Hummer h2 limo occassionally overheats

[pteam]

One of our hummer h2 limos occassionally overheats, only occassionally. Bought it used with like 40k miles from another company. It ran fine all winter no over heating.

Now today it gets to 250 degrees we shut it down. Same thing last summer, maybe once a month it would get close to overheating. Today a/c in the front was kinda warm but cold in the back. Does this have anything to do with it? Also there isn't a coolant leak that is noticable as it parks in the same spot everyday inside. What do you think could be causing this? What can be done to solve this or help while we figure it out? We've had it to the dealer last year and they couldn't duplicate the problem nor figure it out.

[tomp]

H2 radiators are not efficient enough for the H2 from the factory. It is ample when everything is brand new but with the slightest amount of debris in the front grill slots, the efficiency goes to crap.

At a minimum, clean out the AC coil in the front by lightly spraying cold water from the rear of the radiator and then from the front. If that helps even the slightest bit, then you are on the right track. If not, try replacing the thermostat.

Finally, I'd have to question what you tranny temps are at prior to the engine overheating? It is possible the your tranny is heating up first due to it being a limo and then causing the antifreeze to climb with it. This is due to the ATF fluid running through the radiator on passenger side. I would suggest a very large efficient aftermarket tranny cooler to replace the cheap OEM unit. Since it's a limo, I would imagine the tranny is working overtime.

I would finally replace ATF and engine oil due to the excessive temps

[pteam]

Thank you good suggestions. I will add these to the lists.

The thing is we have 5 h2 , 4 are limos, and none of the others have problems. All have the stock radiators and tranny coolers and this is the only one to have a problem. So its something out of the ordinary.

We have replaced the thermostat like 5 times. Last time we put a fail safe in it, so if it does overheat (remember its a limo and it does alot of idling at wedding and when 25 people are getting out) the thermostat will stay OPEN. Its not the thermostat.

Would it be ok to completely take out the thermostat for the summer only and put one back in, in the winter? Would this help?

What we plan to do is complete coolant flush, then install extra aux fan in front of the radiator, and 2 aux fans behind the radiator blowing towards the engine.

We put a new radiator and fan on the h2 last year, cant remember if we did the water pump. Could the water pump cause it? Last year we thought it was a leaky head gasket and we ran some sealant in there, and it didnt overheat since then because it didnt overheat all winter, then bam it did it again today.

Thanks for your help guys! Trying to get as many ideas to check as possible.

[SummitUp]

Originally Posted by pteam

Would it be ok to completely take out the thermostat for the summer only and put one back in, in the winter? Would this help?

The primary function of the thermostat is to allow the engine to warm up quickly from a cold start. But it also performs an important function of controlling the actual flow rate of the coolant through the radiator (by creating a restriction). For optimum cooling the coolant needs to pass through the radiator at an optimum rate to allow it time to release or "give up" it's heat. I've seen situations where removing the thermostat actually makes the situation worse because the coolant moves through the radiator so fast it doesn't have time to exchange or release all the heat it could if it were moving through the radiator at a slower rate.

Originally Posted by pteam

Last year we thought it was a leaky head gasket and we ran some sealant in there.

Adding radiator stop leak in an overheating situation is definitely contra indicated. Besides stop leak being nothing more than a temporary band aid for a leak somewhere in the cooling system, it can tend to clog up the coolant galleries running through the radiator and diminish the cooling efficiency even further. I would definitely flush the system and get a <tranny cooler> making sure to bypass the ATF lines going to and from the radiator so at least the heat from the tranny won't be dumped into the radiator.

edit: I should have asked: What is the temperature reading on the tranny temp gauge when your overheating. Also, (a very remote possibility), you may not be overheating at all, but rather you could have a bad temperature sensor sending bad info to the temp gauge on your dash. I've seen it happen...

[pteam]

Heres what I have planned so far, tell me what you think:

1. 160 degree "fail safe" thermostate for hummer h2
2. full coolant flush, going to wash out the inside hoses with a hose
3. single aux fan I believe its 9 inches or 7 inches for in front of radiator on h2
4. double aux fan for behind the radiator to blow into the engine for engine cooling
5. Water Wetter, used to add into coolant of engine to help run coolant cooler, buy 2 bottles

[pdsq99f4]

Make sure your fan clutch isn't just freewheeling in both directions. This could cause it to not pull enough air at idle. Just because you don't see coolant on the ground doesn't mean it's not leaking. Look around the oil pan to make sure the water pump gaskets aren't leaking down the front of the motor and the coolant just drying to the oil pan.

