CAT 226B oil pressure weirdness

I have been helping my neighbour with his CAT 226B. It has the infamous CAT/ Perkins/Shibaura 2.2 turbo in it (404C-22T). With only 1600 hours on it, the oil light started to come on.

I fitted a capillary pressure gauge in the cab to see what was going on. The oil pressure started out cold within range, but after the engine wamed up, the pressure dropped to near zero. The weird bit is that after shutting down for a few seconds, on restarting, the oil pressure improved by 10-15 psi.

Interestingly, the previous owner noted a warranty repair to the oil pump pickup at 500 hours. The local dealer denied that any such work had been done, but although I did not believe him, I could not see what motivation he had for not telling the truth. Needless to say no further warranty repair was forthcoming. So it was up to me to investigate.

I cleaned out the sump (as best I could without dropping the pan, as you have to lift the motor to do that) and changed the oil - no difference.

I pulled out the oil pump and replaced it. A bu&&er of a job without taking the engine out! The oil pump had been incorrectly installed from new. The idler gearwheel lubricating hole that should have been at 9pm was instead at 11pm, thus obscuring 3 of the 5 oilways. The pump rotor was moderately worn, with a couple of minor scores on the rotor.

OK, better oil pressure all round, but still eventually doing the slow drop in pressure and quick recovery after stopping for a few seconds.

As the cold oil pressure was starting out a little on the low side (around 40 psi) I also replaced the oil pressure relief valve. Now I have 58 psi cold, and still doing the slow drop and quick recovery after stopping.

I have even dismantled the old relief valve, polished the piston and bore to ensure it could not stick open, and reassembled with some packing to up the spring tension a bit. I now have fantastic oil pressure cold, but still doing the same thing on warm up.

Incidentally, this machine has been well looked after, with appropriate oil changes, using CAT brand oil and filters. The engine never gets above 80 degrees, and the sump never above 100 degrees even after working hard.

I am puzzled.

Did you pull any main bearing to see if the initial low oil pressure caused any damage there?

Thanks for the reply, but no, I did not check the main bearings. To do so requires dropping the sump, and that requires lifting up the engine. I am not really a mechanic, so that seemed a bit daunting. I am assuming that the lower oil pressure when hot is due to worn mains, although there were no metal flakes in the oil (or in the filter according to the local CAT distributor, who claimed there was nothing wrong with the engine). But I do not see how worn mains explains the recovery after standing a few seconds.

Sounds to me like something is slowly getting sucked up blocking flow dropping pressure. When turned off
Pressure relieved, obstruction dissipates . What could cause this ,I don’t .

I know nothing about the particular engine you're working on, but could the cause be a "drain back" issue? I have seen instances of engines nearly pumping themselves "dry" because oil was not draining back to the sump/pan quickly enough. The oil was getting restricted by partially clogged return passages. Maybe pull the valve cover and check out the oil flow? Just a shot in the dark.

SimS

The oring on the sump pickup could be bad or the screen clogged up. I rebuilt 5 or so of these engines most have rods out the side when I started.

is the engine building crankcase pressure

Sorry about the long delay, I have been pre-occupied with other stuff.

First, further investigation reveals that the oil is full of bubbles after a few minutes running. That would explain the rapid recovery in a matter of seconds. I have heard that these can suck air through a cracked pickup tube. So i looks like I will need to drop the oil pan after all.

SO!
Can I lift the engine enough just by disconnecting the rear engine mount plus the R side engine mount (that is all that is visible in the engine bay)? Or is do I need to remove a further mount on the hydraulic pump?

As I recall you will need to remove the engine from the machine to be able to remove the oil pan.

djm16 said:

Sorry about the long delay, I have been pre-occupied with other stuff.

First, further investigation reveals that the oil is full of bubbles after a few minutes running. That would explain the rapid recovery in a matter of seconds. I have heard that these can suck air through a cracked pickup tube. So i looks like I will need to drop the oil pan after all.

SO!
Can I lift the engine enough just by disconnecting the rear engine mount plus the R side engine mount (that is all that is visible in the engine bay)? Or is do I need to remove a further mount on the hydraulic pump?

Click to expand...

The pump hangs off the engine it would be much easier to pull the engine out.

Have you been able to locate the problem I have one I just rebuilt and it's having the same problem

I have still not got around to looking at this again. The engine has to come out, and I only have the one workshop repair area, and my '63 Rover is in it for an engine rebuild likely to take months. However, I am getting more convinced that the problem is the O-ring in the oil pickup tube.

While waiting for shed space, the machine is still useable but with heavier oil (20W-50) plus over-filling the sump! With the oil at the usual level and after standing a few weeks, the oil pressure would not pick up at all. I am embarrassed at how long I tried before trying something else. In the end, adding an extra couple of litres of oil led to almost instant oil-pressure.

The fundamental problem is that unlike most cars I know, the oil pump sits above the level of oil in the sump and is reliant on there being no air leak between it and the oil.

Rlh59 - Did you replace the oil pump? and are you sure you fitted it in the correct orientation, as there is no locating dowel or similar to make it fool-proof. If over-filling the sump fixes your problem then chance are that it is the O-ring. If over-filling does not fix it, I would look at the oil pump again.

Yes I put a new oil pump in it and used a alignment tool to install it
I did a complete rebuild and was able to test it on a engine stand .
It had about 50 lbs oil pressure I only ran it for a few minutes thinking 50 lbs was good idling
I installed a week later and started it and 0lbs oil pressure . I filled the sump full of oil still no oil pressure so I removed the motor to check the pickup, tube it was loose. I ordered a o ring from Cat and installed the new o ring
now I have 55lbs oil pressure for about 5 minutes then it drops to about 10 lbs at idle and about 30 at high idle . Maybe I will try (20W-50) to see what happens
Thanks for the information

After the engine has been stopped a day or two, how long does it take from startup to develop any oil pressure at all?

About 5 to 10 seconds it develops oil pressure
I ran it today at idle for 10 minutes started at 55 lbs when I shut it down it was at 20 lbs

5 to 10 seconds is too long! There has to be air below the pump. So only two possibilities there, 1) all the oil draining back through the oil filter and emptying all of the oilways - somehow I don't believe that OR 2) the O ring is not sealing, and the pickup tube is emptying.

the hot idle pressure is not too different to mine (with new pump and thicker oil), but I would be more interested to know what the oil looks like immediately after moderately prolonged working. So if you suck off a syringe full via the sump drain tap, is it full of bubbles?

I would be interested to know if you get yours fixed satisfactorily, as eventually I will have to fix mine too.

Hey, what did you find out with your liking issue? My 226b2 oil light starts to flicker when the engine is hot, raiding RPM about 100 makes it go off again.