HMMWV Overheat Q's and pictures

Steel Soldiers is supported by:

171
0
16
Location
Chaska, MN
Diesel are different than gas. They like the increased heat to some degree. You're not far from me, take you gal out today for a 40 mile drive. You should feel and hear the fan kick in. Or if you just want to see what it's like to have the fan run, unplug the time delay module to make the fan engage.
 

shawnshumvee

Member
337
1
18
Location
Janesville WI
Diesel are different than gas. They like the increased heat to some degree. You're not far from me, take you gal out today for a 40 mile drive. You should feel and hear the fan kick in. Or if you just want to see what it's like to have the fan run, unplug the time delay module to make the fan engage.
Thanks for the tip regarding the fan. I always questioned it's operation because it seems to me that it runs like a fixed fan? Running fast/normal speed. but i will unplug the module and see if i get a difference.
 

teteacher101

New member
120
1
0
Location
WI
Really? Wow! Most ICE (internal combustion engines) Gasoline that is, run cooler right around 195. But the Humvee's run a big block (6.2-6.5) so yes a little hotter but 220? So apparently this is normal?
I have a 6.5 with about 18K (Thats what the odometers says anyways) and i haven't hit 200 yet, So i'm good, Really Good?
"Big block, small block", really won't matter as much as a gas engines thermal efficiency being different than a diesel engine. Biggest factor is how the cooling system is designed for X engine and vehicle, but you always have minor discrepancies between like makes an models-especially on older vehicles like we are comparing let alone the temp gauges not being extremely precise either. :) My fan engages around 220 an kicks off around 200, which is about normal per the TM. I haven't put my laser thermometer on anything to check it so it could be slight variances in our gauges too-I would say your good though. :)
 

shawnshumvee

Member
337
1
18
Location
Janesville WI
When my fan was running all the time (bad temp sensor) I don't think it ever got above 180 when driving around in the mid 80s.
Oh yeah? ok i will check that and I'm going to check all that stuff and thinking about a complete cleaning of the cooling system. But what your opinion on running with out a thermostat? I'm not worried about heat she's not a winter machine, i was thinking without a thermostat i will gain maximum flow?
 

TOBASH

Father, Surgeon, Cantankerous Grouch
Steel Soldiers Supporter
1,356
199
63
Location
Brooklyn, NY
Oh yeah? ok i will check that and I'm going to check all that stuff and thinking about a complete cleaning of the cooling system. But what your opinion on running with out a thermostat? I'm not worried about heat she's not a winter machine, i was thinking without a thermostat i will gain maximum flow?
Running a Diesel without a thermostat especially in cooler climates is not a great idea. Diesel engines need a little heat to function and the thermostat lets heat build up prior to allowing cooling.
 

teteacher101

New member
120
1
0
Location
WI
Oh yeah? ok i will check that and I'm going to check all that stuff and thinking about a complete cleaning of the cooling system. But what your opinion on running with out a thermostat? I'm not worried about heat she's not a winter machine, i was thinking without a thermostat i will gain maximum flow?
I second the not a good idea to not run a t. stat unless in a dire situation of course. It probably wouldn't get over 150 degrees on most days-its remarkable how cool engines can run with out one. I highly recommend a coolant flush, when I did mine I had chunks of gunk and rust colored water for several minutes. Its also a good time to replace all of the coolant/radiator hoses while your doing it too. I drained my coolant, an filled with water, added a "flush additive" an ran it till it got warmed up, drained it, refilled again with water, ran it, drained it again. Then I took a garden hose an crammed it into every hose, an outlet an flushed an flushed an flushed until the water looked the same coming out as it did going in.
 

desmodromic

Member
238
18
18
Location
New York, New York
Calling all HMMWV gurus! I need help!

