Cold start oil pressure slow to rise: check my thinking

[Disco95]

Hi all,

95 3.9 V8 (so the weirdo new-style oil pump w/ distributor setup) is slow to build pressure when cold (like 10-20 seconds for the light to go out). The colder the day and the longer it's been sitting the longer it takes. Warm starts are quicker but can still take 1-5 seconds. Here are the clues so far...

• swapped pressure switch, and confirmed with separate oil pressure gauge -- no change
• oil pressure seems fine once it's up (38psi cold or hot at 2500 on a mechanical gauge at oil filter housing)
• last oil change went from 20w50 to 15w40 (Rotella) with Mahle Black OEM filter -- seems to be slightly improved but maybe placebo, still too long
• engine makes no nasty noises while light on, but there is some tappet noise after ~30s. This noise comes and goes at idle but honestly is no worse than our old EJ22 subaru with hydraulic lifters -- concerning?
• engine runs smooth and strong in all conditions

My understanding: 1) oil is picked up from the sump, 2) passes through the oil cooler (even when cold?), 3) through the filter/bypass, 4) on up the engine. From the behavior, it seems like oil is either having a hard time being picked up (1), getting through the cooler (2), or is just draining back to the pan more than designed(?). There are a few similar accounts of this phenomenon on the net, but there doesn't seem to be a common solution. That said, I didn't see anyone who really went step by step through the process--most started throwing pumps and bearings and engines at the problem to solve it!

The truck isn't a daily driver so I can afford to take my time. I'm looking for "pragmatic" more than perfect with this engine. It has 200k miles and 50k on a "rebuild" of unknown extent and quality. I imagine a proper rebuild is on the horizon. I'd like to at least take all the simple steps to identify this issue but without sinking more time and money than makes sense. Wrenching time is limited, so I'd also like to avoid doing things twice!

Thanks for your help!
joe in pdx

(startup video, ~68 deg day, first start)

 

[Jimmy]

Motor Oil 101 - Chapter One - Operating Temperatures and Viscosity - Bob is the Oil Guy

Chapter One Understanding what viscosity grades mean can be confusing. The average driver just tries to follow what is in the owner’s manual – this is a good practice. Some owner’s manuals allow for different grades based on the predicted operating temperature. For example, they may specify a...

bobistheoilguy.com

Try a 5W-40. Despite all the noise that's going to appear in this thread it's ok to run a 5W in these engines when needed.

 

[Gordo]

I’d change the gears in the pump if it was mine. I had a set grenade on a D1 gems at 151k. I’d drop the pan and put a new gasket under the pick up too and make sure everything is happy. May wanna drop a rod cap to check the bearings while you are right there. U can swap all the crank/rod bearings underneath with the pan off. It’s not too hard. I did it while I was at it since I bought the truck with the bad oil pump and they were well worn. You probably won’t see too much wear at 50k.
another option is a pre Oiler. I have one from an old diesel build. Turn the key wait 3-5 seconds and the pressure is there before you start. Real nice to have

 

[Disco95]

I’d change the gears in the pump if it was mine. I had a set grenade on a D1 gems at 151k. I’d drop the pan and put a new gasket under the pick up too and make sure everything is happy. May wanna drop a rod cap to check the bearings while you are right there. U can swap all the crank/rod bearings underneath with the pan off. It’s not too hard. I did it while I was at it since I bought the truck with the bad oil pump and they were well worn. You probably won’t see too much wear at 50k.
another option is a pre Oiler. I have one from an old diesel build. Turn the key wait 3-5 seconds and the pressure is there before you start. Real nice to have

Thanks, Gordo! I've got the pickup gasket and oil pan gasket on hand. Wanted to wait and decide whether I wanted to pull the front cover or not so I don't have to do the pan twice. Sounds like maybe I should? A catch is I've had trouble locating a timing cover since I think this was only a couple year run for the crank-driven oil pump plus dizzy setup. Do I understand right that the cover and gears need to be a matched set? Or is it ok to just swap gears if the cover checks out? If I get in there I'll probably want a chain on hand, too...pretty soon I'll have it down to the chassis like my IIa.

The pre oiler could be interesting as a stop gap. How invasive is it? Electric, I take it?

