6.2 running at 240 consistently.

[ncreptile]

Had 6.2 M998 over a year. It's always read 230-240f and then fan kicked on. I changed the oil last week and it went up to 238f, never touched 240 and the fan never kicked on. I did notice at random it dropped to 210-220f.

Yesterday I fixed a coolant leak from heater core by bypassing it using 5/8 tube to loop the two engine ports that were connected to the heater core. I used 50/50 green antifreeze from autozone to top it off(VERY LOW in reservoir) as I could not find an extra brand/type to use online.

Today I notice it's getting hot FAST, after 10 minutes of driving it's at 240 but I'm still not hearing the fan. So I'm thinking I've done something wrong, the fan is broken or the temp gauge is wonky. The coolant level has dropped back down to its previous level but I'm not seeing a leak from the hoses I bypassed with?

Any advice is extremely welcome as I'd love to get my m998 back on the road but am worried I'll blow the engine driving it.

 

[drivebymashing]

You could rent a coolant pressure tester at O'Reilly's or Advance Auto Parts. Then you would know for sure there is no small leak.

 

[therooster2001]

I saw the same thing yesterday in mine, I was just cruising around town and it was creeping up. When you're in local traffic, or slowing through neighborhoods, the fan will not kick on when you are decelerating / stopped, the the TDM delays things. On the highway the fan comes on a lot, even at 45-50.

1. You should check the TDM of course, which is super easy. With engine running, disconnect and the fan should kick on, regardless of temp. (the TDM, NOT the EESS). In normal operation, it's supposed to kick the fan on at 230 degrees.

2. Verify temps with a gun at the thermostat and at various points. I am chasing a temp gremlin, and others have also mentioned that gauges are non-trustworthy and they also see "high" temps. I flushed coolant, changes thermostats, changed sending unit and removed a blockage from the coolant overflow return (a common problem I hear). The only thing I didn't do was change the gauge. Its hard to jump out of the truck and get it when it's 240, but be ready to take the temps. I found that my temps were 10 degrees lower than the gauge. I am thinking about running a separate digital gauge so I don't have to jump in and out of the truck until I get to the bottom of it.

3. Grab the fan with the engine OFF (of course) to see if you can move the fan by hand. In normal operation, you shouldn't be able to.

4. Check the coolant mix with a tester, it's probably not the cause though unless you put in 100% coolant and no water. I like to know my levels.


In the end, I have a feeling you're fine, but check all the variables, and be scientific about it. These things run hot. Agree with the above on the coolant pressure testing as well.

Post back your results..

 

[jkcondrey]

With the engine off, can you turn the fan? If you can, you have problems.

 

[jkcondrey]

http://gear-report.com/wp-content/uploads/2017/03/HMMWV A1 Troubleshooting.pdf

try this manual, first section on cooling.

 

[ncreptile]

Thanks for all the help/advice so far. **UPDATE 6/8/18

87f and sunny. Topped off coolant and took her for a spin for an hour stopping/turning off/neutral several times checking with a temp gun. I could not get it hotter than 243f. Also no leaks of any kind, oil and coolant levels good, oil pressure good. I did not hear the fan cut on with the typical brrrrrt noise it makes but I cannot turn it by hand(which is good).

This truck has about 2k miles put on it by me and it's always run hot around 235-240f. Should I leave it be as is or should I be worried and start process of elimination?

 

[ken]

Un plug the fan's temp switch on the coolant crossover. (Drivers side) This will make the fan run all the time. You can unplug this switch with the engine idling when you first start it while the engine is cold. The fan should kick on. If it doesen't then find out why. Something is wrong. If so, go for a drive. See if it still gets to 240. If so, then you need to start looking for the reason why. It should stay around 195 with the fan running all the time. If not, then there is a problem. And you run a better than average chance of blowing a head gasket, cracking a head, and or the block.

 

[therooster2001]

Well, yesterday I changed out the gauge for one from the 5-ton. It's pretty accurate now, but will move a bit when I tap it. I verified the TDM off and on, and the clutch engaged. So good there. I checked all small hoses, overflow nipple again, and then on a hunch checked the radiator cap drain hose. Totally plugged up. That might have contributed as if it couldn't let the pressure out, it will climb in temp. I ran it around, and fan comes on around 215ish, but is a bit spotty when in stop and start traffic / lights. It never got above 220ish, so I think I am dead on in gauge. I have a 6.5 GEP, so think they run hotter than the 6.2. The HMMWV A1 troubleshooting guide referenced 230! I also checked the thermostat housing, then the radiator entrance and exit. About 10-20 degrees (it varied depending on where I was pointing) exiting so I am pretty sure working how it's supposed to. I also power washed the radiators for good measure, but they didn't look clogged at all, or even dirty. Only thing to do is to get the radiator rodded or replaced to see if I can get the last bit. I am a mile high in Denver, and it's hot here, 87-93 degrees now, so I think that's why i run about 10-15 over others. I can't recommend enough to check the overflow smaller hoses. They are definitely a restriction point. I am really curious about the radiator, but we'll see. I will run it around a bit more, but have turned to focus on other projects like inspecting the hubs..