Home » Public Forums » GMCnet » Trying to HELP - GMC owner with overheating issue when going up mountains.
| Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360024] |
Mon, 09 November 2020 12:22  |
UV520
Messages: 3
Registered: February 2020
Karma: -2
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Hello everyone,
I'm trying to help someone that has an overheating issue with his GMC. (I believe it's a 455 and I will confirm as I've gotten since last night.)
Every time they use it up mountains going to higher altitudes it overheats badly.
(FYI - I'm a retired ASE and US Army mechanic and I DON'T want him to just throw parts at it.)
My hope is that other GMC owners have experienced this with their coach and that there are some proven upgrades he can do; as I want to make sure that he does the right and best upgrades to his cooling system and NOT simply for him to replace parts until it is finally fixed.
Your help is appreciated.
Sincerely, Tony
[Updated on: Mon, 09 November 2020 12:25] Report message to a moderator |
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360025 is a reply to message #360024] |
Mon, 09 November 2020 14:16  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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1st thing - does not need to be "upgraded" a good stock coach will not overheat.
but, there are a few things he needs to do...
BAsics - check timing with a timing light. make sure the advance mechanism is working on distributor.
know the thermostat is working. 195 degree in my experience is the one to have. Some say 185, I highly disagree.
know that the fan clutch is good. Some say new fan clutch's are random on how well they work, but I installed a Napa part#271303 2747 fan clutch this past summer, and i know about 4 others that have as well and so far all are workers.
after that, it seems our 45 year old radiators can be not working as well as it should. myself, and i know others had engines that tended to get a little warm under load, and a new radiator fixed that problem. mine was pretty gunked up.
dont be trying to drag heavy cars up the mountains either.... a good coach should have no issue with that, but the amount of extra load that creates is crazy big, and if you have other mechanical issues it will only compound trying to isolate the issue.
if they still have problems after making sure the above is all in perfect order, let us know for further possible issues.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360026 is a reply to message #360025] |
Mon, 09 November 2020 14:20 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I should add. an IR temp gun is a very handy tool to help figure out what is going on with cooling system, but it is not perfect. STill a tool one should be getting out and using if you are having temp questions.
you can check the upper and lower hose temps, the thermostat housing. you can compare to what gauge readings are.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360027 is a reply to message #360024] |
Mon, 09 November 2020 15:59 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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UV520 wrote on Mon, 09 November 2020 13:22Hello everyone,
I'm trying to help someone that has an overheating issue with his GMC. (I believe it's a 455 and I will confirm as I've gotten since last night.)
Every time they use it up mountains going to higher altitudes it overheats badly.
(FYI - I'm a retired ASE and US Army mechanic and I DON'T want him to just throw parts at it.)
My hope is that other GMC owners have experienced this with their coach and that there are some proven upgrades he can do; as I want to make sure that he does the right and best upgrades to his cooling system and NOT simply for him to replace parts until it is finally fixed.
Your help is appreciated.
Sincerely, Tony
Tony,
I am glad that your friend has you on his side. Please advise him to join this forum at his first opportunity.
Jon had things very right about the first checks. A coach should not have any difficulties such as that, but they are all forty+ years old. As per Jon, ask him if he hears the fan roar on all cold starts. He should. If there is doubt, if he should try to spin the fan cold. It should not spin easily. That would be my first check. A failed fan clutch is not easy to detect unless you know to look for it. Passcars don't seem to have this problem because they typically don't get run at these loads and are seldom this age. If there is goo in the thermal spring on the front. Clean it with brake cleaner before you replace the clutch. But it there is, plan to replace it in the future.
The coaches cooling system does need the ram air through the front, and if there have been any mods up there, you should look them over carefully. My great joke there is that a contact that tows a 5er, had heat issues and so he put a fan in front of the radiator and it got worse. Well his fan clutch was bad too.
Is the fan shroud intact? Some people like to take it out, well, GM put it there for a reason....
The last thing I will add is that the stock carburetors do not do well over about 9KMSL - they can go lean and that makes for hotter. This is my experience, but if you step into it more, you can "flush" that old quadrajet and dump in enough fuel to cool things at the expense of fuel.
Run Jon's list first.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360029 is a reply to message #360024] |
Mon, 09 November 2020 16:23 |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Tony,
Your line referring to higher altitude makes me question the radiator cap. It needs to maintain 11 psi (or AT LEAST 9 psi as some replacements do) to prevent boiling at altitude. Of course 50% anti-freeze is required.
Other than that, the replies about fan clutches are good. The ONLY time my GMC overheated was on a 100 degree day, with the A/C on, after about 1/2 hour at full throttle climbing into the mountains west of Denver. That's how I discovered my fan clutch, which had always been unusually quiet for 20 years, was bad.
A clogged or limed up radiator is also a good possibility. Rather than just replacing it, take it to a radiator shop and have it "rodded out" if possible. (Remove tanks and physically clean the passages in the core.) If you can afford it, a new aluminum radiator from Jim K is good, IFF you need it.
HTH,
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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| Re: [GMCnet] Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360030 is a reply to message #360029] |
Mon, 09 November 2020 17:29 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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I suspect the Fan clutch.
By the time the engine is getting hot, you cannot help but hear the Fan
cranking up, should that not happen,then replace it.
On Mon, Nov 9, 2020 at 2:23 PM Richard H Staples via Gmclist <
gmclist@list.gmcnet.org> wrote:
> Tony,
> Your line referring to higher altitude makes me question the radiator
> cap. It needs to maintain 11 psi (or AT LEAST 9 psi as some replacements
> do) to
> prevent boiling at altitude. Of course 50% anti-freeze is required.
