6.2 Diesel Questions

[bmchevy1979]

So I am looking to buy a truck with a 6.2 diesel and a 4 speed I just want to know what should I look for as far as the engine to make sure it is in good shape

[babyJay]

Here's an excerpt I borrowed and saved from a fellow board member (Russel) posted to another thread. Lots of good info here.


"A 6.2L pretty much bolts straight in place of the 350. Here is a quick guide covering the major systems:

Fuel

You'll need to drain your fuel system as best you can, and it'd be a good idea to replace all the rubber hoses with new ones as fuel leaks are a major problem with a diesel engine. Its ok if you've got a little bit of gasoline left in the bottom of your tank, so don't go crazy trying to dry it all up. Just make sure you fill the tank right full with diesel before you try and start it up the first time. You can use the gasoline supply and return lines with a 6.2L diesel engine, as the fuel pump is located in the same place for both. You will need to install a fuel filtration system with a 10 micron filter, factory is to start with a 30 micron then step down to 10 with spin on filters, and a 10 micron block filter later on. Your best bet is probably to grab a Racor spin on system and mount it to the firewall just up and to the passenger side of the engine.

Electrical

Electrical is really easy on a 6.2L diesel. Use the factory 6.2L's harness and plug it straight into your bulkhead connector on the firewall, the pinouts are the same between the diesel harness and a gasser's harness. You will need to drill a small hole in the firewall to install the small diesel interior harness for the glow plug lights, low coolant light and water in fuel light (should you decide to install the bunch) The glow plug light and low coolant light is installed in a small pod that clips into your instrument bezel just above and between the fuel gauge and the speedometer openings. You will need to take the die grinder to your cluster to install it. While the instrument cluster you have will work just fine, you may want to replace your oil pressure gauge with a 80 PSI unit, as the diesel engine will peg your 60 PSI gauge on a cold start. You could also replace the fuel gauge with one that states to use diesel fuel only as well. The choke light is replaced with the low coolant light on a 6.2L diesel truck.

Cooling

A 6.2L is an engine that produces a TON of heat, and needs lots of cooling as a result. The factory 6.2L diesel radiator is a 4 core rad that is a good 6" wider than a gasoline rad is. With minor modiciations you can install the 6.2L diesel rad and rad shroud into your existing core support, or you can choose to buy the core support from your diesel donor truck (if you buy one). Make sure you grab the diesel cooling fan, as it is significantly bigger than a gasoline engine's. These diesel engines also utilize an engine oil cooler to help keep them just that much cooler. You can bypass the cooler by installing a loop between the two ports above the oil filter, but you must maintain flow through those ports to maintain proper oil pressure. I personally installed a large B&M plate cooler designed for an automatic transmission and hooked it up using hydraulic hoses and fittings.

Other Mechanical Considerations

Exhaust should bolt straight up between your 350 and your 6.2L, but you may want to change your exhaust to something free flowing with straight through mufflers. The more air you can move through your diesel engine, the more power it will produce. No diesel engine naturally produces any vaccum, so you may need to install a vaccum pump to operate any accessories that need as much. If you have an automatic transmission, you will need to change out it's govenor and install a very low stall diesel torque converter for it to work properly. There is a vaccum regulator found on the military trucks with the TH400 to operate the vaccum modulator found on both it and the TH350, but they are quite rare and normally don't work properly anyways. Your best bet is either the 700r4, or a manual transmission. I personally chose to run an NV4500 5 speed manual transmission behind mine.

A few notes on the 6.2L, and what to look for when purchasing one

A 6.2L diesel is a light duty naturally aspirated (from the factory) engine with 23.5:1 compression. They produce about 130 hp / 240 ft lbs in the C code (with EGR) intake / injection pump, and about 150 / 300 ft lbs hp in the J code configuration. Both engines are very capable of over 20 mpg, but neither is a real power house. If you are looking for an engine that you want to hot rod around in, or tow heavy loads, then you'd look elsewhere for a medium to heavy duty diesel engine. Both the C and J code engines are very accepting of a turbocharger, and will produce over 200 horse and nearly 400 ft lbs of torque. Max boost levels is between 7 - 10 PSI, and it will make the engine perform similar to, if not better than a TBI 350 from the late 80s / early 90s while still acheving better than 20 mpg.

