Need help with my M998 Heater

[kcpstudio]

Hi guys... going to try and repost this. I have a 4 man soft top M998. I'm from PA and winters can be so so. As you know, the heater blows! Yes pun. Anyway, I'm wondering if anyone ever upgraded your truck's heater to something that actually worked. I'm looking at a unit which could fit in the current OEM area. It's coolant lines are in the correct spot as well. It claims to be 60,000 BTU (543 BTU at 8 amps). It's a 12 Volt system as well. I have the 200 amp dual voltage amp in my truck in case that matters. Also, it is a dual fan high output set up it claims.

Anyway, I don't want to run a fuel heater or straight electric. I'm hoping some of you can shed some help on this.

Thanks

 

[155mm]

IMO, I think an H82 heater would fit perfectly.

 

[ryanruck]

I installed an MRAP heater in mine and did a detailed post on it.

It sounds a lot like the one you're describing but it's a 24v unit.

Details here.

Keeps the truck nice and toasty!

 

[kcpstudio]

ryanruck YES! That's the unit. Thanks for the link brother!

Thanks gents!

 

[Action]

In my slantback, i put in an early H1 core. It was bigger but still fit in the humvee box.

 

[kcpstudio]

My fiancé and I drove up to see her family in Michigan during the winter. That's when I knew that was the first and last year I was going to deal with that kind of cold in the truck. I ordered the heating unit tonight. As soon as that gets here, I'll take some pics and document so I can pay forward the help.

 

[DCIV]

Anyone else do this? Is there a way to keep the factory wiring switch? Any other ideas for the extra heat outlet?

 

[kcpstudio]

@DCIV

yes... if you can wait a little, I’m working on it now. I have installed 24 volt heated glass in my truck and getting ready to work on the heater. What I did was come off the outlet to the heater valve and instead of going into the factory heater core, i’m running into the new heater core. Then the outlet to my new heater core runs into the inlet to the old heater core. Then last.... run from the outlet to the old heater core back to the engine. This way I keep the original fan and heater core mainly for defrosting and the new core strictly for heat. I’m running a similar rotary switch to the one that was recommended to me. The rotary is mounted near the original toggle switch. Once completed, I leave the factory witing alone. I’m using factory wire “Ts” to tap into power. Again, once I’m done I’ll post pics of everything.

Cheers

 

[kcpstudio]

Success! Gentleman, I have great news for all you HMMWV owners that are tired of the poor heat these vehicles put out. I have completed my heater upgrade and have some initial test results. I'm going to create a new thread and post all the progress pics. I'm also considering on putting a very nice complete kit upgrade together if you guys want to purchase and upgrade your trucks. I have a 1989 M998 4 man soft top. It has a 6.5L GEP engine. This has a total reset with extremely low miles on it. However, with that said.... the heat in this thing was just as I remembered during my time in the service. It sucked!

So, I set out to come up with a solution but I wanted to keep the overall military look. After a couple months of researching on and off, I found a 60,000 BTU heater unit. I did not want to replace the factory heater unit... so I came up with a design which maintains everything and just add the new unit. I set it up as the primary heater core and the original as an aux unit. I put together a set of radio trays to house the new unit. I also have a separate switch to operate the new blower.

Okay.... so I did two tests today. The first test I had the truck sitting outside all morning so I could start with a cold truck. The outside temp was 47 degrees. I'm using a temp meter with sensor to conduct my tests. I started the truck and allowed it to come up to complete operating temp with no heaters running. At this point, I started the new heater only and kept it on the medium blower setting. About 7 minutes later, I was showing 98 degrees F within the center of the vehicle at center height. At both rear corners areas against the rear seats, I'm showing 82 degrees F. Now, here's the best part. In both front drivers side and passenger areas at chest height, I'm showing 119 degrees F. Yup.... 119 degrees F. I then shut the truck off and let it sit all day and conducted the second test at 9 pm tonight.

Current temp at 9 pm was 35 degrees F. As before, I started the truck and let it come up to full operating temp. I had both heaters shut off while coming up to operating temps. Once it was ready, I turned on the new heater and left it on the medium blower setting. Roughly 7 minutes later, I ran the same tests at the same areas. And as I was hoping.... I got the same results.

