HMMWV Overheat Q's and pictures

[vitamink]

Just got my hmmwv and i'm having overheating issues. Today i took her out for the first time and i noticed that the temp gauge was reading kind of high but didn't waver from that position for a while. I later looked back and it was at 240. I immediately parked the thing and looked under the hood. Everything looked fine, no broken belts, no coolant blowing out anywhere, no steam etc. I got back in and checked the gauges periodically for 30 min. until the heat went down. Luckily i was a block a way from home. I restarted it and it slowly climbed up to a millimeter below 240 by the time i got her home. My reservoir shows coolant up to the fill line and again no steam and the fan is turning fine. Any Ideas or common issues i should look into? What sort of coolant should I use? I'm brand new to diesel engines

 

[FASTNOVA]

Hmmm... I think you need to sell that truck to me to get rid of your problems. I foresee nothing but problems in the future if you keep that truck. If that's not an option you can always verify that your gauge is working properly first then go from there. Do you have a infrared thermometer? Is your fan clutch engaging? Thermostat opening and closing properly? It could be cracked cylinder head or bad gasket, but check the basics first.

 

[tim292stro]

Might be a stuck thermostat, or a corroded water pump impeller... Might drain the coolant system to pop out the water pump and make sure it's actually still attached to the pulley (check the thermostat while you're in there and it's drained).

I put a super sized radiator in my pickup truck and especially on cold days the temperature will climb a bit over the "hot" line until the thermostat pops open, then it drops rapidly back to normal temp.

One thing also, since I'm not familiar with the HMMWV gauges - if it is electrical, most of them will show "hotter" when there is less resistance. If there is a short to ground in the wire anywhere, the gauge will climb - if an open or a broken wire, the temp will drop. For a sanity check you can pull a wire from the temperature sender to the temperature gauge and temporarily wire it in place of the old wire (disconnect the original wire at both ends to remove its effect on the gauge). If you run it with coolant and the temp still climbs like it did before, then it's most likely not the wire. It could still be a bad ground at the gauge though since a bad ground at the gauge would make the gauge think there is more ground at the temperature sender than the gauge, and would make it think the temp is hotter.

Bottom line for electrical, clean, clean, clean and tighten your grounds (really good contact) - and make sure your wires are in good shape and protected. The last thing you want a 24volt truck to do is find a ground return path through the cooling water...

-T

 

[vitamink]

Fast~
I can't sell her, she's perfect...except for this.
The fan clutch is engaging i'm assuming since the fan is spinning. I don't know where the thermostat is, but i'm willing to change it if you think that'd help...i'll even buy one that sets the "on" temperature much lower if that's possible. Any ideas on a part number? I do have a laser thermometer...just point it at the block then?

~Tim
The engine is brand new, gauges are new, wiring harness is new, the trans and transfer case are brand new...everything is brand new except the body, doors and frame. I did contact the guy who built it and he said that it was normal and noted that when he drove it it got up to 240 then cooled to 220. He said that it didn't seem that odd to him, so i took it back out. As he said it heated up to 240 and then it cooled down to 220 then heated back up to 240 etc etc. I will try your gauge idea and connect a different ground wire and see if that helps. It doesn't seem like it's overheating with the stereotypical coolant boiling over, but i'm new to diesel and maybe overheating looks different.

Its the NON turbo 6.5 if i forgot to mention that.

 

[FASTNOVA]

I forgot to ask when did the truck overheat? In traffic? Highway speeds? Climbing a hill?

Use your laser thermometer point it at certain parts of the engine block top, bottom and close to the temp sending unit. If you get temps close to what the gauge on the dash indicates that means your gauge is working. I'm not sure if there is a lower temp thermostat for these.

 

[187]

If you look in the TM the normal operating temps are listed. I believe it's between 180-220? Something is not right, whether it be the gauge, thermostat, etc. There is also a controller (for lack of a better term) under the hood that tells the fan clutch when to operate. One of the HMMWV's that my agency has had this unplugged for some reason when we got it. Just my $.02. I'm no expert.