When you are shopping for one of these engines, there are a few things to look for. First is for smoke. These engines should not produce any smoke at idle, and only a very light black haze on a heavy acceleration. A small amount of white / blue smoke on startup for a few seconds is acceptable (one or two cylinders may not be firing). The second is for blowby. Pull out the dip stick, or the oil filler cap and take a look. A small bit of steam coming from the engine is normal, and is dealt with by the CDR canister, but you should not have a huge ton of steam (shouldn't look like a tea pot at full boil), and it should not be sucking your finger up against either opening. Pulsating is normal however. A third consideration is the sound of the engine. It should have a healthy clack about it, but it should not be ticking or knocking. It is a bit difficult to tell the difference sometimes when you are new to these engines, but try your best! The fourth thing to check is the harmonic balancer. These engines heavily rely on them being in good shape, and there must not be any swollen rubber, missing chunks, cracks or a spun outer ring. The last thing to check, but isn't always possible, is for cracks in the main webbings. These engines are notorious for cracking down there, the best solution is to use a lock and stitch procedure, combined with a main girdle. Small cracks are acceptable here and there, but cracks that run all the way down the main bolt threads are no good."

[babyJay]

guess i forgot to mention the last paragraph is the info you were looking for.

[jitteryguy]

I work on a lotta HMMWV's with 6.2 & 6.5's , they are a tough engine, take more abuse than they get credit for (amagine upset'n a neighbor kid then tell'n he has to drive your truck in the desert for 6 to 12 month's, it will be abused). remember the oil will always be black, even soon as it start's after an oil change, nature of an old deisel. follow the last couple of BabyJay's post and you should be good.

I recently bought one of my son's a '84 with a 6.2/4speed, he's get'n bought 25MPG. so if it run's good I'd jump on it.

[Altec]

Originally Posted by jitteryguy

I recently bought one of my son's a '84 with a 6.2/4speed, he's get'n bought 25MPG. so if it run's good I'd jump on it.

2WD, or 4WD? Gears?

[jitteryguy]

Originally Posted by Altec

2WD, or 4WD? Gears?

I aint sure bout the gear'n,I assume 3.73 but honestly dont know. it's 4 wheel drive with lock out hub's and 31" tire's on stock ralley's

[bmchevy1979]

Cool good to know thanks for all the info

[Altec]

Originally Posted by jitteryguy

I aint sure bout the gear'n,I assume 3.73 but honestly dont know. it's 4 wheel drive with lock out hub's and 31" tire's on stock ralley's

Might be 3.08's if it is a 4-speed.

Always good to hear about good mileage on the K's. Can't wait to get my 6.5NA in fighting shape...

bmchevy1979- Good luck with your future purchase! Babyjay's post is dead on for your hunt!

[bmchevy1979]

Thanks guys for the Info. And I have another question will all of the top end components from a 6.5 (heads and up) bolt directly onto the 6.2 becuase if every thing goes through I might want to add a turbo or other power adding parts.

[Altec]

I believe the HMMWV as it's own set of heads that use a special intake. Other then that all of the major components are bolt on. Taking the turbo charger from a 6.5 and putting it on a 6.2 is a bolt on deal.

If you do a turbo swap you can keep your heads though. The only real difference between 6.5, and 6.2 heads is the precup size. Which everyone I have talked to that swapped to the larger 6.5 ones saw no real power gains.

Just remember to be careful with the girl. Before my 6.5 goes in my truck it is getting A LOT of work to beef it up. Including head studs, custom girdle, filling the water jackets, head studs, and a few other things. Then again, I'm shooting for at least 350HP.