Today I ordered some insulation material and tan fabric so I can make some insulated door panels which will Velcro in. One other huge thing I did was spend a lot of time adjusting doors. One of the things I learned overseas was how to adjust doors to seal them up big time. Yes, you can seal them up very well and I'll show you guys how to do that. Like I said, I'm going to star a new thread and post everything. But I'm also going to post youtube videos showing everything in detail. And as stated, I'm looking at doing complete kits if there is a demand. When I'm ready to post the new thread, I'll let you guys know here.

 

[kcpstudio]

Oh.... I almost forgot to mention an important note. My fan clutch has not been working and the fan is running all the time. Even with that issue, I'm running hot temps in the cabin

 

[Action]

Oh.... I almost forgot to mention an important note. My fan clutch has not been working and the fan is running all the time. Even with that issue, I'm running hot temps in the cabin

Do you think the original heater would have worked fine if you had fixed the fan and checked the hoses for dryrot holes? Also check the valve by the overflow tank. They can freeze in place and not open or close completely...

 

[DatGuyC]

+1 I have the stock heater on a 6.2 and it puts out plenty of heat when the truck is warm. It was low 40's outside and I was wearing shorts and a sweatshirt going to/from the gym and I had to put the heater on the low setting because the truck got so warm.

 

[1 Patriot-of-many]

Do you think the original heater would have worked fine if you had fixed the fan and checked the hoses for dryrot holes? Also check the valve by the overflow tank. They can freeze in place and not open or close completely...

Not in MN......The heater must be made for Saudi Arabia!

 

[kcpstudio]

No, no way the stock heater will put out enough even if the fan clutch was fixed. Everything else I already tested and works. I tested the clutch to get it to release and it’s bad. I have a replacement. I just haven’t installed it yet. Once that’s installed, the heat output should be even better with the new system.

Even with a bad fan clutch, I’m still getting up above 210 degrees at idle and that more than enough for testing the original heater core. Also, my original core is fairly new and not clogged.

I have no idea how anyone is getting awesome heat with a stock heater in these trucks... at least the older M998s. The BTU output is just not enough. I was in the military for 14 years and road in quite a few and they all sucked. Plus, your location is important as well. It may fly in the lower states, but up here in the northern states, it sucks. So, you gents are lucky in the lower states.

 

[kcpstudio]

If you got a truck with a heater running like that.... you are one of the few and lucky... and I hate you for it.

 

[kcpstudio]

Would like to give a shout out to Ryanruck for his details on his truck’s heater setup. I was on the fence about purchasing the new heater unit I have and once he told me about his success and what he did, I felt better. His detailed post was very informative.

So, a huge thank you to RyanRuck! Much appreciated, brother!

 

[kcpstudio]

I’ll be posting soon. I have come up with a kit. It keeps all the factory parts but adds a primary heater. All the additional wiring and switch assembly looks factory as well. I machined a new switch plate for the additional switch. Initial tests are truly amazing. With outside temps in the mid 30s, the heat it’s producing in the driver and passenger areas are around 119 degrees F. Center mid truck area is seeing 98 degrees F. And the areas in the corners above the rear seats are seeing 89 degrees F. This is on a medium setting.

I video documented the entire upgrade and im just cleaning up now some of the little details. So, I’ll be making a new thread soon. I’ll be offering kits as well.

 

[DCIV]

What price range you looking at?

 

[kcpstudio]

Working all that out now. There are a few more things I’m doing to finish up. Mainly just “dressing up” everything.

What price range you looking at?

 

[NormB]

Working all that out now. There are a few more things I’m doing to finish up. Mainly just “dressing up” everything.

Looking forward to all this.

Heat I can stand. Don‘t want the extra trouble/hdwr for AC anyway.

Been thinking about adding something like this:



http://www.jegs.com/i/JEGS-Performance-Products/555/70611/10002/-1

to the back seat area (just forward of the bulkhead), trying to figure out how to get a couple of straight pieces of 1/2“ ID copper tubing (or PEX) plumbed under the tunnel).

Something to mull over anyway. Throw into the mix.