 

[EMD567]

I bet the the sensor/gauge is bad. Get it warm, and drop some water on the top of the radiator- if the water droplets boil, then you know that the top of the radiator is at least 212ºf. Does the engine smell hot? Pull the dip stick, and sniff the oil- over hot oil has a smell all it's own.

 

[emmado22]

What happens when you unhook the time delay switch?????

 

[tim292stro]

"Everything new" makes me think assembly issue, most likely grounds or a bad connection in general. If everything was out and put back in, I just takes one or two loose grounds to make analog gauges go wonky.

That it seems to come and go leads me to presume vibration is causing a ground in the area around the instruments to open a bit. My best guess without seeing it.

-Tim

 

[tim292stro]

One other thing - the temperature sensor is just a temperature sensitive resistor in a case submerged in the coolant. If they fail, they can have an internal short to the case (ground). This can also make the temp gauge bounce up. If you check the grounds and check the signal wire and it is still doing the same thing, before you drop a $60 on a new temp gauge, try a $15 temperature sender.

If you have a digital multimeter, hook it up between the temperature signal wire and a good ground point - you're going to look at the voltage. With the multimeter in the cab, you should see the number change in sync with a change on the gauge. If it is steady but the gauge is changing a lot, that tells you the gauge has an internal problem.

-Tim

 

[vitamink]

I forgot to ask when did the truck overheat? In traffic? Highway speeds? Climbing a hill?

Use your laser thermometer point it at certain parts of the engine block top, bottom and close to the temp sending unit. If you get temps close to what the gauge on the dash indicates that means your gauge is working. I'm not sure if there is a lower temp thermostat for these.

while driving in traffic it slowly climbs up. If i stomp on the gas it climbs up faster, but gets to 240 then cools down to 220 then back up to 240 before it cools down again.

 

[vitamink]

If you look in the TM the normal operating temps are listed. I believe it's between 180-220? Something is not right, whether it be the gauge, thermostat, etc. There is also a controller (for lack of a better term) under the hood that tells the fan clutch when to operate. One of the HMMWV's that my agency has had this unplugged for some reason when we got it. Just my $.02. I'm no expert.

I hear that if your engine overheats while in the field the quick fix is to unplug the "controller" which causes the fan to run non stop so that you can get it to a mechanic.

What happens when you unhook the time delay switch?????

I will try that next. I assume if my engine cools off i'll need to replace either the controller or the thermostat. If it doesn't cool off then i'll assume its the gauge itself. BTW does anyone know where to get thermostats that flow at a lower temp?

"Everything new" makes me think assembly issue, most likely grounds or a bad connection in general. If everything was out and put back in, I just takes one or two loose grounds to make analog gauges go wonky.

That it seems to come and go leads me to presume vibration is causing a ground in the area around the instruments to open a bit. My best guess without seeing it.

-Tim

It seems more fluid though, not like a drastic jump to 240...it takes a bit. It also cools off slowly. To me it seems the temp gauge is working i don't know if it's exponential as in it says its 240, but it's actually 210. I dunno. I will check the grounds though as i'm looking for anything.

One other thing - the temperature sensor is just a temperature sensitive resistor in a case submerged in the coolant. If they fail, they can have an internal short to the case (ground). This can also make the temp gauge bounce up. If you check the grounds and check the signal wire and it is still doing the same thing, before you drop a $60 on a new temp gauge, try a $15 temperature sender.

If you have a digital multimeter, hook it up between the temperature signal wire and a good ground point - you're going to look at the voltage. With the multimeter in the cab, you should see the number change in sync with a change on the gauge. If it is steady but the gauge is changing a lot, that tells you the gauge has an internal problem.

-Tim

I'll try that too and report back tomorrow.

 

[emmado22]

I'd also check to make sure your sender and gauge are matched.

