MI_Mitsu
Rock Warrior
Reged: 03/24/06
Posts: 702
Loc: Romulus, Michigan (Detroit)
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Subject truck is my 91RS with the 3.0L/Auto. Now first let me begin by saying I'm fully aware of the pitfalls of electric oil pressure gauges in general - especially the OE Mitsu units - and the benfits of going mechanical. I'll prehaps one day get there, but for now this is what I have. Well this and a $20 oil pressure gauge tester from Harbor Freight.
When I first bought this truck about 13 months ago, all I had was the idiot light. I then installed the tripod assembly, switched the pressure sender to a unit for gauge and removed the light bulb from the dashboard as required. But my intial readings I got were a little disappointing - hardly anything at all - maybe 5 lbs/in2.
Next step was getting the harbor freight tester unit. Unscrewed the new oil pressure sender I got to use with the gauge - installed the tester and tester shows avg 15lbs/in2. Shrugged it off as gauge in the tripod assy as being out of tolerance and let it go until a month ago.
After 1 30min expressway run that shes not used to, I could hear the lifters or maybe the VLA's tapping away. Checked the oil and of course barely registering. Should have known better with a bum gauge.
Added a bottle of CD2 engine cleaner PLUS 2 more qts of 10w30.
Thing is now - I get a reading on the factory gauge. A good reading from what I can tell... about 32-33 lbs/in2. Inititally only on startup. After idle smooths and the truck runs a few miles, the oil pressure gradually drops to 20lbs/in2 Then after about 10-15 miles, the gauge at idle/stops is barely showing 5lbs/in2. On acceleration it'll get back up to maybe 15lbs/in2 - but nowhere near the high pressure I see at startup.
I know I need to do a full complete engine flush. But what would cause good high pressure only on startup? Only thing I can think of is migrating sludge, but as the engine gets warmer, the oil should become easier to pump and flow - right?
Anyone else see wild fluctuation of oil pressure during a single trip like this?
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89 Montero LS 3.0L/Auto
91 Montero RS 3.0L/Auto
87 Dodge Raider 2.6L/Auto
90 MightyMax 2.4L/Man
Parted/gone - parts available!
89 Montero LS 3.0L/Auto [Blue/Blue] (identical to my 1st), 88 Conquest SHP
Others: 37 Lincoln
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FrankR
Web Wheeler
Reged: 02/01/04
Posts: 10225
Loc: Columbia, SC
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Quote:
I know I need to do a full complete engine flush. But what would cause good high pressure only on startup?
The oil is cold and therefore thicker at startup. As a result, it doesn't flow as well.
Frank
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'89 G-Raider Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 155k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, 165A alt., Lifeline AGM, Rust-Oleum
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MI_Mitsu
Rock Warrior
Reged: 03/24/06
Posts: 702
Loc: Romulus, Michigan (Detroit)
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Just at lunch and let it run while I ate in the truck due to battery issues (see other thread) and again sitting there at idle the needle was practically resting on zero. revved it up to 2000rpm and I maybe got 3lbs/in2 out of the gauge.
On the drive back, I dont think it ever got up over 10lbs of pressure.
Should I go thicker like a 10-40 or even 20-50 to keep the oil pressure up? The consequence i know can be that the VLA's wont get enough oil.
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Dylan
Mudrunner
Reged: 12/15/09
Posts: 291
Loc: Peoria, AZ
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Ironic that this was posted as I have noticed some weird things over the last two weeks with my oil pressure gauge after it was rather predictable originally. I wrote it off to the gauge and/or sender just not being reliable as you stated, but now you have me worried.
In my case though, it often seems to be the opposite. I hadn't driven the truck for a couple days, but my wife had. First time I drove it, I noticed the "near zero" status of the gauge immediately. She said "it's been like that all week and I forgot to tell you." 5 miles down the road, I hit a larger bump and the pressure jumped up to 20 or 30lbs (where it often was before). Since then, sometimes it registers near 0 (usually at startup) or sometimes it registers over 15 but never more than 40. Before the funny behavior, it used to be at about 45 or so when cold, and drop to about 25 when running at 40mph after warming. RPM would affect it a little up or down, as would how hard the engine was working, so I assume that's something close to normal. But this reversal (higher pressure after warming, if it reads at all) is strange to say the least.
Not sure that helps you any, except to say my gut says we are in a similar boat even though mine is a 3.5L. I am very interested to see if you can find an answer because I sure can't. My oil is clean, I have changed it twice in the 3500 miles I have owned the truck and I ran Sea Foam through on one of those oil changes. Looks good, level is good, filter is new, the valves don't make a single sound... mine is so quiet that several other Monty owners on a recent run were commenting on it. Are MI and I both just chasing ghosts?
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'95 Montero SR 3.5L, Trail Gear Sliders, Rugged Ridge XHD Front Bumper, 33x12.5 Duratracs, much more in the works....
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FrankR
Web Wheeler
Reged: 02/01/04
Posts: 10225
Loc: Columbia, SC
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It's hard to diagnose anything in the area of engine oil pressure with the OE gauge unit. You might want to buy a new sender and/or swap in a good used replacement gauge head. You may have damaged the gauge with the alternater/battery issues.
If the lifters are tapping, it may be that you have good oil pressure, but collapsed lifters - so the best thing would be to replace the lifters.