So, my 1990 with a 6.2L has run with no problems for the 2 years that I have owned it. Out of nowhere, the truck stopped cooling properly and will eventually climb to 240 on the gauge if I do not shut her down or pull the TDM wire. It takes 10-15 minutes of hard driving before the truck spikes over 220. Once I disconnect the wire to the Time Delay Module, the truck starts cooling down immediately and will drop below 200 degrees with the fan continuously operating. So the long and short of it is that the fan is not kicking once the engine exceeds ~215 degrees. I have confirm the temp gauges accuracy by surveying various parts of the cooling system with a laser thermometer. I have researched this issue as best as I can and employed all the great advice on this message board to no avail.

I have performed the following maintenance (in order):

1. Replaced the coolant expansion tank cap. Result: no change
2. Replaced the thermostat and topped off the coolant (coolant looks okay and was serviced by the Military in Oct 2015). Result: no change
3. Swapped in 2 different TDMs from two of my other Humvees that operate as they should. Result: no change
4. Swapped in a NOS cadillac valve (then tried all three TDMs). Result: no change.

So I am at a loss. I do not believe it is a water pump/liquid cooling system issue as the truck runs plenty cool with the fan constantly on. What else could be responsible for the fan not kicking on? (I have confirmed that the fan extends and engages when I disconnect the TDM). The only item I have not tested is the temp sensor on the water crossover.

Thoughts?
 

Retiredwarhorses

Well-known member
Steel Soldiers Supporter
2,689
245
63
Location
Brentwood, Calif
Calling all HMMWV gurus! I need help!

So, my 1990 with a 6.2L has run with no problems for the 2 years that I have owned it. Out of nowhere, the truck stopped cooling properly and will eventually climb to 240 on the gauge if I do not shut her down or pull the TDM wire. It takes 10-15 minutes of hard driving before the truck spikes over 220. Once I disconnect the wire to the Time Delay Module, the truck starts cooling down immediately and will drop below 200 degrees with the fan continuously operating. So the long and short of it is that the fan is not kicking once the engine exceeds ~215 degrees. I have confirm the temp gauges accuracy by surveying various parts of the cooling system with a laser thermometer. I have researched this issue as best as I can and employed all the great advice on this message board to no avail.

I have performed the following maintenance (in order):

1. Replaced the coolant expansion tank cap. Result: no change
2. Replaced the thermostat and topped off the coolant (coolant looks okay and was serviced by the Military in Oct 2015). Result: no change
3. Swapped in 2 different TDMs from two of my other Humvees that operate as they should. Result: no change
4. Swapped in a NOS cadillac valve (then tried all three TDMs). Result: no change.

So I am at a loss. I do not believe it is a water pump/liquid cooling system issue as the truck runs plenty cool with the fan constantly on. What else could be responsible for the fan not kicking on? (I have confirmed that the fan extends and engages when I disconnect the TDM). The only item I have not tested is the temp sensor on the water crossover.

Thoughts?
thermostwic switch in the left water cross over....that's where the temp reading is taken from and allows or denies
24v to the TDM....common fail point.
 

911joeblow

Member
Supporting Vendor
473
8
18
Location
Utah
Calling all HMMWV gurus! I need help!

So, my 1990 with a 6.2L has run with no problems for the 2 years that I have owned it. Out of nowhere, the truck stopped cooling properly and will eventually climb to 240 on the gauge if I do not shut her down or pull the TDM wire. It takes 10-15 minutes of hard driving before the truck spikes over 220. Once I disconnect the wire to the Time Delay Module, the truck starts cooling down immediately and will drop below 200 degrees with the fan continuously operating. So the long and short of it is that the fan is not kicking once the engine exceeds ~215 degrees. I have confirm the temp gauges accuracy by surveying various parts of the cooling system with a laser thermometer. I have researched this issue as best as I can and employed all the great advice on this message board to no avail.

I have performed the following maintenance (in order):

1. Replaced the coolant expansion tank cap. Result: no change
2. Replaced the thermostat and topped off the coolant (coolant looks okay and was serviced by the Military in Oct 2015). Result: no change
3. Swapped in 2 different TDMs from two of my other Humvees that operate as they should. Result: no change
4. Swapped in a NOS cadillac valve (then tried all three TDMs). Result: no change.

