Newbie Questions

beerthirty

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Snagged a 1991 M998 soft top recently. Was wondering how to tell what engine and transmission is in it. On the TM it shows various types and outside of wrecking them every so often in the military I never really did the mechanic shit with them. I used google and searched on here but outside of the TM which lists multiple types I am a bit confused on which one I have. I am looking at swapping all Fluids & Filters. Also if anyone has a preference or recommendation on types of fluids by brand etc throw em down. I live in Iowa so it'll get heat and cold.

thanks,
 

Coug

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Transmission is easy, look at the shifter. Will either have a park position or not. Park means 4 speed.
Engine you should pull the doghouse and look at the oil pump/tach drive.

09  HMMWV 6.2L Engine_Page_1


09  HMMWV 6.2L Engine_Page_2

.
 

Coug

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As for what oil to use, any good quality 15W40 will do.
Some people argue against synthetic claiming their stuff leaked after using it, but it has better protection than conventional does, especially for extreme weather.

As for filters, this list/ranking is pretty comprehensive.
 

beerthirty

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iowa
Transmission is easy, look at the shifter. Will either have a park position or not. Park means 4 speed.
Engine you should pull the doghouse and look at the oil pump/tach drive.

09  HMMWV 6.2L Engine_Page_1


09  HMMWV 6.2L Engine_Page_2

.
Assume that circle thing is the doghouse assembly.
 

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beerthirty

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iowa
Also. Looking into adding some instrument gauges onto a radio mount when it comes in. Anyone ever add a oil temp, better tran temp and other gauges before?
 

Coug

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Assuming I'm correct. This is the 6.5 detuned.
Overhauled in 2010 std bore, st mains & rods according to engine plate.

With a 6.5 detuned I'm assuming there's possibilities of adding hp etc like a turbo?
while physically possible, it's really not cost effective if you are trying to do it properly. Requires a bunch of new parts, lots of labor, and in the end most people will recommend that you just install a used 6.5 turbo motor and 4 speed transmission to install instead.

These aren't designed to be drag racers. The stock engine will get you to where you need to go, along with the 3 speed, but it won't get you there fast. You should keep your sustained speeds to 55mph or less, though some will say 60 with the 6.5 (though that's mostly the GEP block, not the GM), due to heat soak issues with the GM blocks where you will cook the back 2 cylinders if you keep your speeds up too long.
 

beerthirty

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while physically possible, it's really not cost effective if you are trying to do it properly. Requires a bunch of new parts, lots of labor, and in the end most people will recommend that you just install a used 6.5 turbo motor and 4 speed transmission to install instead.

These aren't designed to be drag racers. The stock engine will get you to where you need to go, along with the 3 speed, but it won't get you there fast. You should keep your sustained speeds to 55mph or less, though some will say 60 with the 6.5 (though that's mostly the GEP block, not the GM), due to heat soak issues with the GM blocks where you will cook the back 2 cylinders if you keep your speeds up too long.
Pretty much drive at 45-50 on the highways.

There is a odd tire lean on the back wheels. They lean inwards from top and out on the bottom a bit on both sides. Haven't had a chance to see if shimmed.

As for labor, usually its myself tearing into shit. My first diesel that I rebuilt this year was a 99 7.3L that was rebuilt from the frame up. Probably took 10x the hours a shop would do.

Is there a way to get rid of or slow the heat soak on the 6.5L? Assuming its probably a internal issue. So moving PMD or other parts + putting on a large heat shrink shroud around the engine itself probably won't prevent it?
 

Coug

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Pretty much drive at 45-50 on the highways.

There is a odd tire lean on the back wheels. They lean inwards from top and out on the bottom a bit on both sides. Haven't had a chance to see if shimmed.

As for labor, usually its myself tearing into shit. My first diesel that I rebuilt this year was a 99 7.3L that was rebuilt from the frame up. Probably took 10x the hours a shop would do.

Is there a way to get rid of or slow the heat soak on the 6.5L? Assuming its probably a internal issue. So moving PMD or other parts + putting on a large heat shrink shroud around the engine itself probably won't prevent it?
No way that I know of to get rid of it.
When GM stopped manufacturing the blocks and Navistar took over (General Engine Products, or GEP for short) they changed the metallurgy of the block and I believe changed the design a little in order to take care of those issues.
Now that we have determined you have a 6.5, you'll want to look behind the left cylinder head on the block to figure out casting date. If it's after 2000, then it's going to be a GEP block.
Once again, take the doghouse cover off, and then sit in the passenger seat. Look for a small flat area on the block just behind the passenger side cylinder head, then post the numbers here and we can tell you what it means. If you are lucky they put a rebuilt GEP block in instead of the GM.
 

papakb

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The tires leaning in at the bottom is completely normal. When there's some load in the back end it will straighten out. Mine did it until I dropped an ambulance body onto the chassis, then the wheels were verticle. An unloaded truck is riding at the top of the suspension and will be a harsher ride than when it's partially or fully loaded. If you want the ride to smooth out, throw a couple of heavy weights in the back to preload the suspension.
 
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osteo16

Active member
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Evansville, IN
I think Paradox By Design has a kit to move coolant to back of engine block to help with cooling it.. Fairly cheap but not sure of results personally..

Take a peak..

Ocho
 

beerthirty

New member
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Location
iowa
I think Paradox By Design has a kit to move coolant to back of engine block to help with cooling it.. Fairly cheap but not sure of results personally..

Take a peak..

Ocho
Will do. I got a friend who runs drag who's going to look at it this weekend and see if we can't fab up a heat sink or a system to move the heat efficiently. Using the soft top as a daily driver and trying to keep as much original as i can. Lol not exactly the best idea
 

osteo16

Active member
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85
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Location
Evansville, IN
Will do. I got a friend who runs drag who's going to look at it this weekend and see if we can't fab up a heat sink or a system to move the heat efficiently. Using the soft top as a daily driver and trying to keep as much original as i can. Lol not exactly the best idea
HAve at it... that’s what they are for.. and if you come up with any “ Mods”, please share.. we are all usually trying to improve or upgrade our rigs 🤘🏼
 

beerthirty

New member
15
1
3
Location
iowa
No way that I know of to get rid of it.
When GM stopped manufacturing the blocks and Navistar took over (General Engine Products, or GEP for short) they changed the metallurgy of the block and I believe changed the design a little in order to take care of those issues.
Now that we have determined you have a 6.5, you'll want to look behind the left cylinder head on the block to figure out casting date. If it's after 2000, then it's going to be a GEP block.
Once again, take the doghouse cover off, and then sit in the passenger seat. Look for a small flat area on the block just behind the passenger side cylinder head, then post the numbers here and we can tell you what it means. If you are lucky they put a rebuilt GEP block in instead of the GM.
Assuming you mean the smaller work order plate in picture?
The larger one says serial# FY10 6664-141 OR 6669-141

Small plate in photo says
Work order:B917709
NSN:2815-01-439-6664
Serial#6664-141
Repair standard NMWR
 

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