[HUMMERcustoms.com/TAZ]

pteam

I have not forgotten your last PM. It has been hairy and not able to get to laptop much. I will get back to you Friday night or even Sat. morning at 2am if it takes that.

Sorry,

TAZ

[pteam]

Yes I want to publicly thank Taz and Tbarrow for helping me extensivly through PM.

I think the biggest factor might have been we didnt have a fan shroud. We we bought it from the previous company with around 40k miles the fan shroud was all cut up because they put aux fans on. When we replaced the stock fan last year we never put it back on. So we put the fan shroud on.

Also we did a full coolant flush with about 30/70 dexcool/water with water wetter.

Also we added aux fan in front of front radiator / tranny cooler, which we have on some of our other hummers. I would suggest this to some of you guys that are worried about tranny temp before spending alot of money changing radiators etc, this is a much more cost effective setup.

The limo did go out on a 2 hour school luncheon today and its 80 degrees outside total amount of time was about 4 hours running, and never budged past 195.

[HUMMERcustoms.com/TAZ]

Sounds like you have it whipped pteam. I was sure right off the shroud would help as the factory fan sets to far away to pull air through rad.

pteam in limo situation the tran fan was a good idea on your part just as it should be done on all limo's in the world. I'm going to have co2 spray on mine that will only spray at WOT when pushing supercharger etc. It will be on Rad and SC aftercooler so all temps are held down on all the synthetic fluids etc.

Let me know if I can be of anymore help.

I may be getting to Pittsburg next 30 to 60 days so I'll check in with you and have lunch or whatever. I want to catch partsguy also but, he is farther east I think 3 hours or so. It will be for business but, plan on making it part holiday. I have never been to PA so will get to see some of it Ohio and WV while there.

I'm hoping to get to do a good number of different tunes using HPTUNERS.com software this summer depending on how soon we have to go back into paint for new scheme. I will be able to upload tunes to there website. If anyone is using their software on laptop you can check the parameters I had on my setup to see if a tune suites your situation. Then just download them to your software free put it in your H2 and try it out even make all the changes you want to it. It will give some a starting place even if it is not just what you need. HPTUNERS is not VIN specific unless they change anytime soon and pteam could buy one set of software and tune all your H2 limos. I plan to do a normally aspirated engine tune just tweaking it to make the engine tranny etc. more efficient and powerful. That way anyone with factory setup can buy software put it on laptop download check numbers then tweak because of say altitude or extra limo weight. If you read forum at HP you can just about learn everything you could have a question for. I have been there since early 2005 just before the company made huge growth in 2006 with a deal to provide the tunes for all Superchips handheld programmers. Well to long as usual just trying to think of more ways to help Forum BUDS.

Good Luck pteam,

TAZ

[pteam]

I actually live just south of Cleveland. We service Cleveland, Columbus, Toledo and Pittsburgh PA for limo service but it takes us 2 hours to get there and 2 hours back.


If you do make it to Cleveland I definately owe ya at least lunch and a beer or a few hours in a hummer limo for free let me know you should come by our shop and checkout everything

[IRA51]

if you get ahold of Christopher Shull he will get you running nice and cool . www.coolmyduramax.com
if they don't delite my reply again .
yes I know you don't have a GM hd duramax ,but I bet he can solve your problem if you contact him ,good luck .

[HUMMERcustoms.com/TAZ]

pteam

I will be all over the 3 state area so I will make time to get to Cleveland to see the operation. I'm always interested in seeing business I know nothing about. Hey, plus I get to meet a forum Bud. Strongest thing I drink is a soda but, lunch sounds very good just as a bonus to see your operation and maybe Limo to lunch and back to headquarters. We can play it by ear may just come in at Pitt. and leave from Cleveland.

Hey really thanks for the invite and I will accept soon as I can get over.
May beg for a ride in your yellow beast in the avatar. I have never been in one much less near one.

Sincerely Thanks very much!!!!

TAZ