Engine Runs Hotter than usual

J

jack christensen1

New member
Mar 30, 2008
264
0
0
I set off on a trip the Canada to join GMC 49'ers on a rally to the Canadian Rockies.

10 miles down the road I noticed that the engine was running around 10 degrees hotter than usual and would spike into the 205 region and it wasn't hot
outside. Normally it would be running around 185 to maybe 195.

I took a recent trip up the coast and it was running as usual, so this is a sudden change.

So, cancel the trip or fix it quickly. The work evolves:

So far I've checked the fluid - full to the top.
Concerned that the thermostat was bad - replaced it with a Robertshaw I purchased from Jim K - little change
Concerned that the temp sensor had failed - replaced it, little change.
Checked the lower radiator hose to see if it had collapsed - it was good.
The water pump is not leaking.

The fact that this came on suddenly has me thinking it isn't something like the radiator clogging.

Anyway, I'm hoping for suggestions as to what to do next. New radiator and water pump come to mind unfortunately.

Oh GMC Gurus, Save me and my trip with your advice!

Thanks,

--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
 
Fan clutch comes to mind. Other things might be blown head gasket, bad
pressure cap on the radiator.
Jim Hupy

> I set off on a trip the Canada to join GMC 49'ers on a rally to the
> Canadian Rockies.
>
> 10 miles down the road I noticed that the engine was running around 10
> degrees hotter than usual and would spike into the 205 region and it wasn't
> hot
> outside. Normally it would be running around 185 to maybe 195.
>
> I took a recent trip up the coast and it was running as usual, so this is
> a sudden change.
>
> So, cancel the trip or fix it quickly. The work evolves:
>
> So far I've checked the fluid - full to the top.
> Concerned that the thermostat was bad - replaced it with a Robertshaw I
> purchased from Jim K - little change
> Concerned that the temp sensor had failed - replaced it, little change.
> Checked the lower radiator hose to see if it had collapsed - it was good.
> The water pump is not leaking.
>
> The fact that this came on suddenly has me thinking it isn't something
> like the radiator clogging.
>
> Anyway, I'm hoping for suggestions as to what to do next. New radiator
> and water pump come to mind unfortunately.
>
> Oh GMC Gurus, Save me and my trip with your advice!
>
> Thanks,
>
> --
> Jack Christensen - K6ROW,
> '76 Glenbrook/Clasco - "The Silver Bullet",
> Sebastopol, CA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> Fan clutch comes to mind. Other things might be blown head gasket, bad
> pressure cap on the radiator.
> Jim Hupy

Could also be something as simple as the weights in the distributor finally froze, so that they don't advance the centrifugal timing. Engine will
heat up without sufficient advance. Pull the cap and check the weights. Maybe....maybe not. JWID
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Jack,
Get it fixed quick if you can. We are missing you. Group is currently in
Calgary baking in the heat. Looking g forward to the cool of the Rockies.

Fay Curtis
Traveling with the other 59ers in a borrowed 73 Canyonland
Stampede Dome Calgary, Alberta

> > Fan clutch comes to mind. Other things might be blown head gasket, bad
> > pressure cap on the radiator.
> > Jim Hupy
>
> Could also be something as simple as the weights in the distributor
> finally froze, so that they don't advance the centrifugal timing. Engine
> will
> heat up without sufficient advance. Pull the cap and check the weights.
> Maybe....maybe not. JWID
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
some really great advice so far. I think they have covered most of the bases, I cant think of any others except that if you cant find out why and must
continue as it is. grab a bottle of redline water wetter from one of the big autoparts chains. it wont fix the issue but Ive seen it drop temps in
several cooling systems.

I actually run it in everything now because of that.
beyond that is evans coolant but it requires draining everything out and it is also expensive.

best of luck with it.
 
While all of the previous suggestions are good and should be checked, I think we are avoiding the probable cause. That is a clogged, restricted
coolant flow through the radiator.

I would pull the thermostat and throw it in a pan of hot water on the kitchen stove. Start heating the water and watch the thermostat to see at what
temperature it really opens. Use a mercury type thermometer if you have one. I have seen many bad "new" thermostats.

If the thermostat checks OK then it is time to consider flushing, cleaning, or replacing the radiator.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I'm with KenB. A blown gasket or sticking 'stat would leave some air in the radiator, would it not? Sticking weights could cayuse this to appear
fairly quickly. I bought a little ins[pection camera off eBay or either Banggood - forget which - which could be used to inspect the radiator per Bob
Dunahugh's suggestion. (Actually, I bought it to see if you could tell any difference with colant in the radiator since it's waterproof haven't had a
chance to try it there yet). It was less than 20 bux, works on a laptop or a smartphone. You might try that and have a look if the timing is working
correctly.
Also, while not a great idea for aluminum engines, 'fast flush' properly used might clear the crud if there is some in the radiator. These old iron
engines will withstand the stuff. For the price of it and a couple hours you might find a solution. Beyond that, have a radiator shop take a look.
I've had two recored with good results.

--johnny
--
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" - ol Andy, paraphrased
 
> While all of the previous suggestions are good and should be checked, I think we are avoiding the probable cause. That is a clogged, restricted
> coolant flow through the radiator.
>
> I would pull the thermostat and throw it in a pan of hot water on the kitchen stove. Start heating the water and watch the thermostat to see at
> what temperature it really opens. Use a mercury type thermometer if you have one. I have seen many bad "new" thermostats.
>
> If the thermostat checks OK then it is time to consider flushing, cleaning, or replacing the radiator.

