of working on cars (at least new cars) are over. Thanks all enipla ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [February 3, 2014, 3:32pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/11 "2014-02-03T15:32:22Z")
> [@enipla](#): > > I checked with the engine off and the key on and it still showed about 3/4 high. I then started the car and it was at about the same place. When I rev the engine a bit it goes a little higher. So, it does sound like a sensor/sending unit. The remaining case would be if the gauge stayed at that position even with the key off, which would mean the gauge itself was broken. But yes, this “stuck at one position whenever power is on” indicates a bad sender. > [@](#): > > We are having it looked at next weekend. My days of working on cars (at least new cars) are over. Good call, then. I was lucky in that Subaru oil pressure senders are at the top front of the engine; swing the alternator out of the way and you can all but change it with your fingers. Most senders are in a dark, dirty armpit of the engine assembly and best left to those with lifts, a lot of tools and a liking for poking in dirty pits. ---
**Author:** ![Amateur\_Barbarian](https://avatars.discourse-cdn.com/v4/letter/a/59ef9b/32.png) [@Amateur\_Barbarian](https://boards.straightdope.com/u/Amateur_Barbarian)\ **Post date:** [February 3, 2014, 3:38pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/12 "2014-02-03T15:38:26Z")
> [@Gary\_T](#): > > No, there’s no such thing as a gauge that is really “just an Idiot light in disguise.” If it has a gauge, it gets variable input and displays variable readings. Sorry, but not true. It used to be that you had an ijjit light, triggered by a simple sensor of some kind (off=good, on=pick up a new engine at AutoZone, fool), or a gauge, driven by some analog sender that moved the needle in some proportional manner to whatever it was analoguing. Many newer cars have a half-assed hybrid - it looks like a gauge, adding kewl sportiness and cachet, but does not function like a gauge, which might confuse drivers who aren’t even quite sure what a tach displays. These oil pressure and coolant temp “gauges” are just two- or three-stage idiot [del]lights[/del] indicators that can only point to “off,” “low,” “normal” and “high.” Sometimes just “normal” and “bad.” The sender doesn’t send an analog signal; it, or the ECU, sends one of two or three fixed settings. ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [February 3, 2014, 8:18pm UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/13 "2014-02-03T20:18:44Z")
Thanks AB, Gary, Take a look at a 1999 Dodge Ram 1500 318cid I am still driving this old half dead pickup every day and it has over 300K on it. I have/need to add a quart of oil at every refueling. If I don’t have my synthetic oil I will not add the needed oil, then as has happened a few times, I have run it down low enough that when I come to a stop my Idiot (Me) gauge in disguise will drop to zero and a gauges light will lite and the same chime that sounds for low fuel level will sound, then as the truck settles into the stop or stops deceleration the light goes out and the indicater needle in the make believe gauge jumps back into mid swing position. Of course when this happens I get any 10-30 10-40 oil on sale and carry on. When I entered the information into Rock Auto that the OP provided the listings for oil pressure sender for gauge listed it as a switch. And the picture I linked is a switch, IMO :dubious: ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 4, 2014, 5:37am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/14 "2014-02-04T05:37:26Z")
> [@Gbro](#): > > Looks like your Jeep has a switch instead of a pressure sensor. > What looks like a gauge is really just an Idiot light in disguise. > [@Gary\_T](#): > > No, there’s no such thing as a gauge that is really “just an Idiot light in disguise.” If it has a gauge, it gets variable input and displays variable readings. > [@Amateur\_Barbarian](#): > > Sorry, but not true. It used to be that you had an ijjit light, triggered by a simple sensor of some kind (off=good, on=pick up a new engine at AutoZone, fool), or a gauge, driven by some analog sender that moved the needle in some proportional manner to whatever it was analoguing. > > Many newer cars have a half-assed hybrid - it looks like a gauge, adding kewl sportiness and cachet, but does not function like a gauge, which might confuse drivers who aren’t even quite sure what a tach displays. These oil pressure and coolant temp “gauges” are just two- or three-stage idiot [del]lights[/del] indicators that can only point to “off,” “low,” “normal” and “high.” Sometimes just “normal” and “bad.” The sender doesn’t send an analog signal; it, or the ECU, sends one of two or three fixed settings. My, what delicious crow I’m eating. :o Apparently you gents know something I wasn’t aware of. It’s a bit embarrassing, since I make my living fixing cars, but I guess you can’t know everything. This is a feature I haven’t run across yet, so I’ve learned something. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [February 4, 2014, 5:44am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/15 "2014-02-04T05:44:48Z")
> [@Gary\_T](#): > > Terminology time: In the automotive realm, sensor is used to denote a device that gives input to the computer. A device that gives input to a gauge or warning light is called a sender, sending unit, or (usually only for a light) a switch. > > I can’t see from your linked photo what Rock Auto calls this part, but if they call it a switch…Rock Auto is not careful with their word choice. > [@Gbro](#): > > When I entered the information into Rock Auto that the OP provided the listings for oil pressure sender for gauge listed it as a switch. > And the picture I linked is a switch, IMO :dubious: What I wrote above is what I came to understand from dealing with this for decades, but… My professional repair info calls it a sender on one page and a sensor on another page. One of my parts sources calls it a sending unit in one brand and a switch in other brands. :smack::smack::smack: On this vehicle it’s a three-wire sensor that send input to the computer, which then sends a signal to the gauge. I wouldn’t call it a switch, but they didn’t ask me. 😉 ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [February 6, 2014, 3:55am UTC](https://boards.straightdope.com/t/car-oil-pressure-question/680353/16 "2014-02-06T03:55:00Z")
Way back in the 70’s i had an F100 Ford 4x4 and i thought the engine oil gauge was a dummy system until i found there was a module l of some kind on the back side of the dash cluster that was B.O. after replacing that item my oil pressure gauge would raise and fall with engine speed and temp changes. Not so with my old Dodge, but my new Chevy has a nice sensitive fully functioning gauge. One thing on the old Dodge, when i run low of oil and the indicator drops to “0” i have never heard the unmistakable sound of low oil pressure. The sound of lifters loosing pressure. So i must still have over 15 psi when the switch drops out. And at one time years ago i had a problem lifter that was clicking away. JB had a product that cleared that up and noise never returned.