So I am at a loss. I do not believe it is a water pump/liquid cooling system issue as the truck runs plenty cool with the fan constantly on. What else could be responsible for the fan not kicking on? (I have confirmed that the fan extends and engages when I disconnect the TDM). The only item I have not tested is the temp sensor on the water crossover.

Thoughts?
It is certainly sounding like an electrical issue at this point. I would check for continuity from the sensor back to the controller. Might have a broken lead. Sensors can go bad but not very common.
 

desmodromic

Member
238
18
18
Location
New York, New York
thermostwic switch in the left water cross over....that's where the temp reading is taken from and allows or denies
24v to the TDM....common fail point.
Someone buy this man a steak sandwich. I swapped over the thermostatic switch from a "good" truck and I think everything is copacetic now. It is cooler now and I could not get the truck above 210, but I am fairly certain I heard the fan kick on. I'll have to give her the once over again tomorrow, after a put back together the three other trucks I cannibalized for parts. :(


It is certainly sounding like an electrical issue at this point. I would check for continuity from the sensor back to the controller. Might have a broken lead. Sensors can go bad but not very common.
I am a simple monkey, so swapping a part is easier than the whole proper diagnosis thing. :( If the situation turns south again tomorrow I will properly test the sensor as you suggested.


Thank you for the quick responses, gents!

Cheers
 

parklandtrans

New member
101
0
0
Location
Roy, wa
When the engine is off...open the hood and grab the fan blade and tell me if it spins free or is it locked solid and unable to turn with just hand pressure..?? Normal operation with fan clutch is that fan should NOT BE ABLE TO BE TURNED BY HAND..!!
Please let me know and we'll go from there..I bet a lot of the other guys know where I'm going with this one..
Bob
 

parklandtrans

New member
101
0
0
Location
Roy, wa
Oh yea...forgot to mention in last post...I'd be proud as **** to be stuck on the side of the road in that Lovely Green Girl.
So anytime you want me to road test for you..I'm there My Steel Soldier Brother..!!!
Bob
 

suzukovich

Active member
Steel Soldiers Supporter
357
73
28
Location
Gibsonton Fl
I have been reading this as I am having the same issues. Pretty much have done the same things. I am in Florida so it's been hot here. Don't know if that's an issue but when I was at Hood/NYC or Afghanistan I didn't have this issue.

Sent from my SM-J727U using Tapatalk
 

gtodan

Member
104
17
18
Location
Marion, Iowa
I noticed when the OAT is 65 degrees or more my 1990 M998 runs warmer than usual, usually with the fan kicking in at the appropriate temps. I did some searching on my unit to determine how the airflow thru the system cools the radiator and if there were anything out of place. I discovered there is an aluminum insert in the hood where the hood screen is supposed to be. My unit is from the Wisconsin Natl. Guard"s 132nd CBIT. Would there be a winter part for the hood to use during cold weather ops to allow for more efficient warm-up? I see nothing but the screen NSN in the 24P.IMG_20171125_121101658.jpg

I see what it is, an aluminum armored screen. Putting it back to stock should increase airflow? The vent holes are very small, much more so than the stock unit. Any one have the stock unit?
 
Last edited:

NormB

Active member
Steel Soldiers Supporter
1,205
19
38
Location
Cloverly,MD

suzukovich

Active member
Steel Soldiers Supporter
357
73
28
Location
Gibsonton Fl
From the article: "So you hook it to one battery, then wire it to the transmission control light, giving you the 12-volt ignition source you need."

Hoo-boy. Where have we heard THIS before.

Hook anything 12V up to one battery and watch the battery/charging circuit failures begin popping up.

NB
Get a 24 to 12v inverter

Sent from my SM-J727U using Tapatalk
 
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website like our supporting vendors. Their ads help keep Steel Soldiers going. Please consider disabling your ad blockers for the site. Thanks!

I've Disabled AdBlock
No Thanks