1994 Mitsubishi - 4M40 Engine Breather Blows Oil

Did you do the re ring are did someone else do it. This is a symptom of blow by and these engines are very specific to assembly guidelines. Here is a link to a free service manual to the 4M40 engine.

http://www.onlinefreeebooks.net/automotive-machinery-power-equipment-ebooks/mitsubishi/mitsubishi-engine-4m40-workshop-manual-pdf.html

I would study the area dealing with the piston and rings and see if everything was assembled properly. and pay special attention to the letter identification of the piston to the cylinder as it is stamped on the block. A lot of people are not aware of this detail of the 4M40 Engine. Good Luck and hope it helps.

Yes went through the manual my self set the ring gap as specified sleeves are within tolorance no rig at all but still after running some 300kms oil is sucked via this breather pipe and ends up being burnt through the inlet strange you don't see any sign of oil or smoke at the tail of the exhaust pipe oil simply runs low

am thinking of using an external breather any idea ?

Have you checked the valve seals? That can cause blow-back

Valve seals and guides new! valve seats sealing well New turbo west gate open @ 1 bar

runs ok only this blow problem

I use Castrol Turbo Fleet SAE 15w-40 from South Africa. (vehicle operates in Uganda)

Note this Oil is commonly used in East Africa and never had any problems reported.

I have run in the engine now for 10000 kms But still this problem exists

I tried to contact other friends in Nairobi (Kenya) and they confirmed that they also faced the same problem and when they contacted Mitsubishi dealers they were replaced with New half engine Blocks complete with Pistons installed But No body tried to find out what the problem is.

may be Mitsubishi are hiding something?

Vercellese This appears to be the cause of your problem, this oil probly hasn't allowed the rings to seat, this is a critical step in breaking them in. I crew chief for two race teams and we had one engine this past season that the rings failed to seat. This was a brand new GM crate engine, we performed the recommended break in procedures and after four races we pulled the engine and found that on two cylinders the rings never seat. This required honing the cylinders and installing new rings. We use a straight 30 weight non-detergent for around 50 miles for our break in, then change to synthetic racing oil. J.Conway

On the ball!

You are right! I have been using synthetic for almost 20 years and the wear (and of course the "wear-in") is dramatically reduced.

With new VW TDI motors (I have had 5 over the last 12 years), the first 10,000 kms uses quite an lot of oil. Right up to 100,000 kms or so, the oil usage gradually tapers off.

I only consider a TDI engine to be fully "Run-in" when it has more than 80,000 kms on the clock......the oil usage is then usually down to a liter in 15,000 kms or less.....my present engine is running at 93,000 with about 0.5 liter per 15,000 kms....

Interestingly enough, on my earlier VW TDIs, the handbook required at least 5,000 kms to be driven before towing a heavy trailer, "OTHERWISE OIL USAGE MIGHT REMAIN HIGH FOR THE LIFE OF THE ENGINE"

Its not in any of the recent manuals, but I still follow this religiously and have had no problems........

Mate,

Worn valve stem seals will cause smoking at start-up but will have very litlle influance on oil usage..it will just do the exhaust system and rings some good!

You seem to have blow-by [Gas leakage past rings.... or rings skating on to much oil]

Vercellese. You stated the sleeves were within spec, was this after honing to true up and create a good lap pattern to help the rings to seat? J.Conway

Yes i used 2S Plateau honing just as per Technical highlights manual

Rings to groove clearance

1st = 0.03

2nd = 0.07

3rd Oil ring = 0.03 mm

Yes i used 2S Plateau honing just as per Technical highlights manual

Rings to groove clearance

1st = 0.03

2nd = 0.07

3rd Oil ring = 0.03 mm

If the above numbers are actually the end gap measurements then they are way to tight in the cylinders as the end gaps should be 1st and 2nd rings .3-.45 limit .8 mm and the oil ring should have.3-.5 limit .8 non turbo .25-.45 limit .8mm

2. Have you pulled the crankcase breather tube and seen how much blow by you are getting blowing out to atmosphere. If it has a large amount of blow by you have one of two problems.

