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Gen 1 new oil pressure sending unit but faint chec

Posted By: so_ber

Gen 1 new oil pressure sending unit but faint chec - 10/31/18 04:49 AM

Hello everyone! I posted this question on another forum but it doesn't seem they are very active so I'd like to give it a shot here.

My first question to my fellow Montero appreciators is in regard to the oil pressure sending unit. The original one was kind of erratic, so the check oil lamp would come on sometimes. After reading many posts here and other forums/the internet it seemed the general consensus was to change it. I got the one for the gauge (as mine is a 1990 LS) and replaced it. I should tell you that when under the car in the limited space, I got a little disoriented so I initially tightened it a bit by accident. Rookie move. Got it off and the new one didn’t want to go on at first. Had to find someone w/ a tap to neaten the threads a little. It finally went in and all seemed well. At night, though, I noticed the oil lamp was still glowing, very faintly. I took my car to a neighbor mechanic and had him check the oil pressure using a gauge. At idle it read around 15 psi, I think. Normal based on the readings others generally get (based on what I've read online). He put the sending unit back on and I’ve been driving it since, and during the day I can’t see any light, but at night, it’s always there. It sometimes gets slightly brighter, but never fully lit, it’s on when the running lights are off. My oil pressure gauge usually reads about 30 psi (or just less), about 15-20 psi idling, and once on a long trip on a warm day it was a little lower (oil heated up?). Anyway, I changed it out about a month or two ago, and it has been the same ever since. Any thoughts?? (Also, I use Pennzoil High Mileage 10W-30, which I've seen recommended online for this rig, but my mechanic just told me it's the worst oil out there...)

This is the one I got, for gauge:
https://shop.advanceautoparts.com/p...h-s933/5972191-P?searchTerm=Oil+pressure
Posted By: Bigshankhank

Re: Gen 1 new oil pressure sending unit but faint chec - 10/31/18 12:39 PM

It sounds like, if your sending unit and gauge are working, you might have some corrosion or a short on the wiring for the warning lamp causing it to glow. Before you replaced the sending unit, when you say the warning lamp would come on, are you saying it would light up fully, day or night, more than just a faint glow?
Posted By: TOASTY

Re: Gen 1 new oil pressure sending unit but faint chec - 10/31/18 03:32 PM

I agree with Hank, it sounds like an electrical issue. I think that light switch is a ground turn on so you maybe have something giving it some ground (possibly the switch internally). This can happen when a sensor is installed in place of a switch, there should be a oil pressure switch and a oil pressure sensor depending on your model Montero. The switch controls the light and the sensor is the sender for the gauge if equipped, it may be a combination switch/sender that does both jobs I don't know because i haven't looked it up for you and my gen 1 wasn't equipped with gauges from the factory so i'm not readily familiar. Do a little research and i think you'll have this sorted in short order.
Posted By: so_ber

Re: Gen 1 new oil pressure sending unit but faint chec - 10/31/18 09:11 PM

Thank you both for your input!

Originally Posted by Bigshankhank
It sounds like, if your sending unit and gauge are working, you might have some corrosion or a short on the wiring for the warning lamp causing it to glow. Before you replaced the sending unit, when you say the warning lamp would come on, are you saying it would light up fully, day or night, more than just a faint glow?


Yes, it would be either completely on or off visible day or night before I changed the sending unit. Now it's really faint, and sometimes, though not often, not on at all. When giving it gas going uphill it often glows a little stronger, but still not near fully on.

Originally Posted by TOASTY
there should be a oil pressure switch and a oil pressure sensor depending on your model Montero. The switch controls the light and the sensor is the sender for the gauge if equipped, it may be a combination switch/sender that does both jobs.


I believe* that the one for the LS does both. For the RS, the switch is the recommended part, and for the LS, the gauge is (and is considered a 'direct replacement'). The one I got is a little bigger than the original OEM one, but it was a little cheaper so I thought I'd try it. I was considering trying the more expensive one next, but wanted to see if people more knowledgeable than me could offer any other suggestions before doing that.

I will check the grounding when I get back. (Of course I start this thread the day I leave on a trip where I'll be gone for a month, haha!)

I will keep you all posted, and any other tips/suggestions are of course welcome as I'm very new to this but excited and eager to learn!

Thanks again!
Posted By: Bigshankhank

Re: Gen 1 new oil pressure sending unit but faint chec - 11/01/18 04:12 PM

Originally Posted by so_ber
Thank you both for your input!

Originally Posted by Bigshankhank
It sounds like, if your sending unit and gauge are working, you might have some corrosion or a short on the wiring for the warning lamp causing it to glow. Before you replaced the sending unit, when you say the warning lamp would come on, are you saying it would light up fully, day or night, more than just a faint glow?


Yes, it would be either completely on or off visible day or night before I changed the sending unit. Now it's really faint, and sometimes, though not often, not on at all. When giving it gas going uphill it often glows a little stronger, but still not near fully on.