I don't like the idea of heavier oil than 10W-30 for a Gen1 3.0L, but with sumnmer coming up, you could probably go a little heavier without causing trouble.
Is the engine temperature ok?
How many miles are on the engine?
Frank
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'89 G-Raider Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 155k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, 165A alt., Lifeline AGM, Rust-Oleum
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Frumious
Wheeler
Reged: 05/22/09
Posts: 128
Loc: Anchorage, Alaska
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Quote:
Thing is now - I get a reading on the factory gauge. A good reading from what I can tell... about 32-33 lbs/in2. Inititally only on startup. After idle smooths and the truck runs a few miles, the oil pressure gradually drops to 20lbs/in2 Then after about 10-15 miles, the gauge at idle/stops is barely showing 5lbs/in2. On acceleration it'll get back up to maybe 15lbs/in2 - but nowhere near the high pressure I see at startup.
..... what would cause good high pressure only on startup? .....t as the engine gets warmer, the oil should become easier to pump and flow - right?
Anyone else see wild fluctuation of oil pressure during a single trip like this?
You and I have the same vehicle. We also had the same oil readings under the same driving conditions. When cold, the oil is thick and the pressure is high. When hot, the oil thins and the pressure drops. My pressure ranged in exactly the same ranges as yours.
Wanting the pressure to be a bit higher when cruising at highway speeds (20+ desired), I added Lucas Oil Stabilizer which has the effect of keeping the oil a bit thicker and keeping it up in the heads. It worked. I mix it at a ratio of 1 part Lucas to 4 parts regular oil.
The engine is much quieter now.
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1993 Montero SR 4dr V-6 3.0L Auto "Thunder" (in Alaska)
1960 Bentley S2 V-8 6.3L Right Hand Drive
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MI_Mitsu
Rock Warrior
Reged: 03/24/06
Posts: 702
Loc: Romulus, Michigan (Detroit)
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Quote:
It's hard to diagnose anything in the area of engine oil pressure with the OE gauge unit. You might want to buy a new sender and/or swap in a good used replacement gauge head. You may have damaged the gauge with the alternater/battery issues.
Thought I mentioned this above: original set-up was with an idiot light. When I added the gauge tripod assy, I installed a new proper oil press sender for use w/gauge. Standard brand.
As for the damaged gauge idea - this was my first thought last year. Until I added the nearly 3 qts of oil and I started getting good pressure readings, but only with a cold start, and only for the first 5min or so. But you're right I should try another gauge, maybe Autometer brand.
Quote:
If the lifters are tapping, it may be that you have good oil pressure, but collapsed lifters - so the best thing would be to replace the lifters.
WERE tapping (after the 30min highway run). Once I added the 2-1/2 of lube, the tapping went away and that's when I started getting oil pressure reading back on the gauge. Since the tapping went away immediately, I know it was due to low oil and only a temporary fault.
Quote:
I don't like the idea of heavier oil than 10W-30 for a Gen1 3.0L, but with sumnmer coming up, you could probably go a little heavier without causing trouble.
I didnt like the idea either - mainly because it's the cheapest and easiest fix - but not the proper one.
Quote:
Is the engine temperature ok?
Yes, so far so good - never went above 1/2.
Quote:
How many miles are on the engine?
Amazingly, only 130k
Jim
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MI_Mitsu
Rock Warrior
Reged: 03/24/06
Posts: 702
Loc: Romulus, Michigan (Detroit)
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Quote:
You and I have the same vehicle. We also had the same oil readings under the same driving conditions. When cold, the oil is thick and the pressure is high. When hot, the oil thins and the pressure drops. My pressure ranged in exactly the same ranges as yours.
Wanting the pressure to be a bit higher when cruising at highway speeds (20+ desired), I added Lucas Oil Stabilizer which has the effect of keeping the oil a bit thicker and keeping it up in the heads. It worked. I mix it at a ratio of 1 part Lucas to 4 parts regular oil.
The engine is much quieter now.
This is definitely good to know. I knew oil got thinner as it warmed like Frank said - but for the pressure to drop in half to nearly nothing after 10-15min I thought was drastic.
I often use the Lucas stabilizer myself, just never quite got around to changing this rigs oil when i bought it. The PO just had it done professionally at time of purchase and level was good and clear at the time. I only put 2500 miles on it in the past year.
Definitely time for a flush, change and stabilizer. Will report back after I accomplish all this later this weekend.
Jim
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Kevin C
Trail Leader
Reged: 05/20/00
Posts: 6033
Loc: No where in particular
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The question I would ask is there any damage to the bottom end? A oil change and filter inspection would show up any large bearing bits. Sending a sample to a lab like Blackstone would let you know for sure.
Kevin
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87 Dodge
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MI_Mitsu
Rock Warrior
Reged: 03/24/06
Posts: 702
Loc: Romulus, Michigan (Detroit)
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Quote:
The question I would ask is there any damage to the bottom end? A oil change and filter inspection would show up any large bearing bits. Sending a sample to a lab like Blackstone would let you know for sure.
Kevin
A good idea for sure - especially at this mileage and not knowing the FULL maintenance history. My worry is that sicne I added the 2-1/2 to 3 new quarts only 500 miles ago now, wouldnt I have diluted any major issue I had? Should I let the current oil just added circulate for another 500 miles or so?
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