Probably need to replace cylinder head?

[glenn]

If you are having all the work done to replace the head gasket - replace the head. These heads do seem to have an expiry date. With exceptions, it is almost always the head anyway. When I did mine a couple weeks ago, I replaced everything - complete new head, belts, waterpump, tensioners, gaskets, thermostat, etc - I already had a new rad. Bill came to $3000, but now I have some piece of mind again.

[Jedidiahwiebe]

From What I've heard A GOOD experienced head repair shop guy can tell if there is a crack or not. If not there's some electrochemical test they can do which shows even microscopic cracks. Though it is quite likely that you do have a cracked head, I think it would be overkill to replace the head if it is only warped not cracked (like mine was) I admittedly am a total amateur, but the suggestion that a block of cast aluminium would have an 'expiry date' seems... well a little far fetched for my worldview. Shouldn't it last as long as the rest of your van provided you didn't overheat it? That being said. Do get an EGT in there right away, to help you prevent overheating and ruining your new cyl head!
TLDR: I'm happy with my old head. Same symptoms as your van, just needed the head decked and I put 'er back on. Runs just fine 20,000k later.

[glenn]

When I say that heads have a shelf life, I'm referring to the fatigue that occurs within a metal casting primarily during heating and cooling cycles. It has been observed that minute casting defects have a detrimental effect on fatigue life by shortening not only the crack propagation period, but also the crack initiation period. Experimenters do not study IF a crack will occur, but after how much fatigue.

Under normal operating conditions, minute defects within a cast aluminum head are subject to fatigue - from heating/cooling cycles, differential stresses between the aluminum head and cast iron block, and from inherent design weaknesses, (like the well documented weak spot at cylinder #3 on L300’s). Over time these stresses work to increase the defect size of the minute defects until they reach a critical defect size and crack initiation occurs. This critical size for initiation may very well, and often does, occur during an overheating event - but it could still occur, albeit more gradually, under normal use.

[Jedidiahwiebe]

Extremely interesting. Makes sense, but I'd have never thought of it myself. Thank you for the education Glenn!

[Jedidiahwiebe]

An update. I didn't replace the timing belts when I did the head job back in 2011. (I just had the head decked - not replaced). Then early this summer the balancer belt failed and was run over by the main timing belt causing interference and pistons hitting valves etc. I replaced broken rocker arm and camshaft hold downs as well as pulled the head to check the valves... which were all straight as an arrow.
I put a straightedge on the head at that time and although there was some warp to it, it still was within the books tolerances.

Then about a month later it started overheating again with the same exact symptoms as from the beginning of this thread. Thought it was to do with the cracked radiator. Suppose that might have been the cause. Got that fixed, tried a new rad cap. Nope. So I guess I'll need to rip the head off for a third time and investigate.

How many times can you deck a head? I noticed that in the manual it says zero times. Is the opinion these days that it is better to invest in a new head... than to deck it?

There are various different heads on offer out there at different price points. Does anyone have any tips on how to know which are the 'good ones'?

[Big-Bird]

Did you check your radiator hoses and heater hoses for signs of weakness? Do they feel spongy or broken inside? A crack woud manifest as a fold or bulge depeding on how severe the damage was.

Did you drain the trapped air from the system when you refilled the coolant? The L400 has an airbleeder line at the firewall near the freash air intake for the cabin HVAC system..not sure of what the L300 has. Don't rely on the expansion tank to capture trapped air.

Have you looked at the tops of the cooling fins on the radiator through the Rad Cap opening? Is there evidence of crud/dirt at the flute tops?


Do you have cooling fin damage that might restrict airflow through the radiator?




Are the fans working properly? Mechanical and or Electric.

Is your tranny running hot? Any additional heat load from your tranny or your A/C system for that matter would incur additional demands on your engine's ability to keep at proper operating temperatures.

What about the thermostat and/or water pump? Are these working properly?

It not unheard of for a thermostat to get jammed in a closed position and cause havoc. If you pulled it and tossed into boiling water with a thermometer you would know what temperature its actually opening at and if its correct for your Mitsu van.