 

[Augi]

Any autoparts store will have a thermostat for you. This engine is a standard GM diesel. If you need to be specific, ask for a 1994-1996 Hummer H1 NA or an early 90's GMC 2500 HD. They should have various opening temps available. Get a gasket too.

The thermostat is real easy to change. If you look at the top tank of the radiator you will see a fat hose running to the engine (it's less than a foot long and makes a 45degree bend or so). The housing on the engine side that the hose connects to contains the thermostat. It's held together with two bolts and sealed with a gasket. Loosen the hose clamp and remove the hose, then remove the two bolts and the thermostat housing will pop right off.

Don't put the new thermostat in backwards! Take a look at the one coming out to verify the orientation.

Clean all the old gasket crap off with a razor blade before putting it all back together.

Another thing to check is the oil cooler fins. Take a look at the radiator stack and make sure the fins aren't all bent over flat, preventing airflow through the radiators. You could also have corrosion inside the radiators that a radiator shop may be able to deal with.

Augi

 

[Retiredwarhorses]

First things fist.....

you would know if the fan clutch is working cuz when it kicks in you will hear and feel the loss of power.
with engine running cold...unplug the TDM wire...it's the plug with 2 wires not the one with 4.
the fan should move in and out....it fails in the engaged mode, the fan spins regardless, its just then when the fan clutch is engaged it is not free wheeling and its moving air. Also, I find them engaged on most customer trucks...even when everything is working, you need to take a dead blow mallet and whack the crap out of the fan clutch housing...the clutch plates get stuck...I do this on brand new NOS units out of the box...I apply 100psi of air and they won't move in and out till I unstuck them.

2nd, change the thermostat....most are marked which way they go...you need to get one that opens at 180 degrees, order it from kascar.

3rd, how's the coolant

4th, you say the motors new? Rebuilt? New? Seen plenty of New motors that are painted junk...cost one of my customers 3k for the bad motor and 6k for a new motor.

5th' your radiator...is it new? The hmmwv radiator is a PITA, I get them rodded but more then half the time they are toast, remember, they are 28yrs old.

6th, 240 IS NOT NORMAL...Nor is 220, all my trucks...and I have quite a few, plus all my customer trucks I work on and drive, run at 200 with the fan clutch coming on at about 215 which will take it back down to 200 quickly.
it is going to run hotter opinion town then on the open road, you will notice the Fan clutch coming on frequently, it will startle you at times....it's that load at higher speeds.

7th, your gauge is bad....use a thermometer in the overflow tank to see the real temp.


Hope this helps....call me if you need any help.

 

[vitamink]

First things fist.....

you would know if the fan clutch is working cuz when it kicks in you will hear and feel the loss of power.


********While driving, i can hear what i assume is the fan clutch engaging once it gets to 240. I know i hear a high pitched squeek then everything gets really loud and there is some power loss. I had hoped to check it, but while it's stationary it doesn't seem to get hot enough to kick on the fan for me to see. Before, i was convinced it was working at it was spinning when the engine was on, but i guess thats just it free wheeling.

with engine running cold...unplug the TDM wire...it's the plug with 2 wires not the one with 4.
the fan should move in and out....it fails in the engaged mode, the fan spins regardless, its just then when the fan clutch is engaged it is not free wheeling and its moving air. Also, I find them engaged on most customer trucks...even when everything is working, you need to take a dead blow mallet and whack the crap out of the fan clutch housing...the clutch plates get stuck...I do this on brand new NOS units out of the box...I apply 100psi of air and they won't move in and out till I unstuck them.

*******Ok so then fan will move towards and away from the engine when i unplug the tdm wire? I will check tomorrow morning and see. Thank you.

2nd, change the thermostat....most are marked which way they go...you need to get one that opens at 180 degrees, order it from kascar.


