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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
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Experience:  23 Years Caterpillar Engine experience.
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I have a 3306 Cat Engine. It had an in-frame major done a year

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I have a 3306 Cat Engine. It had an in-frame major done a year and a half ago by my Cat dealer. Everythings been working good until 3 weeks ago. While on a job in AZ, it started blowing oil out the exhaust. ( It doesn't have a turbo. ) I had a Cat dealer put an exchange head on in the field - nothing. Still blew oil. ( They test the first head - it was all good.) I brought it back to my shop & had the same Cat mechanic come over. He took off the head & pull the pistons - all looked good. We put a new set of rings on - just because. Nothing - still blew oil. Tested oil pressure & was getting 120 PSI - cold. I had him put a exchange oil pump on and pulled the by-pass valve out at the filter housing. Still 120 PSI. - Still blowing oil out the exhaust! Please help!

Hi. Thanks for using JA! I will try and help you out.


When you say it is blowing oil out of the exhaust, how bad is it? Is there a lot of smoke? It the oil literally coming out of the exhaust and getting all over everything?


Also, how is the power of the engine? Good? Weak?



Customer: replied 4 years ago.

The power is excellent. No bad smoke, but oil coming out the muffler & getting on everything. ( Too much slobber for any job site EPA type person. ) When we ran it with the exhaust manifold off, oil coming out all ports? Help!

Thanks for the information.


If you have changed the head and the piston rings, the cylinder liners are the only thing left. There must be oil getting past the rings due to a loss of crosshatch or wear. I will say this is very odd. The only time I have seen this type of oil coming out of the exhaust is when the engine has bee run hot, or the engine has ingested dirt in the intake and cause wear on the cylinders.


Have you inspected the intake for dirt entry?

Customer: replied 4 years ago.

The cross hatch on the liners was still good, except for some slight scoring from carbon build up on the top of pistons on liners #'s 2, 3 & 4. We ran a hone & they came out relatively quickly. The most amazing thing about about this engine is the oil. It is absolutely perfect. I mean so clean - if you take some out & put it in a glass jar, it would look identical to new oil. This engine is 25 years old! We thought that something happened on the job site & they just changed the oil. But even if they did that ( which they say they didn't ) it still had on the oil filter I put on with my handwriting the date! In five seconds of running through & mixing - it would be blackened! We've run it around for 1/2 hour here & the oil still looks perfect! Nobody's ever seen engine oil this perfect! Is that oil pressure just too much, and if so, what else can I try?

Thanks for the information.


The oil pressure is high. Everytime I have seen oil pressure this high, it was a bad oil pump (which you have already replaced) or a restriction in the block after where the oil pressure is being measured.


I must assume there is something wrong with the liners. Even though they looked good. Since your engine does not have a turbo, and the head and rings have been replaced. The liners are the only thing that is left.



Where are you measuring the oil pressure at?

Customer: replied 4 years ago.

We are taking the pressure at the port that is used for the guage in the dash - left side of block. Would you change the liner's & pistons & another set of rings - or just the liner's? Or, try to continue to chase the oil pressure being so high?

Thanks for the information.


I always like changing the liners and rings at the same time. Many times when only one is changed, the engine will consume engine oil.


I would also recommend removing and inspect the oil cooler and oil filter assembly. If there is some sort of restriction or problem there, it could cause your high oil pressure problem.

Customer: replied 4 years ago.

It doesn't have a fuctioning oil cooler - it is blocked off by factory. ( We took it off before the in-frame major & saw the ports are simply blocked - we guessed for some cold weather application ) But I've had this machine for 20 years and it's never been an issue. But I'm in California & this last job was in AZ....It's never been there! Maybe because of the high heat there - the fact it doesn't run an oil cooler DID have an effect on the rings & liners???

I see. Thanks for the information.


I was not aware it did not have an oil cooler. There is a good bit of difference in California and Arizona. The heat in Arizona may very well be the factor that is causing your problem. With the heat being much higher, the engine may have needed an oil cooler. If the engine did need an oil cooler, it would directly affect the rings and liners. It would cause them to wear more than they should with the oil getting too hot. When it gets too hot, it gets thin and can not do its job like it should.