[Jedidiahwiebe]

Don't know how to bleed the air out, but veggie system heat exchangers are working good, so there is no air lock there. Where else can airlock occur? Inside the head? That would be poor design.

All hoses are new in cooling system. No cracks. Radiator rebuilt. Only use distilled water, no lime deposits. Water pump 40,000km old bought from cca. Thermostat is three years old. I believe it works since the engine temp needle jumps up abruptly as usual when warming up the vehicle. Also rad hose suddenly warms up also as if the thermostat is opening proper.

Only symptom is coolant being blown out into the overflow tank. I can drive to town and back with no problems, or even long trips as long as I work her real gently and keep the heater on full blast. (even going up that big ass hill on the coquihalla... but in second gear. Runs hotter than usual though going up long hills)

Tranny might run hot. Dunno. It's always warm to the touch. Its standard not auto.

Fan's good, I think the fan clutch works too.

Anybody know the answer to the question: Can an l300 head even be decked/planed? The manual says 'no'.

[Big-Bird]

Most good quality aluminum heads can be decked once. There are also thicker head gaskets that can sometimes be purchased to obtain the proper valve to piston clearance but that would work for chevy 350 and that sort of thing.....not 1000% sure for the 2.5L

But why it overheats in the first place needs to be addressed or it could happen again.

The air bubbles get trapped in various places and it doesn't take much trapped air for an overheat condition to develop. Done it on my Nissan 3.3L and my gas Mitsu Challenger with the 2.6L in it and I had decked that head once. Mitsu's 2.6 Gas unit is very similar to the 2.5TD in the Delica in its design.

The factory manual for the L300 states if the radiator clutch fan can be moved with light finger pressure the clutch fan is faulty and overheating may result. Also of the clutch fan is low on (oil)fluid it will not be able to spin at the same speed as the pulley its attached to. There is a flat bi-metal wire coil inside the clutch fan that expands and contracts with temperature...its what causes the engagment of the plastic fan...they can break or just get weak and this would also inhibit effective cooling.

In the event anyone else reads the post or has a similar issue this might be of use.


The fact the thermostat is 3 yrs old would be enough for me to check its operation....granted most thermostats are designed to fail in the open position but if it opens too late this would affect proper cooling capability. There are different temp ranges available and even Mardy from Amazing Auto pointed out there have been crossover issues with Pajero Thermostats being stuck in Delicas only to see the Deli overheat...seems Pajero's run hotter and have a thicker radiator compared to a Delica with the same engine.

Here's the section I read through on the L300 cooling system.

http://www.delica.ca/manuals/L-300%20Ma ... ystems.pdf

[Jedidiahwiebe]

Great post Big Bird! That vid is so helpful! Now.. would you say that the fan should move with light finger pressure when it's hot? Or when it's cold? My understanding is that it freewheels when cold. Then locks up when hot yea?

The reason that I think is responsible for the most recent head warpage/crack/gasket failure whatever it is.. is that the top tank of the radiator cracked and was leaking badly. Then overheatage. I simply had no idea how bad it was to run around with a radiator with cracks that prevents the system from pressurizing properly.

I'm just grown up kid who took shop class in high school. Most of what I know about mechanics was learned from this forum.

[Big-Bird]

Check it when the engine is cold, the tech in the video demonstrates the difference of a damaged clutch unit vs new. You should feel resistance when you try to turn that fan.

When did it overheat...when doing 50 kph or less around town or at higher speeds?
Around town the fan would be needed due to low air flow rates...at highway speeds the air flow is usually adequate to keep things cool and the clutch fan will barely engage....but when you slow down the again the air flow drops and the fan needs to start working or temps climb fast.

If your engine was overheating at highway speeds I would focus my attention on air entrapment and the thermostat....specifically the temp range of the thermostat and if its right per the manual and if it opens at the right temp by doing a water boil test with a thermometer to verify actual water temp.


I was a mechanic for several years...although I left the trade for greener pastures I am still constantly reading up on technical manuals for the vehicles I have owned over the years just to keep the skills fresh!