>
> Other than that, the replies about fan clutches are good. The ONLY time
> my GMC overheated was on a 100 degree day, with the A/C on, after about 1/2
> hour at full throttle climbing into the mountains west of Denver. That's
> how I discovered my fan clutch, which had always been unusually quiet for 20
> years, was bad.
>
> A clogged or limed up radiator is also a good possibility. Rather than
> just replacing it, take it to a radiator shop and have it "rodded out" if
> possible. (Remove tanks and physically clean the passages in the core.)
> If you can afford it, a new aluminum radiator from Jim K is good, IFF you
> need it.
>
> HTH,
>
> Rick Staples
>
> --
> Rick Staples, '75 Eleganza, Johnstown, CO
>
> "Advice is a dangerous gift, even from the Wise to the Wise, and all paths
> may run ill." -Tolkien
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.gmcrvparts.com
1-800-752-7502
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Jim Kanomata
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360037 is a reply to message #360024] |
Tue, 10 November 2020 07:21 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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Keep ion mind, the OEM radiator cap is 9PSI. Follow the suggestions above, checking the fan clutch cold being the easiest. Sending the radiator to a shop for cleanout is the hardest but may be necessary. Timing and distributoe weight movement is in the middle. Also check for vacuum leaks.
Tony, how about a name so we know who you are when we meet ata rally, and a location so if there's a GMCer in striking distance s/he'll be aware.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360052 is a reply to message #360039] |
Tue, 10 November 2020 11:07 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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I live in a mountain state and what worked for me a good radiator is a must.I my case an aluminum one from jimmy k. Second a good fan clutch 2797 that roars when it comes on at around 210 degrees 180 or 195 thermostat. Down shift to 2nd when the grade starts getting steep. Most long grades around here are 6 or 7% . I always tow a Honda CR-V so 3:70 gearing is my choice of final. On 100 degree day the roaring fan going on and off will be music to your ears as you climb a steep mountain grade don’t forget a good stacked plate trans cooler for the tranny.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360056 is a reply to message #360026] |
Tue, 10 November 2020 15:45 |
TR 1
Messages: 348
Registered: August 2015
Location: DFW
Karma: -7
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Senior Member |
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lqqkatjon wrote on Mon, 09 November 2020 14:20I should add. an IR temp gun is a very handy tool to help figure out what is going on with cooling system, but it is not perfect. STill a tool one should be getting out and using if you are having temp questions.
you can check the upper and lower hose temps, the thermostat housing. you can compare to what gauge readings are.
Another good use of the IR gun is you can check various points on the rad to see if there are dead areas due to clogs, corrosion, etc.... Also a good way to confirm coolant is flowing through the radiator effectively. Should be hot on the drivers side top to bottom, and cooler as you move across to the passenger side. Once you confirm the coolant is moving through the rad, then look at things like airflow, fan clutch, etc.... If not enough coolant is moving through the rad, there may not be enough heat being rejected by the rad to even activate the fan clutch....
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360058 is a reply to message #360024] |
Tue, 10 November 2020 16:59 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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I fought overheating problems for a long, long time and after trying everything else I finally determined that it was due to a cracked head on the driver's side in the front-most cylinder. It might be a cheap enough test to have some of your friend's coolant analyzed by a lab for the presence of combustion products so that this particular problem can be either confirmed or ruled out.
Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360078 is a reply to message #360076] |
Thu, 12 November 2020 09:40 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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rgogan wrote on Thu, 12 November 2020 09:55I have had an overheating problem, but when pressurizing my cooling system to check it, there is no drop in pressure over 2 hrs. However, others have said that a combustion leak can be temperature sensitive and only show up when the engine is hot.
I would not interpret a no-leakdown pressure test as proof that there were no combustion leaks based on my personal experience. My overheating problem caused by a cracked head was indeed pressure sensitive as cruising the interstate at 55 MPH was no trouble but speeding up to 65 would produce overheating in short order.
Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360082 is a reply to message #360076] |
Thu, 12 November 2020 11:36 |
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Richard RV
Messages: 631
Registered: July 2012
Location: Full-timer for 12 years, ...
Karma: -17
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Senior Member |
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Not Harbor Freight, but I bought a kit online and tested it on a friend's late 90's Northstar Cadillac which had overheating problems and I had my suspicions. It did pick up combustion gases in the coolant. A known issue with those Cadillacs.
Now I need to figure out how to MacGuyver a way to connect the combustion tester to the fairly well hidden GMC radiator neck...
Richard
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemont waiting its turn
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| Re: Trying to HELP - GMC owner with overheating issue when going up mountains. [message #360102 is a reply to message #360082] |
Thu, 12 November 2020 21:11 |
UV520
Messages: 3
Registered: February 2020
Karma: -2
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Junior Member |
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Richard RV wrote on Thu, 12 November 2020 11:36Not Harbor Freight, but I bought a kit online and tested it on a friend's late 90's Northstar Cadillac which had overheating problems and I had my suspicions. It did pick up combustion gases in the coolant. A known issue with those Cadillacs.
Now I need to figure out how to MacGuyver a way to connect the combustion tester to the fairly well hidden GMC radiator neck...
Richard
Richard,
At times I've used the overflow tank when I could not get to the radiator. Plus it normally is a better place to test anyways. When you release the pressure and the coolant flows into the the tank it is normally not high enough to contaminate the tester, as a radiator sometimes can.
KEYS POINTS: Only does this if you have a radiator cap with a lever and ONLY lift the lever. NEVER try to remove the cap when hot. The overflow tube from the radiator needs to go into the bottom of the overflow tank. The overflow tank needs to be at normal level, so not to contaminate the tester.
[Updated on: Thu, 12 November 2020 21:13] Report message to a moderator |
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