Coolant/heater issues?

[Ajax MD]

Ok, I drove a plain, 2002 M998 home some 82 miles today. Yay, me.

I have downloaded what I think are the right manuals and I am reading them, but help me understand a few things:

Item 1. There is a statement in one of the manuals that says:

Do not operate heater when ventilation system is on. Damage to heater or injury
to personnel will result.

Does this only apply to ambulances or maybe fuel fired heaters? I'm curious if I was operating the cab heat incorrectly.

Here's the issue: While driving home, just one time, I heard a "Sss sss sss!" and suddenly there was a single, quick burst of steam from the passenger's heater vent.
I immediately pulled over, thinking I blew a hose. Nothing. No leaks, coolant level normal in the expansion tank. Engine temperature steady. I cautiously resumed driving and made it home with no problem. It was as if a relief valve briefly lifted. It never happened again.

Item 2. I understand that the truck has a fan clutch operated by a variety of signals, some electric some not.
While driving, I occasionally heard a rush or roar and felt a very slight bog on the engine. It wasn't all that often, and never lasted for long. I assume this was the engine cooling fan and that this is normal operation? I was pushing 50-55 mph on the highway for extended periods. Air temperature was 50F.

Qualifier: The engine temp gauge consistently indicated 210-220F degrees. Yes, I know this is a bit hot (190F - 230F). I also know that the danged gauges and senders are often faulty and electrical gremlins cause all sorts of erratic readings. BEFORE departing, I performed a cautious pre-trip inspection. All fluids were checked. Although the gauge indicated high, I was able to place my bare hand on all parts of the radiator, rad hoses and expansion tank for extended periods of time without burning myself. Like a jackass, I left my IR temp gun at home. I'll get the engine up to temp and shoot it and report the results.

Overall, the truck performed well. Transmission shifted properly and smoothly, engine had good power and acceleration. Oil pressure always correct. Turn signals a bit glitchy.

Your thoughts are appreciated.

 

[BLK HMMWV]

the cooling fan comes on around 220 ish drops it back down to around 210ish the first time you hear it you have a WTF is that moment. and yes you will feel a lag when it's on

 

[Ajax MD]

Right-O. Seems odd that the truck would run that hot off a 50F degree day... or is it? I was pushing it pretty good. I guess this means the tempo guage is accurate.

 

[Coug]

Sounds like fan is doing it's job properly, and that the temp gauge is close enough.

A lot of these units have issues with the coolant system being gunked up from who knows what happening to them, everything from muddy water being poured in, to incompatible coolants causing chemical reactions.

Big first thing to do is flush the cooling system really well, and if that doesn't help the problem take the radiator and heater core out, and get them professionally cleaned at a radiator shop. Install a new thermostat at the same time since you're already in there. Maybe even a water pump and anything else you think it might need on the front of the engine because it's a lot easier without the cooling stack in the way.

Other option is to find an aftermarket radiator that fits the space and has better cooling characteristics, and replace the heater core with the one from an MRAP as it's rated for about twice the BTU output.

 

[Coug]

The warning in the book you posted doesn't apply to the heater operated from the driver's seat. Most likely for either the ambulance or a comms shelter.

 

[Ajax MD]

@Coug I did squeeze the upper hose and got some coolant to burp into the tank but I felt that there should be more.
I agree that the thermostat might be gunked up. I'll perform a coolant flush and go from there.

Obviously, the first steps in new ownership should be a total fluid purge and replacement with filters anyway.

 

[papakb]

The first thing I did when I got mine 20 years ago was to change out everything that was rubber. Belts and hoses. I flushed the entire system until I had clear water coming out and then I replaced it with a product made for diesel cooling systems. Diesels have some unique characteristics and regular coolants can cause problems. Next you should drain and refill all fluids. This is engine oil, trans fluid, differentials, drop axles, and power steering. These trucks use ATF in the steering system so be aware of that. If you download the Lube Order for the HMMWV it will walk you thru all of this.

 

[Ajax MD]

The first thing I did when I got mine 20 years ago was to change out everything that was rubber. Belts and hoses. I flushed the entire system until I had clear water coming out and then I replaced it with a product made for diesel cooling systems. Diesels have some unique characteristics and regular coolants can cause problems. Next you should drain and refill all fluids. This is engine oil, trans fluid, differentials, drop axles, and power steering. These trucks use ATF in the steering system so be aware of that. If you download the Lube Order for the HMMWV it will walk you thru all of this.

Right. In my post #6 above, I did say that I would replace all fluids. I did catch in the -10 that power steering was ATF fluid. That was important because the power steering needed a little top off for the trip home.

I own an old 5-ton, so I'm aware of the diesel coolant additive but I'll be sure to read the Lube Order and not just make assumptions.

For a cooling system flush, is there a preferred product that HMMWV owners like to use? In the 5-ton forum, everyone just says to use Cascade dish soap. I want something that's really going to de-gunk the system and importantly, the thermostat and heater core.

 

[911joeblow]

These trucks have a nasty tendency to develop steam pockets and stagnant coolant at the back which burps from time to time causing all sorts of temperature spikes and heater issues. Our cooling balance upgrade kits fix these issues. www.paradoxbydesign.com

 

[Ajax MD]

Here's a little update-

The heater core was not leaking or blasting steam. I found an enormous, abandoned mud-dauber nest in the passenger side duct.
When you turn on the blower, the squirrel cage fan would chew on it, sending a blast of fine dust out of the dash register. Then, the flow of air would levitate the mud dauber nest until/unless you hit a big enough bump in the road, which would cause it to hit the fan again.

I detached the duct and turned on the blower and the bug nest shot out like a projectile. It was worn round like a golf ball due to hitting the blower cage.

 

[Coug]

Here's a little update-

The heater core was not leaking or blasting steam. I found an enormous, abandoned mud-dauber nest in the passenger side duct.
When you turn on the blower, the squirrel cage fan would chew on it, sending a blast of fine dust out of the dash register. Then, the flow of air would levitate the mud dauber nest until/unless you hit a big enough bump in the road, which would cause it to hit the fan again.

I detached the duct and turned on the blower and the bug nest shot out like a projectile. It was worn round like a golf ball due to hitting the blower cage.

Thanks for the update, sometimes it's the simple issues that get overlooked.

While you are at it, if you want heat, make sure the fresh air inlet in the passenger foot well is closed down so you're recirculating more warm air, rather than always sucking in cold air. That is, if you want to actually warm up the cabin area.