A. Compression bypassing the piston.

B. Stopped up crankcase vent causing oil to be blown past the seals or gaskets which should be able to be seen by inspecting under the engine to see if there is any place that you can see an oil leak.

There is no sign of any leakage all engine is well dry.

The breather tube show a normal blow out

am suspecting either too much oil is going to the cylinder head or the top cover vent is a faulty design.

question is why would Mitsubishi send in New half engine blocks to replace the exiting ones? curiosity!!

am looking for an external breather vent to try out

SNATCH OFF THE VALVE COVER WHEN THE ENGINE IS SMOKING. USE PIG BLANKETS/SUCKUPS TO PREVENT A FIRE. TOP END OILING PROBLEMS ABOUND, EITHER ITS OVERPUMPING OR NOT DRAINING. SOUNDS LIKE YOU'VE GOT THE RING PROBLEM SOLVED, BUT I'VE PUT IN LOPSIDED RINGS WHICH NEVER SEALED. ONLY BY INSPECTING THE WEAR POINTS ON THE RING FACES DID I FIND MY FAVORITE BRAND OF RINGS (HASTINGS) HAD A BAD BATCH. MASS PRODUCTION HAPPENS. I STILL USE THEM IN THE RACE MOTOR.

Do the compression test on each cylinder again with throttle wide open, note each reading.

Pop a few spoonfuls of oil in a cylinder, make the test again. Then the next cylinder also with oil and pressure check....and so on for each cylinder.

If there is a 5% or more increase in pressure, then the pistons/rings are not sealing, if there is no difference, the valves are at fault!!

It may be only one cylinder at fault by the way.......

Sorry Andy,

Compression tests are of little use. Rather do a propper cylinder leakage test[Engine at working temp.; piston at tdc and compressed air through plug hole introduced throug tester.] This test can determine exactly if you have any one of the valves , or the rings and/ or gasket or cracks leaking. It is normal to have up to even 30% leakage past the rings and that would still not amount to eccessive blow by.

Valve leaking would not cause blow by.

I have seen Mercedes engines which had rings as good as baling wire having blow by from day one. I actualliy knotted these ring with my hands!!! [Mercedes are still......investigating....with NO re fund!]

....agreed if the person testing has the equipment. I understood that he did not have much, so I made the test as simple as possible......

He can make a choice of what he is able to do now.......

Your rings are not seating or the piston and sleeve are already oval. The other reason could be scratches on the piston or sleeve.

As your piston moves up and down in the sleeve, irregular oil changes, wrong oil, or the wrong grade of oil could accelerate the wear on your pistons.

When you replaced your rings, did you hone the sleeve?

Many backyard mechanics do not do that and then the new rings fail to "bed" in the honed cylinder.

Also check that you have the correct rings fitted as you get stailess steel or cast rings.

Thye gap in your ring ends are critical.

A broken ring could also cause the problem.

Please also check for a scraper ring,(The second one) which was fitted the wrong way around.

Ronny Moore

Hi , im no ace mechanic but i have been around engines for quite a while , my thoughts concerning your problem, are as follows.

I think your engine is probably fine as far as oil control rings and valves etc.

I suspect a simple design flaw in the breather pipe to air intake system .

That being said , im not sure why Mitsubishi would send out half engine blocks to correct this but " who knows " ?

Question ., is this problem with the P.C.V. system or a simple breather pipe ?

If the P.V.C. system is involved , make sure it is clear , make sure the P.V.C. valve is not installed backwards and generally check for proper operation.

If we are talking about a simple breather pipe from the valve cover to the intake then i would look for the absence of a deflector or baffle to prevent oil from simply being sucked into the air intake system , " the design flaw ".

Remove the valve cover , turn it over and look for a baffle at the breather pipe fitting, if there is none then there is nothing to stop the engine from simply sucking the oil that is flying off the valve train into the intake system .

Fix this by tacking a metal hood over the hole to prevent oil getting sucked in but leave an opening parallel to the valve cover to allow the engine to breath .

Hope this helps .