Cheers,
joe in pdx

 

[Disco95]

Motor Oil 101 - Chapter One - Operating Temperatures and Viscosity - Bob is the Oil Guy

Chapter One Understanding what viscosity grades mean can be confusing. The average driver just tries to follow what is in the owner’s manual – this is a good practice. Some owner’s manuals allow for different grades based on the predicted operating temperature. For example, they may specify a...

bobistheoilguy.com

Try a 5W-40. Despite all the noise that's going to appear in this thread it's ok to run a 5W in these engines when needed.

Thanks, Jimmy! Seems worth a shot! I'll learn something anyways. I put 0w30 in a 300k mile Volvo 240, and it didn't mind at all despite all the warnings against it. Any recs? 5w40 seems like a big range for a conventional oil, or maybe that's outdated, too?

Cheers,
joe in pdx

 

[Jimmy]

Thanks, Jimmy! Seems worth a shot! I'll learn something anyways. I put 0w30 in a 300k mile Volvo 240, and it didn't mind at all despite all the warnings against it. Any recs? 5w40 seems like a big range for a conventional oil, or maybe that's outdated, too?

Cheers,
joe in pdx

5w-40 will be synthetic. I run Rotella T6. The ton of detergents in it will help gently clean the inside of the engine over time.

I totally missed the "~68 deg" right below the video the first time. Certainly does not qualify as a "cold" day. No 5W needed for that. Living in Colorado, single digit temps drove me to a synthetic 5W to keep the oil pressure light away.

 

[4Runner]

When I cleaned the screen on my oil pick up, it made a big difference in the time it took to build oil pressure on my 96. Haven’t had to touch my 94 yet.

 

[Gordo]

Yes a dirty screen could easily do it. Your existing Timing cover should be fine. You can just replace the pump gears if need be. They sell them fairly cheap. There are several Phillips bolts holding the pump plate on the backside of the cover. Remove that for access to the gears. A quick leveling of that plate of any groves helps too. I wet sanded mine on a piece of flat glass. May wanna just try the oil screen, pick up and sump first. Good luck

 

[Disco95]

Updating this thread. I kept putting off this messy job but finally had the timing cover spring a coolant leak and force my hand. I'll write that process up in another thread, but suffice to say, whatever shops charge for that job isn't enough!

I can now add a few things to the list of stuff NOT responsible for the oil pressure issue (slow to rise on cold start):

• was really hoping for pickup screen, but it was clean as a whistle; think someone had been into the oil pan recently; replaced gasket (no or-ring on my 1995; pickup tube routes through the block directly to oil pump)
• next best hope was bypass/relief spring (only one on my 1995, above the oil filter); nope, free, clear, and length in spec; replaced o-ring seal
• next up oil pump gears; nope, looked great; some minor scoring on cover surface, but wouldn't that affect warm OP more than cold?

I'm at a loss and probably will just run it at this point. I'll report back if it blows up or I have some inspiration!


gears looked ok, decided to roll with them instead of playing BritPart roulette. The pics make the very light scoring look a lot worse.


case looked decent too; again scoring much less apparent in person, can just feel it with a fingernail


Cheers,
joe in pdx

 

[discostew]

Motor Oil 101 - Chapter One - Operating Temperatures and Viscosity - Bob is the Oil Guy

Chapter One Understanding what viscosity grades mean can be confusing. The average driver just tries to follow what is in the owner’s manual – this is a good practice. Some owner’s manuals allow for different grades based on the predicted operating temperature. For example, they may specify a...

bobistheoilguy.com

Try a 5W-40. Despite all the noise that's going to appear in this thread it's ok to run a 5W in these engines when needed.

But what about 40 wt. Cause to me thats the number that means the most.

 

[p m]

Going back to the beginning - what is the oil pressure at the start-up at idle?

 

[Disco95]

p m: I confirmed with a mechanical gauge that it’s near 0 while the oil light stays on for 5-30 secs (longer the colder it is outside, but it’s never much below freezing here). Pretty confident I’m getting flow though—engine sounds good. It then immediately rises to ~40psi and stays there. No issues after that.

Decided to stick with 15w40 for now to see what the clean up might do. Might try 5w40 or 10w40 next change for kicks.

thanks,
joe in pdx

 

[p m]

Oh wow.
My 95 Classic's oil pressure light stays on longer than 96 Disco's, with the same idle speed and oil pump.
I guess I need to check the pressure with a real gauge.

I was always drawn to things like this, but in reality... the D1's cylinders still had factory cross-hatch marks, and crankshaft rod journals were maybe 3 thou under, at 250 kmi.

