"Evaluating a Vintage Diesel"

[TurboTahoe]

Hi guys,

I ran across a couple of articles which even mention the 6.2 as a nice older diesel truck, and then proceeds to give you all kinds of advice on how to do qualitative testing on its condition. What do you guys think of the advice?

http://www.automedia.com/Vintage_Diesel_Car_Care,_Part_1/ccr20060101d1/1

http://www.automedia.com/Vintage_Diesel_Car_Care,_Part_2/ccr20060201d2/1

Is it accurate? Their description of blow-by seems reasonable.

The one I enjoyed was the 'informal compression test'.

-Rob

 

[Woody35]

sorry i cant hear the differences in compression when im cranking my truck. and the example was a 1981 benz diesel which after 28 years should of lost a little compression. other than that i guess it was a okay article

 

[Missy Good Wench]

Here is how I evaluate one of these beasts.

First (After hood is open)
Check coolant level, oil level etc.
Look under the rig for signs of major leaks of oil coolant fuel etc.

Spin the engine without allowing the glow plugs to heat. The starter sound should be even with an even za za za za za za za za za sound

An uneven sound of za za za zzzzzzzzzz za za za is an indicator of a low hole.

Once you have heard this sound you wull never forget it.

If you wonder what it sounds like, remove one glow plug from your diesel (H Front is easy )

Unhook the power to the OP or unplug the PMD and then spin the engine. aside from the swoosh of air from the glow plug you will right quick notice the different sound that things make.

OK

If the thing spins evenly, go for a glow cycle and see how it starts.

Good clean crisp start with no great amount of smoke is a good indicator that things are good in the injection system (compression too)

Some missing and white to bluish smoke that clears reasonably quick could indicate some glow plugs not working.

A longer time with missing and smoke can indicate that the injectors are tired and in need of replacement.

Once the engine has run for about 30 seconds there should not be any smoke at all.
Smoke at this point is indicative of issues with injectors or several other things.

A smooth running engine that still exhibits smoke at idle likely needs a set of injectors.

OK
Its running and seems smooth enough and has no smoke.

Look at the oil pressure.

45 or so is normal for a factory setup 6.2/6.5 and will drop off some when things warm up.

40 PSI runnin at speed and Idle at 20 or so.

While the beast is warming up feel the upper radiator hose, it should remain flacid (Soft and squishy) while the engine warms up.

A quick pressurizing of the cooling system followed by coolant puking over the overflow is an idicator of a blown head gasket, cracked head, cracked cylinder wall or ??? that allows compression into the cooling system.

OK
Engine warming up nicely and no issues. Take the rig for a romp and bring the engine to full operating temperature.

The top Radiator hose should have some pressure but not HARD and no coolant puking from the tank vent.

Engine should idle smooth and even with a nice even diesel cackle to it.

Take note of oil pressure, it should be steady and not below 20 PSI at Hot idle.

Shut down and let sit a couple minutes. Yank the dip stick and look at the oil, it will likely be black. Notice the level on the stick as well as the texture of the oil.

We are looking for signs of Glycol in the coolant.

A diesel will not always show a milky sludge if it is contaminated. The black soot will cover this up very good at times.

If we are dealing with a turboed engine, remove the air inlet to the turbo and inspect the inlet to the turbo.

Some oil pullover is normal as these engines get lots of miles on them. The turbo can even have a fair amount of sloppy residue just as long as its not dripping and totally juicey with oil.

While theair inlet is off, (Engine shut down) spin the turbo impeller, it should spin freely and not show signs of having been rubbing the housing.

Some slight radial play is normal but the shaft should not move in and out that you can feel much.

Look for signs of oil leakage from the turbo cartridge (center section) that is leaking down on the outside.

Some seepage is normal on any engine with a Buttload of miles.

Now lets look under the rig.

Any large drips that emanate from the bellhousing drain hole or around the filter area.

Again some seepage is very normal with miles and time.

Now

How is the tail pipe when your running down the road, smoking any at cruise speed. A little puff of black under full pedal is normal and depending on how the Pump is set up (DB2) or chipped (DS4) the smoke can be more or less.

The engine should run down the road with plenty of power (tain't no top fueler though)
The engine noise should be a nice even cackle that deminishes some with full throttle and gets a bit sharper under light throttle cruise.

With engine hot, shut down and let sit and heat soak for 15-20 minutes.
Try a restart without allowing the glow cycle to finish. The engine should start right up with very little cranking.

A long crank time hot can indicate a worn out injection pump (Was seen on some late DB2 pumps with high miles)


So now lets look at the accessories up top. Is there any undo noise, rattles or other obnoxious noises coming from the water pump, vacuum pump (later 6.5 stuff)

Take note of the belt drive, the isolator pulley (Serp drive systems)

This about takes care of as much as you can inspect without digging into the sucker.

If it passes muster this is about all you can do to tell what shape its in.

Now I will say this.
I have done the previously described protocols and drove a rig home only to have a head gasket blow a month later.

There is no way to tell absolutely what shape the thing is in.
To give an example

Bought a High mile Suburban off ebay.
The rig was in SanDiego Cal
Flew to Socal, met the seller, we look the rig over, he starts it up and its running fine.
(1995 2500 Burb 4x4)

Chating for few minutes and getting ready to hand him the check for the ballance owed.
All of a sudden the Burb starts missing, smoking like crazy (smells of diesel fuel and antifreeze) puking coolant out the overflow top hose hard as a rock.


Hmmmmm decided to blow a gasket right there. had this happend 20 minutes later I would have been out on one of SOCALS myriad freeways on my way back to Oregon.


OMG what a mess that would have been.

Cost me a flight to SanDiego then home again. Got all my Money back though for the deposit on the rig.

Not to try and scare but simply to point out that these things with a Buttload of miles can give up even though they seem fine.

Anything over 200K miles should be treated with the idea that it will need something in the way of work.

Hope this helps to scope out and purchase a used diesel.


best

MGW

 

[TurboTahoe]

Robyn! WOW! That is a wonderful, concise, thoughtful, and thorough write-up!

Mods, THIS SHOULD BE A STICKY!

-Rob

 

[Missy Good Wench]

You are very welcome

Missy

 

[GM Guy]

Excellent write-up Missy!

:thumbsup:

 

[Missy Good Wench]

Been down the rough and rocky road of buying used diesel rigs.

If the price is right and the body and interior are sweet then ya can make a mistake and get away with it and not hurt. BUTTTTTTTTTT if ya lookin to get a decent engine, youuuuuus gotta be careful.


MGW