Humvee Fan Fighting with Thermostat? (almost always on but temps are good)

[Milcommoguy]

Do you have this one?

Really......... Real men don't read the manual.

Throw money at it and ask SS for free, CAMO

 

[Kevin Donahue]

Really......... Real men don't read the manual.

Throw money at it and ask SS for free, CAMO

I was gonna say lmao... but in all seriousness its helpful if you have little to no knowledge about an engine. Some of it was still enlightening to me even though I've been working on this stuff for a long time.

 

[Kevin Donahue]

*Update* went ahead and replaced the fan controller as well as the thermostat. Both very easy jobs but its a bummer to get coolant everywhere lol.
Gauge is actually reading a bit hotter now, maybe 215-221 but it never really moves much other than when the Humvee is warming up.

The good news is the fan actually seems to cycle like normal now! It will kick on and off several times while I drive.

I am thinking the fan actually is doing a good job of cooling the engine down because what other reason would it have to kick back off all the time if not? Also will run for long periods of time without the fan kicking on at all which is nice.

Still at a loss as to why my gauge is reading around 220 almost all the time but I think I will replace the sending unit next and see what happens... before I replace the gauge it was maxed out at 240+ degrees 24/7 so its worth a shot.

 

[Milcommoguy]

I am glad many got a "giggle" from the goings on here. LOL

Not meant to incite anyone, BUT to gain insight, to read up with the FREE manuals. Lots of newbee's to the HumV experience and some old fart too...just like Tobash and me. No relation, LOL

They are an easy read and not as likely to get yourself has dirty knowing what's going on bumper to bumper or under the hood. Makes for better questions too!

Didn't have an interweb when I started. Think I learned more reading in the outhouse than at school, CAMO

 

[Kevin Donahue]

I am glad many got a "giggle" from the goings on here. LOL

Not meant to incite anyone, BUT to gain insight, to read up with the FREE manuals. Lots of newbee's to the HumV experience and some old fart too...just like Tobash and me. No relation, LOL

They are an easy read and not as likely to get yourself has dirty knowing what's going on bumper to bumper or under the hood. Makes for better questions too!

Didn't have an interweb when I started. Think I learned more reading in the outhouse than at school, CAMO

To me someone linking a TM is kinda like a group of rocket scientists planning the proper velocity and trajectory for re-entering the earth's atmosphere and then someone chimes in with a link to a 4th grade math book that introduces you to the intricacies of adding negative numbers and multiplication without a calculator.... I appreciate the help but I am not an 18 year old grunt out in the field with no tools.

 

[Milcommoguy]

To me that's why I like the TM's. Written for guys like me and maybe a few 100,000 others that just passed the 5th grade. (and VERY GOOD mechanics I might add) It's always good to have different inputs when brainstorming a problem, even if it is from a 4th grader, fresh perspective.

And to add... if the 4th graders input thru the scientists for a loop...then they didn't know what they thought they knowed. YEA 5th grade speak.

All I am saying to the sensitive ones here " the best tools to work on the HumV is the books and the one between your ears"

Is an open book test between man and machine. It's OK here too in the SS study hall. With the books one can turn it into a fact checking, learning experience.

So who's smarter than a 5th grader, CAMO

 

[Ajax MD]

*Update* went ahead and replaced the fan controller as well as the thermostat. Both very easy jobs but its a bummer to get coolant everywhere lol.
Gauge is actually reading a bit hotter now, maybe 215-221 but it never really moves much other than when the Humvee is warming up.

The good news is the fan actually seems to cycle like normal now! It will kick on and off several times while I drive.

I am thinking the fan actually is doing a good job of cooling the engine down because what other reason would it have to kick back off all the time if not? Also will run for long periods of time without the fan kicking on at all which is nice.

Still at a loss as to why my gauge is reading around 220 almost all the time but I think I will replace the sending unit next and see what happens... before I replace the gauge it was maxed out at 240+ degrees 24/7 so its worth a shot.

I know that seems hot but from everything I've read and my own personal experience, that sounds like textbook temperatures and behavior. I think you've nailed it.