Originally Posted by TOASTY
there should be a oil pressure switch and a oil pressure sensor depending on your model Montero. The switch controls the light and the sensor is the sender for the gauge if equipped, it may be a combination switch/sender that does both jobs.


I believe* that the one for the LS does both. For the RS, the switch is the recommended part, and for the LS, the gauge is (and is considered a 'direct replacement'). The one I got is a little bigger than the original OEM one, but it was a little cheaper so I thought I'd try it. I was considering trying the more expensive one next, but wanted to see if people more knowledgeable than me could offer any other suggestions before doing that.

I will check the grounding when I get back. (Of course I start this thread the day I leave on a trip where I'll be gone for a month, haha!)

I will keep you all posted, and any other tips/suggestions are of course welcome as I'm very new to this but excited and eager to learn!

Thanks again!


Yeah, if its growing brighter when the alternator is putting out more juice (higher engine revs), you've got a faulty ground somewhere.
Posted By: GrantCee

Re: Gen 1 new oil pressure sending unit but faint chec - 11/01/18 04:50 PM

Originally Posted by Bigshankhank

Yeah, if its growing brighter when the alternator is putting out more juice (higher engine revs), you've got a faulty ground somewhere.


I wonder if he put teflon thread tape on the sensor when installing. That would do it.
Posted By: so_ber

Re: Gen 1 new oil pressure sending unit but faint chec - 11/03/18 12:32 AM

Originally Posted by Bigshankhank
Yeah, if its growing brighter when the alternator is putting out more juice (higher engine revs), you've got a faulty ground somewhere.


Interesting! That makes sense!

Originally Posted by GrantCee
I wonder if he put teflon thread tape on the sensor when installing. That would do it.


Actually, no, I didn't use teflon tape. I asked the guys at the auto parts store and they said that since it's tapered, it wouldn't be necessary. And since there was no oil leaking after, I figured it was on there snug enough. Are you saying that it could be due to metal-to-metal contact then?
Posted By: GrantCee

Re: Gen 1 new oil pressure sending unit but faint chec - 11/03/18 06:25 PM

Originally Posted by so_ber

Actually, no, I didn't use teflon tape. I asked the guys at the auto parts store and they said that since it's tapered, it wouldn't be necessary. And since there was no oil leaking after, I figured it was on there snug enough. Are you saying that it could be due to metal-to-metal contact then?


No, thread tape could give a faulty ground. You did it correctly.
Posted By: so_ber

Re: Gen 1 new oil pressure sending unit but faint chec - 11/04/18 04:49 AM

Originally Posted by GrantCee

No, thread tape could give a faulty ground. You did it correctly.


Ah, good to know! So somewhere else. I'm pretty new at working on cars and understand some of the basics, but am not skilled in any way. Is there a place that you, Bigshankhank or anyone else suggest checking first? A connection particularly prone to becoming loose or failing? Not sure if it would be related, but my door ajar buzzer sometimes works and stays on as long as the door is open, but other times it starts then cuts off/is intermittent. Everything else seems to work fine (power windows, power locks, interior lights, etc).
Posted By: Bigshankhank

Re: Gen 1 new oil pressure sending unit but faint chec - 11/06/18 02:01 PM

Honestly finding an electrical fault can be daunting and I am afraid I am not the expert in that regard. One thing that I have learned though is that battery cables do not last forever, and when they are decayed they will create all kinds of odd electrical glitches. Thus, when I start trying to sort out electrical problems on older cars I usually start with new cables and then see what problems go away once that's been done.
Posted By: so_ber

Re: Gen 1 new oil pressure sending unit but faint chec - 12/20/18 08:46 PM

Hi again, everyone! Back in town so have a little update. Recently, if I leave my radio on after turning off the engine, the battery drains quickly. I had my battery checked out and it's fine, my alternator charges it fine as well. Anyway, this happened the other night as I was filling up the gas tank. It was on E, and in the time it took to fill, the battery died. They gave me a jump at the station so it was ok. What I noticed, though, was that when I left the station, the Check Oil lamp was off (when I happened to glance at my dash), but as soon as I gave it gas it glowed faintly, but in direct proportion to the amount of gas I was giving it. I would think this would confirm it's a ground issue, right? (Would that also somehow make it so the radio drains the battery drains so quickly?)
Posted By: Bigshankhank

Re: Gen 1 new oil pressure sending unit but faint chec - 12/21/18 03:38 PM

I'm going to reiterate the battery cables again. My daughter's PT Cruiser was killing batteries about every 3-4 months. No warning, it would start fine then the next time she went to start it, no click nothing just completely dead. I finally bought an OEM set of new cables and viola, haven't had that problem in over a year. If nothing else, it's cheap insurance. Not sure if you can get OEM cables for either of the engines for the 1st gens, so you may have to make them yourself or find a shop that can fab new ones using your originals as a template. All this being said, I have yet to take my own advice.
As for the lamp, yes it still sounds like a ground.
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