4M40 Cylinder head gasket problem

[chaddy]

Good day fellas,
I know this is a very common topic but since happened to me 3 times within 2 years, I thought of opening my own thread.

I've got a 1994 Intercooler Turbo Pajero with a 4M40 imported engine. When I bought it from the previous owner he changed a brand new turbo for me (TD04 with water cooled).

On my way home the head gasket gave up, so I installed a new cylinder head, gaskets, and head bolts.

After 1 year & 9000km's later the head gasket gave up again. So I machined the head and installed another head gasket with new head bolts.

Recently I installed a SAAS Boost gauge and found out I'm boosting up to 15psi when my mates' pajeros goes only up to 8~9psi. I didn't take that so seriously.

But last week (1 year after installing the head gasket) I found out that it is losing water and there were some powder material in the radiator cap. So I'm thinking I've done a head gasket again.


This time I need to sort this out once in for all so I'm looking for other group members' opinion on this. If there is a 4M40 GURU in Victoria, I'm happy to take my car to him.

Thanks for reading my long question and feel free to comment your thoughts on my matter.

[Mcreight911]

When were the injectors last checked . Normally the problem is caused by heat . An injector that has poor spray pattern, dribbles or has extremely low crack pressure would be what I’d look for.
15psi boost will not cause enough combustion pressure to to it . I’ve run 35psi testing and 26psi+ for over 150000km with no head gasket issues.

[erad]

Somewhere in the fast fading memory of mine, I recall that there were problems with the 4M40 heads cracking. Maybe your head has a fine crack somewhere? I know it was a new head, but not everything is perfect. Possibly you could get a gas analysis done of the coolant to check for presence of combustion gases.

Another cause could be the block. Is the surface dead flat, or is it totally cleaned before installation of the new/refaced head?

There is a place in Nunawading where years ago I took the cylinder head from my wife's Magna. They did an excellent job, including repairing cracks, line boring the camshaft, pressure testing and lapping the valves, at a very moderate price. It is
Nunawading Engine Clinic, 6A Beech St Nunawading 3131, tel 03 9873 3462

https://www.nunawadingengineclinic.com.au

No commercial connections with them for years now, and hopefully it will stay that way.

[chaddy]

When were the injectors last checked . Normally the problem is caused by heat . An injector that has poor spray pattern, dribbles or has extremely low crack pressure would be what I’d look for.
15psi boost will not cause enough combustion pressure to to it . I’ve run 35psi testing and 26psi+ for over 150000km with no head gasket issues.

I haven't checked the injectors at all from the beginning. But visually they were clean every time I replaced the head gasket and I used injector cleaner a few times.

So this time, before replacing the head gasket, I'm hoping to take it to a good diesel tuning place so hopefully, they will have some answers for me.

[chaddy]

Somewhere in the fast fading memory of mine, I recall that there were problems with the 4M40 heads cracking. Maybe your head has a fine crack somewhere? I know it was a new head, but not everything is perfect. Possibly you could get a gas analysis done of the coolant to check for presence of combustion gases.

Another cause could be the block. Is the surface dead flat, or is it totally cleaned before installation of the new/refaced head?

There is a place in Nunawading where years ago I took the cylinder head from my wife's Magna. They did an excellent job, including repairing cracks, line boring the camshaft, pressure testing and lapping the valves, at a very moderate price. It is
Nunawading Engine Clinic, 6A Beech St Nunawading 3131, tel 03 9873 3462

https://www.nunawadingengineclinic.com.au

No commercial connections with them for years now, and hopefully it will stay that way.

The first time when the head was brand new, I didn't check it at all. But the second time I sent it to a machining place and the tested it for cracks, did boring the camshaft and grinded the valves. They said the head was fine.

I didn't check the flatness of the block but it was well cleaned and I used the special spray on the gasket as well.