********this is the one thing that i had planned on doing anyways so i was way ahead of you. I figured that even if it wasn't the issue, eventually the thermostat would go bad and i'd have a back up. I called Kascar as i wanted to make sure i had the right part. The guy i talked to told me i didn't need one as HMMWV's run really hot and as long as i wasn't having cylinders shutting down or coolant blowing out everywhere then i should be ok. He cautioned that i should check my radiator by holding a flashlight behind it and seeing if it's clogged. I explained that the radiator was "NOS" and that the temp gauge reads 240 before it cools down to 220. He still said that was normal. My reply was, "if normal is on the far end of the gauge, then how do you know when things are abnormal?" He reassured me i didn't need to buy anything, so i didn't. Do you have a part number for the 6.5 from Kascar? I'll order it tomorrow and send you one as well for your help. PM me your address.



3rd, how's the coolant

**********Coolant looks fine. It's at the cold fill line and doesn't look discolored.

4th, you say the motors new? Rebuilt? New? Seen plenty of New motors that are painted junk...cost one of my customers 3k for the bad motor and 6k for a new motor.

***********It was a NOS motor that was inside one of those plastic crates.





5th' your radiator...is it new? The hmmwv radiator is a PITA, I get them rodded but more then half the time they are toast, remember, they are 28yrs old.

***********Radiator is NOS as well, i'm sure that doesn't mean that i couldn't have rust on the inside while looking all shiny black on the outside after sitting in a damp .Gov storeroom. The coolant doesn't appear to be rusty colored though.

6th, 240 IS NOT NORMAL...Nor is 220, all my trucks...and I have quite a few, plus all my customer trucks I work on and drive, run at 200 with the fan clutch coming on at about 215 which will take it back down to 200 quickly.
it is going to run hotter opinion town then on the open road, you will notice the Fan clutch coming on frequently, it will startle you at times....it's that load at higher speeds.

*********It certainly is startling and hard to talk during it's cycle. I figured 240 wasn't normal. I keep getting told otherwise by folks and i can't wrap my head around a gauge that is set up to tell you that everything is good-normal, but not tell you when something has gone awry. That being said, i even find it odd that they don't read normal as dead center for people with "normal" operating temperatures.

7th, your gauge is bad....use a thermometer in the overflow tank to see the real temp.

********That is what i am hoping for most of all, I will employ disconnecting the TDM to check that as well as temp checking the coolant. Work got a little busy for me today and i didn't get the opportunity to do anything. Will the overflow tank provide an accurate reading?


Hope this helps....call me if you need any help.

I really appreciate all the help so far...i wish i lived near California.

I have some questions, are 6.2 and 6.5 parts interchangeable? It was mentioned earlier that the sender and the gauge may not be matched...perhaps he made an error while adding parts..? At what point do you go into "limp" mode?

Here is a history of the Hmmwv as it was explained to me:
It was purchased from a film company and sent to the builder in NJ. It looked in bad shape. The guy building the Hmmwv is an ex-Marine who spent his last years in as a mechanic maintaining Hmmwvs. Once he got out he spends his free time building hmmwvs. Mine was his 9th. Everything was removed an a new 6.5engine/3 speed trans/transfer case were put back in. about 90% of the Hmmwv is NOS. The body and frame are the only thing original to the Hmmwv essentially. Here is a video of it starting...pardon the name its a 20 year old inside joke.

http://www.youtube.com/watch?v=RLcPQsF53j8



Here is a video of it running for the first time that he sent. At 0:18 you'll see the temp gauge. That is the "cool" temperature...then it moves on up to 240, then the fan kicks on and sends it back to 0:18.
http://www.youtube.com/watch?v=Hi-8S8vP858

I talked to him and he said what the guy from kascar said. Even if that is normal range, i'd rather have it running cooler than hotter so i'm willing to swap out whatever to make that happen.

