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-   -   Myths and fairy tails about the VM TD (http://www.ausjeepoffroad.com/forum/showthread.php?t=96380)

Deezelweazel 31-05-2010 07:51 PM

Myths and fairy tails about the VM TD
 

After reading some myths, and fairy tails about the reliability aboiut the VM 2.5 Diesel engine and seeing people spending hard earned money on gadgets that are virtually worthless I think it's time for some basic knowledge.

If you are the person thinking knowing all wisdom about this engine stop reading...:rolleyes:

After doing a bit research (the last 2 years), talking to the biggest engine rebuilding manufacturers and discuss the abilities with internal combustion engineers I found several reason leading to engine fail.

It all started with chasing failed engine heads and searching for the causes.

after finding out that most people are not informed how to behave with a "modern" Diesel engine I think we should start here.

1) This engine is extreme cold start sensitive!

Construction of this engine is unique and advanced at its time. The crank bearings are embedded in a circular alloy case.

http://up.picr.de/4471816.jpg

Due to the reason that alloy and iron have different heat expansion rates they move until they reached proper operating temperatures!

The same goes for the single heads. The heads move until proper clamping force is reached by operating temperatures. If you hit the pedal in this time frame you ask for trouble. Reaching water op temps is no indicator for operating temps. Oil temperature is the proper indicator for that! If you drive without obeying this- blown head gaskets...

The oil pump is located in the front of the engine the suction head is in the rear in the oil sump, of course. Most of you don't recognize the time which is needed to built up oil presure- which is long compared to other engines( have in mind we talk about seconds- but for bearings this is long!)
Add a cheap oil filter with a faulty or cheap or in the worst case without anti drain back valve and you spin the engine bearings dry.

Idle the engine until proper oil pressure is reached!


Bores wear at an alarming rate,as do the pistons /wedge compression rings, if the oil isn't changed regularly and the engine driven 'hard'.

Camshafts wear, due to the high loads,2:1 rocker ratio, the rocker arms are the same as well as the rocker shafts.

The bottom end however is nearly bomb proof, providing the front main bearing doesn't turn in its bore.

All heads need to be bolted down on a jig and done at the same time rather than each individual head as is commonly done. Lining them up to the gasket and the block is extremly important as partially covering holes leads to failure.

If you can't afford a good oil and filter and a frequent change within the interval, do not drive a Diesel.

2) The cooling system

Head cracks develop between the valves and at the side of the heads were are no water cooling gallerys.
The engine is tilted upwards towards the front that causes the air being caught in the front of the heads, causing hot spots.
Engine coolant must be refilled while the rear of the Jeep is on a ramp or you have access on a vaccum coolant refill. Otherwise you ask for trouble.

Stop playing around with electric fans- trucks and semis around the world go with visco fans for a reason- huge airflow and being effective. Now you think an electric fan is the solution?
I've seen electric fans being used without a proper build fan shroud.
Do you know what a laminar short is?
So you play in the mud, do you? Did you ever recognized that the front of the visco fan is actuated by a temperature sensitive spring?
Cover that spring with mud and dirt and wonder why it doesn't work right?
A Brass brush works wonder on your fan front- just give it a try.

Stop your cheap tries to improve cooling. Your Jeeps are at least ten years old. You have to bite the expensive apple and to replace that cooling system.
I would call myself extremly careful with the cooling system.
But I got a tablespoon of dirt out of the engine,while cleaning the heater core.
I found a layer of thin grease inside the engine which required aggressive cleaning. Voila engine temps respond quicker to fan activity.

If you can't afford this- don't buy a Diesel!

Do you know why the factory radiator is made of brass / copper and not of alloy? Because of the much better heat transfer of copper. That makes the radiator expensive, of course.

To be continued...,

but I'm keen to listen to response and thoughts so far.
Please don't tell me your electric fan is so good-it's boring to listen to that.
It has a reason why every serious military truck uses the visco fan.
You can have the biggest airflow which is useless if you have no heat transfer or restricted flow...

Jimmyb 31-05-2010 08:06 PM

Good read, well worth sticky for TD drivers of any Jeep.

Yom 31-05-2010 08:12 PM

Excellent post.

No problem with the machinery, it is always user error.

Antiferret 31-05-2010 09:15 PM

all the above reasons why the VM makes a great boat anchor/ i mean engine:rolleyes:

there must be a few things to spend money on to better the useability of these things. Unfortunately all the above displays is the motors italian heritage.
how come they couldn't have maybe included a wally factor like the patrol 4.2 diesels?

Kudos on the oil filter etc.
i am not slagging xj diesels, i sought one out, but compared to the 4.0 pet.......

i know which one will be more likely to get me home

Gildo 31-05-2010 10:30 PM

Yeah, all of the details above are why anyone who wants to spend time driving and enjoying their jeep not mainaining and babying a temperamental piece of Italian engineering should NEVER consider a diesel XJ.
Stick with the 4.Oh!

amlav 31-05-2010 10:36 PM

I totaly agree with Deezelweazel.
If it comes to think of it a car is designed by hundreds of engineers and thay
pretty much know what is needed to make a car as reliable as possible to be
able to put it on the market.
Cheers,
Andrei

Deezelweazel 31-05-2010 10:41 PM

Hehehe, the complete story is to proof the reliability, if you bite the (expensive) forbidden fruit.
The Diesels are nice, if you do your homework. If not, they will turn into a neverending nightmare and construction site( ...or a boat anchor, hahaha).

I have invested so much money that I can't simply turn back.
Instead of seeking for solutions to extend engine life, you must seek for causes.

Eliminating causes are the best way.
What do you do when stuck in the mud? Changing back to street tires? No, you upgrade to Boggers!

But to play sucessfully- you have to return to the Diesel roots and know the special needs of a Diesel.

Deezelweazel 31-05-2010 10:50 PM

I'm going to pick on the vintage iron gasser engine layout, when done here.:mrgreen:
By the way, who is telling the old fairy tale about being used as a boat engine? Engine design is not made as a cold running engine. As can be seen on the alloy bearing carrier rings.
This engine was used with great reliability and success in austrian agricultural machines(Reform)under heavy load conditions.
Engine setup is different. Lower charger pressure and different cooling layout with a much lower red zone.

Did anyone recognized the manipulated engine coolant temperature display? It stays locked around 90 to 100- in case of overheating the needle jumps suddenly to the red zone! This is not possible with a linear reading meter.

Persep 01-06-2010 02:16 AM

Read somewhere ages ago that car manufacturers won't fit linear gauges coz they create unrest -- ppl just don't like seeing that needle creep. So they actually forced some poor engineer to deliberately create gauges that act like a indicator light. You might as well have a light on the dash that glows red when there's trouble. (Come to think that's exactly what my old HQ holden did have :D)

Don't know if it's true or not....


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