[Kingmarz]

15psi is fine for this engine I was running 23psi on mine for 45,000 kms. I would say it’s more likely the install procedure or head and deck surface not being perfectly flat or clean and also make sure your hands are clean snd try not touching the surface of the new gasket also are the head bolts the stretch type and if so were the stretched before final torque up? Might be better using old head bolts as they’re pre stretched. Did you use lube on head bolts threads and both sides of washers cos if not it will give incorrect torque readings and also are you using antifreeze in the coolant system to prevent corrosion. The 4m40 can be a little unforgiving with the head gasket because of very high compression ratio of 21-1. I would consider installing an after market temp gauge to make sure your injection system is working properly and not causing excessive heat ss the factory temp gauge is rubbish and won’t move from half unless there’s a 33% change in temperature which in some cases with the 4m40 it’s too late.
Best of luck with it.

[Dongskie2]

Your coolant temp sensor could be faulty and may be sending a false reading.

If it isn't too late, I'd like to suggest that you also replace the coolant temperature sensor with a new one.

I have the same 4M40 and when I got it the coolant temp would always go up 1/3 of the gauge which I believe was wrong.

I replaced it right away and it now shows the correct coolant temperature on the gauge which is just below the half range.

When coolant temp sensor is faulty it will send false reading, like mine it was only sending 1/3 temp on the gauge when its actually already 1/2 temp. Or excessively hot when its actually not.

Chances are the engine could already be running hot at 2/3 of the gauge when its only showing 1/3 and mine as the sample.

Just a share from experience.


I agree with Kingmarz on an aftermarket temp gauge, i got one of those digital ones online. Works well!

[chaddy]

15psi is fine for this engine I was running 23psi on mine for 45,000 kms. I would say it’s more likely the install procedure or head and deck surface not being perfectly flat or clean and also make sure your hands are clean snd try not touching the surface of the new gasket also are the head bolts the stretch type and if so were the stretched before final torque up? Might be better using old head bolts as they’re pre stretched. Did you use lube on head bolts threads and both sides of washers cos if not it will give incorrect torque readings and also are you using antifreeze in the coolant system to prevent corrosion. The 4m40 can be a little unforgiving with the head gasket because of very high compression ratio of 21-1. I would consider installing an after market temp gauge to make sure your injection system is working properly and not causing excessive heat ss the factory temp gauge is rubbish and won’t move from half unless there’s a 33% change in temperature which in some cases with the 4m40 it’s too late.
Best of luck with it.

That's unbelievable, my mate just took off the wastegate actuator hose by mistake and ran 25psi. Within 2 hours he blew the head gasket.

I did everything up to specification and yes I used oil on both sides of the bolts.
Everytime I replaced the head gasket I used new coolant with it too.

The only thing I haven't checked is the flatness of the block. Or maybe if I use the "4 notch" gasket, will that prevent this from happening again?

[chaddy]

Your coolant temp sensor could be faulty and may be sending a false reading.

If it isn't too late, I'd like to suggest that you also replace the coolant temperature sensor with a new one.

I have the same 4M40 and when I got it the coolant temp would always go up 1/3 of the gauge which I believe was wrong.

I replaced it right away and it now shows the correct coolant temperature on the gauge which is just below the half range.

When coolant temp sensor is faulty it will send false reading, like mine it was only sending 1/3 temp on the gauge when its actually already 1/2 temp. Or excessively hot when its actually not.

Chances are the engine could already be running hot at 2/3 of the gauge when its only showing 1/3 and mine as the sample.

Just a share from experience.


I agree with Kingmarz on an aftermarket temp gauge, i got one of those digital ones online. Works well!

I did replace the temp sensor 3 months back as the old one died and the glow plugs began to play up. The new sensor fixed everything and even on hot summer days the temp gauge didn't even reach halfway.

I'm suspecting it is much of a compression issue rather than a cooling issue??

[Dongskie2]

I did replace the temp sensor 3 months back as the old one died and the glow plugs began to play up. The new sensor fixed everything and even on hot summer days the temp gauge didn't even reach halfway.

I'm suspecting it is much of a compression issue rather than a cooling issue??