P.S. I don't know what oil filter you are using - the anti-drain-back valve in it may be hosed.

 

[discostew]

Did you look at the pressure control valve? Like p m said it seems like it’s leaking down and having to prime itself on startup Then once that all happens you say you have 40 psi which kind of seems like too much.

 

[Disco95]

Oh wow.
My 95 Classic's oil pressure light stays on longer than 96 Disco's, with the same idle speed and oil pump.
I guess I need to check the pressure with a real gauge.

I was always drawn to things like this, but in reality... the D1's cylinders still had factory cross-hatch marks, and crankshaft rod journals were maybe 3 thou under, at 250 kmi.

P.S. I don't know what oil filter you are using - the anti-drain-back valve in it may be hosed.

The truck had a no name white filter on when I bought it. Replaced with the black Mahles so should be good there. It's definitely weird, but I bet it's been doing it for a lot of the 200k miles, so I think at this point I'll leave well enough alone. Thanks for the notes!

-joe

 

[Disco95]

Did you look at the pressure control valve? Like p m said it seems like it’s leaking down and having to prime itself on startup Then once that all happens you say you have 40 psi which kind of seems like too much.

The valve was sliding smoothly. The spring was a little long for spec (~64mm instead of the 60mm by the book), but like you say that would only explain high pressure. The pressure's in spec at 2k RPM (~40 psi). I can't find my notes on warm idle pressure but wanna say it was around 25-30. I'd like to cut the oil cooler out of the equation and test at some point. It seems like a restriction there could maybe cause something like I'm seeing (I think, the flow path to the sensor is hard for me to pin down), but I've never heard anyone mention a plugged cooler.

Cheers,
joe in pdx

 

[discostew]

To have that much oil pressure hot is great. Did you look at the sump yet? What if it’s restricted? Once the pump makes the pressure it should just be able to maintain that pressure pretty easily.
Unlike a fuel pump pushing thru a restricted filter. The needed volume of fuel will go way up under load and the pump won’t be able to maintain the pressure. The needed volume of oil won’t go up at all. So the pump can maintain the pressure even thru a restriction. Once it’s made pressure.

 

[geoff]

If you have good hot oil pressure, checked the oil pressure relief spring, then I would suspect the oil filter. Are you using one with an anti-drainback valve? The WIX 51068 works great for me. 5w-40 is definitely the grade for this engine. 20 years ago 20w-50 yes. Mobil 1 Turbo Diesel truck works best in my experience. I would use Rotella T6 5w-40 if you can't find Mobil TDT. Rotella is a good option but I have less lifter noise at start up with the Mobil 1 TDT. The Mobil 1 Euro 5w-40 FS spec works well too.

Diesel oils have more zinc which helps with the flat tappet cam.

 

[Greg_M]

I was always drawn to things like this, but in reality.

I still have one of those! On the shelf until I decide which engine is deserving. I used it every start/stop for years on my Chev swapped IIA. Loved it!

 

[Disco95]

If you have good hot oil pressure, checked the oil pressure relief spring, then I would suspect the oil filter. Are you using one with an anti-drainback valve? The WIX 51068 works great for me. 5w-40 is definitely the grade for this engine. 20 years ago 20w-50 yes. Mobil 1 Turbo Diesel truck works best in my experience. I would use Rotella T6 5w-40 if you can't find Mobil TDT. Rotella is a good option but I have less lifter noise at start up with the Mobil 1 TDT. The Mobil 1 Euro 5w-40 FS spec works well too.

Diesel oils have more zinc which helps with the flat tappet cam.

Running 15w40 Rotella and Mahle (black, short) filter. So think I’m good there but plan to try 5w40 next change as an experiment.

One thing that has me wondering about these "intermediate cover" trucks is the different pickup system. The GEMS 4.0 trucks and later re-routed the pickup tube to go all the way to the front cover, popping out under the oil pump cover at an o-ring sealed junction. On older ones like mine, the pan pickup routes through the side of the block, through a hole in the the front cover gasket, then dumps into the oil pump. Maybe they had a good reason for re-routing, but it sure makes me wonder if somehow the old system didn't play as well with the new pump. Searching around it seems most common in Rangies and Disco's with the 3.9 or 4.2, which supports the idea. Probably I'm chasing wild hares at this point, though!

Cheers,
joe in pdx