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Gen 1 new oil pressure sending unit but faint chec #1104658 10/31/18 04:49 AM
Joined: Jun 2018
Posts: 10
so_ber Offline OP
Need a Spot
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

Last edited by so_ber; 10/31/18 05:14 AM.

1990 Montero LS (retrofit project!)
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Re: Gen 1 new oil pressure sending unit but faint chec [Re: so_ber] #1104660 10/31/18 12:39 PM
Joined: Oct 2018
Posts: 79
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Bigshankhank Offline
Getting the Wheeling Fever
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?


1989 Dodge Raider V6
2001 Jeep Wrangler 4.0L
2008 Toyota 4-Runner SR5 4wd
Re: Gen 1 new oil pressure sending unit but faint chec [Re: so_ber] #1104662 10/31/18 03:32 PM
Joined: Jan 2002
Posts: 6,134
TOASTY Offline
Trail Leader
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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.


1999 Montero SAS'd on Kings and stuff

1998 Montero trying to get a V8 Swapped
Re: Gen 1 new oil pressure sending unit but faint chec [Re: TOASTY] #1104664 10/31/18 09:11 PM
Joined: Jun 2018
Posts: 10
so_ber Offline OP
Need a Spot
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!


1990 Montero LS (retrofit project!)
Re: Gen 1 new oil pressure sending unit but faint chec [Re: so_ber] #1104666 11/01/18 04:12 PM
Joined: Oct 2018
Posts: 79
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Bigshankhank Offline
Getting the Wheeling Fever
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.


1989 Dodge Raider V6
2001 Jeep Wrangler 4.0L
2008 Toyota 4-Runner SR5 4wd
Re: Gen 1 new oil pressure sending unit but faint chec [Re: Bigshankhank] #1104667 11/01/18 04:50 PM
Joined: Nov 2013
Posts: 94
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GrantCee Offline
Getting the Wheeling Fever
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.


1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
Re: Gen 1 new oil pressure sending unit but faint chec [Re: GrantCee] #1104668 11/03/18 12:32 AM
Joined: Jun 2018
Posts: 10
so_ber Offline OP
Need a Spot
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?


1990 Montero LS (retrofit project!)
Re: Gen 1 new oil pressure sending unit but faint chec [Re: so_ber] #1104669 11/03/18 06:25 PM
Joined: Nov 2013
Posts: 94
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GrantCee Offline
Getting the Wheeling Fever
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.

Last edited by GrantCee; 11/03/18 06:25 PM.

1987 Montero SWB, 2.6L, 5spd
Weber conversion
2-valve head from Engine Machine Service
"4G54 FTW!"
Re: Gen 1 new oil pressure sending unit but faint chec [Re: GrantCee] #1104670 11/04/18 04:49 AM
Joined: Jun 2018
Posts: 10
so_ber Offline OP
Need a Spot
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).


1990 Montero LS (retrofit project!)
Re: Gen 1 new oil pressure sending unit but faint chec [Re: so_ber] #1104671 11/06/18 02:01 PM
Joined: Oct 2018
Posts: 79
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Bigshankhank Offline
Getting the Wheeling Fever
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.


1989 Dodge Raider V6
2001 Jeep Wrangler 4.0L
2008 Toyota 4-Runner SR5 4wd
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