The downside of the design is that there are no dummy lights or warning buzzers if you overheat and the range on the gauge from 220F to "overheated" is a very narrow slice, visually. You simply have to be vigilant while driving. The fan cycling normally is a good audio cue that can help relieve you of the need to constantly babysit the temp gauge.

 

[DREDnot]

I was half thinking about getting one of the newer style gauges that seems more informative
AND come with an idiot light

 

[Ajax MD]

@DREDnot someone pinged me offline and told me about that newer style gauge. When did that come out?
Seems like an easy upgrade if you buy the proper sending unit.

Not only does it include the warning light, the range of movement of the needle between "normal" and "overheating" is much more obvious and more likely to catch your eye.

 

[Kevin Donahue]

Another update- went ahead and put a new sending unit in it. Little to no change, actually reports a tad bit hotter now around 222/223.... Other than warming up the Guage is basically a statue. It stays at that temp the entire trip and does not move a milimeter.

I also installed the Paradox by Design cooling system. I would say she runs the fan 50% less often on back roads and maybe 20% less on the freeway. If nothing else it's better for those rear cylinders though.

Other than the temp gauge always being around 222 or so now it seems to be a good normal running 6.5 with normal fan cycles so I am a but at a loss. Maybe this is just normal and I should give up on expecting that guage to move down to 190 after the fan has cycled?

Another thing, the laser temp gun always reads around 185-195 at the area of the Guage sending unit. Not 220ish.

If my understanding of the sending unit is correct it operates by grounding itself through the block/coolant and a hotter temp will make for a better ground therefore Guage will move to the right? Mine only has one wire so I am assuming that's how it works.

What do you think the next step is? Throw another Guage at it? Rig up a wire from the Guage to the sender and go for a drive? Or just leave it is always a choice too.

Thank you everyone for the help so far!!!

 

[Kevin Donahue]

I know that seems hot but from everything I've read and my own personal experience, that sounds like textbook temperatures and behavior. I think you've nailed it.

The downside of the design is that there are no dummy lights or warning buzzers if you overheat and the range on the gauge from 220F to "overheated" is a very narrow slice, visually. You simply have to be vigilant while driving. The fan cycling normally is a good audio cue that can help relieve you of the need to constantly babysit the temp gauge.

Does your Guage usually move after the fan kicks on or is there little reaction? I get maybe 2 degrees if that but the fan cycles off which tells me it's more like 15-20 degrees over the course of a full cycle.

 

[HoveringHMMWV]

My 1097A2 has a 6.5L NA GEP and operates just as you’re describing. The engine will warm up to 220 and then the fan will begin to cycle on and off according to driving conditions. With the fan engaged, the temp gauge never cools down more than 5 deg. Peak temp has never been higher than 220. Fan cycles are approximately 35+/- seconds on and 1.5-3 minutes off (depending on driving conditions).
- HoveringHMMWV

 

[Ajax MD]

Does your Guage usually move after the fan kicks on or is there little reaction? I get maybe 2 degrees if that but the fan cycles off which tells me it's more like 15-20 degrees over the course of a full cycle.

Yes it moves, but not much. 15F-20F degrees on that gauge is not a lot of travel. It's also a lagging indicator. The needle doesn't usually drop until shortly after the fan shuts off and the engine has a chance to ingest the cooler anti-freeze from the radiator. (I guess)

 

[Retiredwarhorses]

Another update- went ahead and put a new sending unit in it. Little to no change, actually reports a tad bit hotter now around 222/223.... Other than warming up the Guage is basically a statue. It stays at that temp the entire trip and does not move a milimeter.

I also installed the Paradox by Design cooling system. I would say she runs the fan 50% less often on back roads and maybe 20% less on the freeway. If nothing else it's better for those rear cylinders though.

Other than the temp gauge always being around 222 or so now it seems to be a good normal running 6.5 with normal fan cycles so I am a but at a loss. Maybe this is just normal and I should give up on expecting that guage to move down to 190 after the fan has cycled?

