4G63 OIL PRESSURE

Hello guys,

I just finished assembling my engine and I just wanted to know whether my oil pressure was okay, seemed a bit low to me.

Rod bearing clearances 2-2.2thou and main bearing clearances 2.3-2.5thou. The balance shafts are in place but i didn't replace the bearings because they looked perfectly fine. I am using 15w40 oil for the break in. So on cold start i'm getting 5.8-6 bar of oil pressure but once the car has warmed up i've seen as low as 0.6bar. At that point i decided to switch off the car. Is this normal or do i have a problem somewhere. I forgot to mention it has a new oil pump.

Should i run a thicker oil to increase oil pressure(Non MIVEC 4G63) or do i have an issue somewhere?

There definitely seems to be some sort of issue there. Have you tried checking it again when cold to see if it still has the ~6 Bar pressure?

If you're lucky the oil pressure regulating valve, the bypass, has stuck open and it just needs to be removed and cleaned carefully and checked for free movement.

This is normally a spring loaded piston where the oil pressure pushes it back to expose a return to the sump - this is used because otherwise the thick cold oil, especially when the engine is rev'd, can result in very high oil pressures that can cause some serious problems, like burst oil filters, or filters "jumping" a thread and loosening, to stripped/sheared oil pump drives (this was a BIG problem with the Ford Windsor and Essex engines that would strip their hexagon oil pump drives).

The problem is that if there's any debris in the engine, which isn't unusual even with very good cleanliness*, it can jam the piston in the open position and theis bleeds off the oil pressure.

It's a good practice to strip and check any oil pump, even new ones, and remove and casting flaws and relieve the sharp edges on the intake and outlet.

If you're moderately lucky, you forgot to plug something or tighten something, that you can simply remedy without any further issues.

If you're unlucky, you're going to have to pull the sump and a couple of big ends and mains to eyeball them for any damage.

An old machinist aquaintance had a sign with the three rules of engine building - 1/ Cleanliness 2/ Cleanliness 3/ Cleanliness.

Hmm okay. Before assembling the engine I stripped the oil pump and cleaned everything thoroughly. If the oil pressure regulating valve was stuck open wouldn't the cold oil pressure be extremely low as well? 6bar(87psi) on cold doesn't seem too low but correct me if i'm wrong.

I did check the oil pressure again on cold start after that, I got 6 bar

OK, hopefully some of the Mitsi' guru's will have a good idea what might be the problem, it's not something I've come across on other engines, IIRC.

What RPM you are idling at? What is the oil temp?

It's idling at 850-900rpm. It's got 272 cams in it, the idle is a bit rough if that makes any difference. Unfortunately I don't have an oil temp gauge for now

For that type of idle rpm 0.6 bar is a bit too low. It should be at least 0.8-0.9 Bar providing that the engine is not red hot with ambient temperature 30+ degrees C.

I would try to change oil for a thicker type,say 50 or even 60 just to see if that will help to increase the pressure.

Okay, this was helpful. I will definitely try a thicker oil and see if the pressure increases. Thank you guys for your input.

Something that might be part of the problem is if these engines use a restrictor or check valve to control the oil supplied to the head and it was left out - there could be an excessive internal leakage contributing to the pressure drop?

The only one such valve I know of that controls oil pressure in this engine and that's the relief valve in the oil filter housing. I have thoroughly cleaned it and made sure it's sitting right. According to the service manual the minimum oil pressure is 11psi. Currently I'm at about 9 psi but again I know the oil I'm running is a bit too thin for my clearances. Hoping to gain some pressure by switching to a 50wt oil. Do you think I'll gain enough pressure by switching from my current 40 to 50 viscosity oil?