Gentleman i did change the Top cover on Saturday, replaced it with a new one and seems the problem is kind of solved i have run some 300 kms @ 140 kph and d`int notice any oil loss oh i did also change another type of air filter so it could have either been the Top cover vent problem or the previous type of air filter used.

Cross fingers!! still testing and will keep you all posted!

never the less i still wounder why did Mitsubishi replace for New Half blocks???

Mitsubishi replaced the "half engines" because they had to. Either Mitsubishi does not trust it's own trained mechanics to replace pistons and rings, OR, the factory knows that there is something wrong with their blocks.

It could be that the cylinder walls do not stay round after use. It could be a metal composition problem. But it seems that the engine block is the problem.

The wet to dry compression test will yield information. The cylinder leak down test will yield information. but the real answer is to use the time tested methods. dismantle the engine again and mike the bores all the way around, and all the way up and down.

If you want the answers, that is the way to find out. If your bores are out of round, you could re-sleeve it with replacement sleeves. The replacement sleeves are made of a better material than original blocks are usually.

Sounds like a lot of work now for just a little blow by.

I also had the same problem with a 4m40 engine, thus i took off the rocker cover and flushed the breather with caustic soda and hot water, a lot of messy sludge came out of there . problem fixed no more oil loss.

If the engine cylinders were within spec's when you had new rings fitted and the pistonring clearence in their grooves where ok then ......the oil pressure might be to high causing the ring to plane on the excess oil beiing squirted on the cylinder walls!!!

Check oil pressure and bring down oil pressure to the lowests specs of manufacturer at the pressure relief valve by the oil pump or on the main oil gallery.[Lowering the relief valve sping tension]

Before the above: Make sure the glaze on the cylinder walls were propperly removed by honing the cylinders and that top-class rings were fitted!!!

Jurie za

Hate to say this, but that is a wonderful Fairy Tale, I laughed my socks off.LOL

Andy,

I love German cars,got a Mercedes myself. On the 230/4 they did not dril oil holes in the oil rail to lub the exhaust lobes of the camshaft and many had to have camshafts replaced! Any manufacturer sometimes slip up!

You can keep your socks on, I have proof about the dud rings that was fitted to a batch of Merc 200's. No reason to talk nonsens.

Mercedes are far From being my favorite car, I see from relatively close up how they bodge fixes and overcharge customers for spares......as do BMW.

Some of their mistakes are passed onto the customer to pay for.....about 10 years ago, you had to buy a complete rear axle if the sensor broke for the ABS!!! Instead of like $10, they charged $6000......now that is bad planning........don't buy any T models of the late 80's and 90's with ABS by the way.....the problem has not been fixed, at least not here in Germany.....

Both Mercs and BMW have somehow conned the world into believing that they are good. Bu to my mind neither are cars for people (retired) with limited means at their disposal....like myself.

My favorite German make is Audi, we have one as a second car and our main transport is a Diesel Mitsubishi Grandis, my favorite Marque of Japanese cars for many years now......my presnt Mitsubishi has a VW 2.0 TDI Diesel engine as the Mitsubishi Diesels, although reliable are not good enough with consumption for the Euro market.

Clean the aircleaner vent valve in the tappet cover will cure it.

Or replace the tappet cover.

finaly i managed to hve a chance to see the new type of the 4M40 engine and guess what!

the Piston and Rings were modified,it was enough for Mitsubishi to release a TSB concerning this problem, but for some reason they decided to hide this problem

and just supplied new half blocks with pistons ready inserted, to their dealers and keep muum. same thing regarding

Toyota Rav4 A/T problems that are caused by a faulty ECU, but never mentioned, Shame!!!!

Wrong blog, comment erased.

My 96 challenger had this problem, about 1 litre every 100ks was disapearing fast, no oil leaks and no blue smoke turbo and intercooler were full of oil. I developed a fix for this and now my one is perfectly dry and uses no oil.

So, how'd you fix it?

Yeah, what Hush said.

What was the problem (how did the oil get in the turbo) and how did you fix it?

Thank for jumping in with that. Creative solution!