Another thing, the laser temp gun always reads around 185-195 at the area of the Guage sending unit. Not 220ish.

If my understanding of the sending unit is correct it operates by grounding itself through the block/coolant and a hotter temp will make for a better ground therefore Guage will move to the right? Mine only has one wire so I am assuming that's how it works.

What do you think the next step is? Throw another Guage at it? Rig up a wire from the Guage to the sender and go for a drive? Or just leave it is always a choice too.

Thank you everyone for the help so far!!!

As I stated in my first comment, your system is operating normal, your temps are normal....your chasing you tail and spending money you don’t need to spend, this seems to be something I see folks Constantly doing Because they have never owned a diesel, mil vehicle or hmmwv Before.
i own about 13 of my own hmmw, all are A2 up too M1165A1 with geared fan drive....they operate at 220 degree.
There is only a single component that controls the temp that engages the fan system, it’s not the TDM, cadillac valve or thermostat, it’s the thermostatic switch, if you control that, you control fan engagement.
Your tstat Tstat starts to open at 185-190, fully open at 205, these are not exact numbers, same is to be said for thermostatic switch. But usually within a couple degrees.

 

[Kevin Donahue]

As I stated in my first comment, your system is operating normal, your temps are normal....your chasing you tail and spending money you don’t need to spend, this seems to be something I see folks Constantly doing Because they have never owned a diesel, mil vehicle or hmmwv Before.
i own about 13 of my own hmmw, all are A2 up too M1165A1 with geared fan drive....they operate at 220 degree.
There is only a single component that controls the temp that engages the fan system, it’s not the TDM, cadillac valve or thermostat, it’s the thermostatic switch, if you control that, you control fan engagement.
Your tstat Tstat starts to open at 185-190, fully open at 205, these are not exact numbers, same is to be said for thermostatic switch. But usually within a couple degrees.

Fair enough, just don't understand why people say theirs runs at 200, fan kicks on at 210, then cools it down to 185 while mine runs at 221-223, fan kicks in, no difference on the gauge ever. Something just doesn't add up to me.

 

[Retiredwarhorses]

Fair enough, just don't understand why people say theirs runs at 200, fan kicks on at 210, then cools it down to 185 while mine runs at 221-223, fan kicks in, no difference on the gauge ever. Something just doesn't add up to me.

A0/A1 trucks....I have a couple A0’s that work that way. Again...fan engagement based on thermostatic switch opening and closing. Funny thing is, there is only one part Number for the switch, some seem to open earlier than others.
thermostatic switch Is notorious for failing, or ranging from 200-220...no idea why.
but ALL A2’s I’ve had are 220 fan engagement....

 

[Kevin Donahue]

A0/A1 trucks....I have a couple A0’s that work that way. Again...fan engagement based on thermostatic switch opening and closing. Funny thing is, there is only one part Number for the switch, some seem to open earlier than others.
thermostatic switch Is notorious for failing, or ranging from 200-220...no idea why.
but ALL A2’s I’ve had are 220 fan engagement....

Interesting, well if that is the case then the fan is coming on pretty much right on the money. And with your A2s do you ever see any cool down on the Guage by the time the fan shuts back off or is it miniscule? I do have a good bit of experience with diesels, even 6.5s in Civilian stuff, but never had one that doesn't have noticeable cool down after the fan runs.

FYI I did change the fan switch earlier on because my fan was running almost always (threshold was way too low on the old switch). This didn't really do anything for indicated temp but made the fan cycle like normal.

Weirdly, with the new Guage on the old thermostat my temps were always around 200 - 210 so I guess it's safe to assume the brand new one I put in runs a bit hotter.

 

[Dpas1973]

I’m going to flush my cooling system is there bleed valve that need to be opened?


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[Milcommoguy]

I’m going to flush my cooling system is there bleed valve that need to be opened?


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You mean this doo dad?



That's a big one, CAMO

 

[Dpas1973]

You mean this doo dad?

View attachment 812898

That's a big one, CAMO

No I read in another post someone was told these is other bleed valves or something didn’t quite understand.


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