 

[Retiredwarhorses]

Who did you speak with at Kascar? I talk to them every day....I will be more then happy to straighten them out on this issue. Your truck is not in Iraq in sweltering heat, he was in New Jersey on a nice day. The 6.5s I have done run at what I like to say "just left of 200". Does your temp gauge have the led in the right corner? If so, that is supposed to use a "Gray bodied" temp sender, available from Owens export in SoCal for 75.00. One of the gentleman on the G503 did a test and found the diff in temp was I think 15degrees....but on the cool side, not he hot side.Put in a new thermostat....it's a 6.5, tell the auto parts store it's for a 95 Hummer H1, same motor from 94-mid96.My slant back runs hot....but never gets past 220...I say Hot cuz every truck I have or had have alway run 195-200 cruising and 200-215 on hot days and in town with the TDM bringing it back down.The pic of the motor shows a nice GEP motor....and by the way, the last truck I finished here was a Ground mobility Vehicle, the customer bought it from the same guy and shipped it direct to me....it ran perfect.

 

[vitamink]

Who did you speak with at Kascar? I talk to them every day....I will be more then happy to straighten them out on this issue.



************I'm not sure whom. He had a multi syllable first name...not like a dave but more like a jeremy... I dunno.



Your truck is not in Iraq in sweltering heat, he was in New Jersey on a nice day. The 6.5s I have done run at what I like to say "just left of 200". Does your temp gauge have the led in the right corner? If so, that is supposed to use a "Gray bodied" temp sender, available from Owens export in SoCal for 75.00. One of the gentleman on the G503 did a test and found the diff in temp was I think 15degrees....but on the cool side, not he hot side.



************ This is what it looks like. It doesn't appear to have an LED anywhere.





Put in a new thermostat....it's a 6.5, tell the auto parts store it's for a 95 Hummer H1, same motor from 94-mid96.


**********I went to Kascar and they only list 1 for the hmmwv and it's a 6.2 and no operating temp listed. https://www.real4wd.com/zedSuite/catalog/partlist.aspx?CategoryID=150 I will head to an autoparts store now and see what they have available. I need to get some thermal wrapping for some wires anyways. Can i pick you up one while i'm there? I'll mail it to you for all your help. Is this what i'm looking for?
http://www.amazingsavingsautoparts.com/index.php?action=item&id=11000046&adv=froogle


My slant back runs hot....but never gets past 220...I say Hot cuz every truck I have or had have alway run 195-200 cruising and 200-215 on hot days and in town with the TDM bringing it back down.


**********I did the TDM test and the fan spins up and everything gets noisy the second you disconnect the wires. So i'm guessing that's working well.



The pic of the motor shows a nice GEP motor....


***********Yay me! That's good right?

and by the way, the last truck I finished here was a Ground mobility Vehicle, the customer bought it from the same guy and shipped it direct to me....it ran perfect.

***********From the same guy i bought mine from?

***********I was going to do the overflow heat test to see if my gauge is reading correct, but my thermometer is broken. Off to lowes to pick one up. I'll report back.

 

[Retiredwarhorses]

that Thermostat looks correct...My H1 Hummer has 2, they are/were notorious for being bad, mine were stuck open....so the engince never went above 170, regadless of the temp and took some time to get to Operating temp...changed them out and Bammm! All good.

And Yes, Same Guy....Its a 10min Fix....Oh, Get a New Gasket too.....

 

[vitamink]

I just ordered the parts, bought another laser thermometer and ran some checks.

With the dash gauge reading 235ish I popped the hood and pointed the thermometer at the large hose that runs into the top of the radiator. It registered at 189. I then pointed it at the overflow tank and it registered at 178. Now i'm thinking there is something off with the gauge or the temperature sensor.

I went to NAPA to get parts and they gave me a small square gasket and told me that apparently i'd have to shape it and cut holes in it myself ... thought that was kinda odd.


That's cool that you know Chris. He seems like a really nice guy. As soon as i'm done with the coolant system issues, i'll try to figure out what is now leaking down the passenger side frame rail...just noticed that. Awesome.