Customer: replied 4 years ago.

If we mic the liners & they are to spec's, would you still change them? Could they expand, now, when hot & back to with-in spec's when cold or is that not possible? They look very good to the eye - still having the original cross-hatch scratches - except for now we honed them.

If they are in specs, you should be able to just hone them again. Then check and make they are still in specs.


With the engine not having an oil cooler in the hot temperature, the oil is most likely getting so thin, it is passing by the rings. At the same time, the rings and liners are getting some wear due to the fact that the oil is a little to thin to lubricate and protect.

Customer: replied 4 years ago.

But we did hone them & put a new set of rings in. And, it's back here in CA - still blowing oil. We should have mic'd the liner's, but now if we do pull it back apart & mic them and they are with-in spec's, would you change them out? Getting so hot over in AZ and it not having the oil cooler - could the liner's have weakened so when it run's here - the liner's expand each time? Or is that not possible?

Then I would replace them for sure. I would think they are not within specs if you have honed them and it still passes oil. Not possible for them to weaken. The liners are a very tuff hardened part. They can only wear on the inside.
Customer: replied 4 years ago.

Ok, lastly for now - ( Obviously if they are not to spec's - we found our problem and will replace them ) however, if they are to spec's, any last direction to go?

If the liners are within specs, the next thing I would look at is the piston ring lands. It is also possible for the rings lands to have wear and cause oil to pass by.

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Customer: replied 4 years ago.

Ok, we took the head off & mic'd the liners. The first thing we saw was scoring in most of the liners - more than BEFORE we rolled in a new set of rings! The liners mic'd anywhere from .002 wear to only .0005 in a couple. Well within spec's, but I thought .002 was a little much for only being 1 1/2 year old rebuild? The scoring is leading us to believe the lands on the piston's are bad, and when we put in the new rings, it made the problem worse? ( We ran it about two hours - total - since putting the new rings in. ) We are pulling the piston's out now, but they didn't look bad before - to the naked eye. Any suggestions now? And would you replace the liners?

Thanks for the update.


I would replace the liners. If they have scoring, by the time you hone them, you will have removed more metal from the liner. If you replace them, it will be like new and last for a long time. To be honest, I would also replace the pistons and rings. I think it would just be a better repair by dong so.


Let me know if you need more help or have more questions.

Customer: replied 4 years ago.

Ok, I ordered the cylinder packs - then everythings new & correct. This is the forth time opening up this engine by a Cat dealer mechanic. So, labor cost alone is gonna be brutal - not to mention probably $10K in parts! We put an exchange engine oil pump on because of the high oil pressure - but it didn't change anything. The mechanic still has my pump on his truck. He can put mine back on & at least save me $500.00 - there. Would you do that? And what about the high oil pressure? Just live with it or what? I can't find any written documents that tell us - maximum oil pressure - for a 3306 engine? Only minimum...

The maximum oil pressure when hot is 90 psi. If the engine is cold, it will be a little higher.

Yeah, you could put it back on. I would if the pressure is the same.

I hate the pressure is that high. I would remove and inspect the oil cooler spray jets. Maybe they are.restricted. That would explain the high pressure and liner damage.
Customer: replied 4 years ago.

There are two ports on the top of the filter housing for the relief valves, but since the oil cooler is factory blocked off, there is nothing in the left or front port hole - it's empty. Then we removed the right valve, for the filter, inspected it - looked fine and put it back in & ran the engine. Same high pressure. Then we took the valve back out - left it out - ran the machine. Still the same high pressure? Anything left to try?

I see. Thanks for the information.

That is odd. I would have thought by leaving it out, the pressure would have went down. Not sure what else to try. Sorry. From my experience, oil pumps normally cause this, but since you have changed the oil pump, and removed the valve in the filter, not sure what else would do it.
Customer: replied 4 years ago.

Ok, thanks. I hope that it's not going to cause a problem. We'll put back together and run it. Lastly, a better question might be - what problems would running extremely high engine oil pressure cause?

The only problem that can come from high oil pressure is it could cause an oil leak at a gasket or seal. It will not hurt any parts in the engine. As long as the engine does not develop a big oil leak. The engine should be fine.