I would agree, but the 4M40 has a pressure relief valve taht opens at 14psi if by accident the wastegate hose has been disconnected.

Unless that pressure relief valve has been tied shut.

[Kingmarz]

There’s no overboost valve on JDM 4m40 with electronic pump. Boosting 25psi without the correct modifications will cause excessive heat with the tiny tf035/td04 turbo so I wouldn’t count out heat causing your mates blown gasket. An EGT gauge would tell if it’s a heat issue or compression issue and is a must on the 4m40. Also not all 4m40’s are the same as they made improvements just about every year it was produced and the last ones with the electronic pump are the strongest and most reliable.

[chaddy]

I would agree, but the 4M40 has a pressure relief valve taht opens at 14psi if by accident the wastegate hose has been disconnected.

Unless that pressure relief valve has been tied shut.

The relief valve does open most of the times when I overtake on freeways and going uphill. Then I just back off the throttle and let the valve close.

Maybe the head gasket brand and head bolts are not good?

[chaddy]

There’s no overboost valve on JDM 4m40 with electronic pump. Boosting 25psi without the correct modifications will cause excessive heat with the tiny tf035/td04 turbo so I wouldn’t count out heat causing your mates blown gasket. An EGT gauge would tell if it’s a heat issue or compression issue and is a must on the 4m40. Also not all 4m40’s are the same as they made improvements just about every year it was produced and the last ones with the electronic pump are the strongest and most reliable.

My mate's one blew because he blocked the relief valve and disconnected the wastegate actuator.
My JDM engine has got a mechanical pump and has got a relief valve as well which opens most of the times under hard acceleration.

I blanked the EGR valve which started leaking (I think comes only on JDM models). Will that causes to blow the head gasket?

[Kingmarz]

Only pre 96 JDM 4m40 has mechanical pump all Oceania models (Australia and NZ new) had mechanical pumps the easiest way to tell is of the speedometer goes up to 180kph or 200kph all JDM vehicles have 180kph and have speed limiters. Blanking EGR will not cause head gasket failure in fact it’s more likely to prevent it. The EGR is known to cause cracked heads in number three cylinder where most of exhaust gasses are directed. Blanking EGR will create about a 1psi boost increase as all exhaust gasses are passing through the exhaust wheel on the turbo and not bypassing it (wasted energy) but 1psi would definitely not cause head gasket failure. Your mates gasket could have been on the way out and the extra boost may have speed up the inevitable. A 4m40 in good condition should be able to boost 30psi before the head starts to lift mine was boosting 23 for two years without issues. Next time you replace gasket use a good quality MLS gasket and quality head bolts or use old original Mitsubishi ones and torque the bolts down another 45degrees as there’s no harm doing that as long as it’s in proper sequence.

[chaddy]

Only pre 96 JDM 4m40 has mechanical pump all Oceania models (Australia and NZ new) had mechanical pumps the easiest way to tell is of the speedometer goes up to 180kph or 200kph all JDM vehicles have 180kph and have speed limiters. Blanking EGR will not cause head gasket failure in fact it’s more likely to prevent it. The EGR is known to cause cracked heads in number three cylinder where most of exhaust gasses are directed. Blanking EGR will create about a 1psi boost increase as all exhaust gasses are passing through the exhaust wheel on the turbo and not bypassing it (wasted energy) but 1psi would definitely not cause head gasket failure. Your mates gasket could have been on the way out and the extra boost may have speed up the inevitable. A 4m40 in good condition should be able to boost 30psi before the head starts to lift mine was boosting 23 for two years without issues. Next time you replace gasket use a good quality MLS gasket and quality head bolts or use old original Mitsubishi ones and torque the bolts down another 45degrees as there’s no harm doing that as long as it’s in proper sequence.

Thanks for this information. I used the "Permaseal" gasket and the head bolts bought from Bursons. Do you know a better brand and a place to buy them?

Shall I go to the thickets (4 notch) head gasket this time and will that make a difference?