Good suggestion here. Sometimes we miss the obvious. If the radiator is clogged, those spots in the radiator will run cooler than the rest of the
radiator. Hard to do in the application, so DON'T do this with the engine running, but try feeling the radiator with your hand or use a thermal heat
gun to check temps. A lot of cool spots or one large cool spot indicates no water flow...therefor cooler and clogged.
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
There is a lengthy proceedure to test the fan clutch in GM service manual. A quick go/ no go test is that you must have "fan roar" for a couple mins
at cold startup high idle after sitting overnight. This is until the fluid redistributes to the non working chamber after 1 to 2 mins of rotation. If
sufficient fluid has leaked out this roar will be diminished. Your non engaged speed will be below spec and it may not engage on demand . As a side
note I found the 3 NAPA numbers in the interchange are made in USA. I would choose the muddle number if I were buying one.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Here is a quick "fix in a can" that if it helps gets you going. Take a mechanics mirror and light and get a glimpse of the bimetallic spring on front
of clutch.
GM says slight leaking of fluid here is normal. However the oily spring gets packed with road grundge due to the huge volume of aiir passing by to
where it does not change size well. Spray the coiled spring with WD-40 with extension on can. Wait. Spray again. Then try to give the dirt a good
flush away action with final spray. Avoid belts and pulleys though it will wear off. Easy cheap fix if it works and saves clutch swap to continue
your trip.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Another possibility that I haven't heard mentioned is an electrical problem with the gauge. The reason I mention this is that the problem came on so
suddenly.

To test this theory, shoot the thermostat housing with a thermal heat gun and see what the temperature coming out of the engine actually is. It might
just be normal, but your gauge is trying to fool you.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
There's a 'get home' if the fan clutch is toast. Take a couple of small sheet metal screws and drive them into the space between the water pump shaft
and the clutch housing. This will jam the fan on and you will listen to it all the way... but it will keep turning. Be sure you're intending to
replace the clutch before you do this - cos you ARE going to replace it afterwards.

--johnny
--
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" - ol Andy, paraphrased
 
Thanks for all the suggestions which were very helpful.

The fan clutch is OK, the distributor is OK. I used an infra red thermometer on the manifold near the thermostat (which I checked - both were OK)
which showed the same temp as the electronic gauge. The oil looks clean and there's no bubbling in the water in the radiator. I could do a
compression test, but I don't really think it's a blown headgasket at this point.

So, the more I cogitate over all the info, I'm afraid I have to agree with Ken. The radiator is the problem, so it's a trip killer. I'm not
desperate enough to pour magic elixers into the engine and hope they work. But, all is not lost. The Canadian Rockies will still be there in the
fall and with a lot fewer people. What I'll miss most is delaying my trip to visit my Canadian Cousins, who like me, are getting older.

So I either need to get the existing radiator cleaned or get one an aluminum one. My GMC engine has probably at least 110K miles on it and the oil
pressure is low (doesn't always meet the 10 psi per 1000 RPM). Oil tests have been pretty good (I just had one) except for iron which is consistently
around 80 compared to the "Universal Average" of 37. Maybe all this is nature's way of telling me it's time to get the engine rebuilt, radiator done,
etc.

Thanks again!


--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA
 
Particularly if I was going to redo engine and radiator fairly soon, I'd try the fast flush. Either it works or it doesn't, you hazard a few bucks
and most of a day draining flushing and refiling/ If it works you make the rally, if it doesn't you've lost nothing.

--johnny

--
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" - ol Andy, paraphrased
 
There is an aluminum radiator for the GMC on eBay. Apparently a manufacturer and currently 10% off "normal" list price.

Item number is: 163053560599

D C "Mac" Macdonald​
Amateur Radio K2GKK​
Since 30 November '53​
USAF and FAA, Retired​
Member GMCMI & Classics​
Oklahoma City, OK​
"The Money Pit"​
TZE166V101966​
'76 ex-Palm Beach​
k2gkk + hotmail dot com
________________________________
From: Gmclist on behalf of Jack Christensen
Sent: Saturday, July 14, 2018 13:43
To: gmclist
Subject: Re: [GMCnet] Engine Runs Hotter than usual

Thanks for all the suggestions which were very helpful.

The fan clutch is OK, the distributor is OK. I used an infra red thermometer on the manifold near the thermostat (which I checked - both were OK)
which showed the same temp as the electronic gauge. The oil looks clean and there's no bubbling in the water in the radiator. I could do a
compression test, but I don't really think it's a blown headgasket at this point.

So, the more I cogitate over all the info, I'm afraid I have to agree with Ken. The radiator is the problem, so it's a trip killer. I'm not
desperate enough to pour magic elixers into the engine and hope they work. But, all is not lost. The Canadian Rockies will still be there in the
fall and with a lot fewer people. What I'll miss most is delaying my trip to visit my Canadian Cousins, who like me, are getting older.

So I either need to get the existing radiator cleaned or get one an aluminum one. My GMC engine has probably at least 110K miles on it and the oil
pressure is low (doesn't always meet the 10 psi per 1000 RPM). Oil tests have been pretty good (I just had one) except for iron which is consistently
around 80 compared to the "Universal Average" of 37. Maybe all this is nature's way of telling me it's time to get the engine rebuilt, radiator done,
etc.

Thanks again!

--
Jack Christensen - K6ROW,
'76 Glenbrook/Clasco - "The Silver Bullet",
Sebastopol, CA

_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
https://nam01.safelinks.protection.outlook.com/?url=http%3A%2F%2Flist.gmcnet.org%2Fmailman%2Flistinfo%2Fgmclist_list.gmcnet.org&data=02%7C01%7C%7C52b518a152024422478708d5e9badf0e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636671911164221960&sdata=Y1%2BVT4heqne1D3li9b6kRu9pPMEi%2FwQDUUqSS4AWgXo%3D&reserved=0
 
On mine there are tow gauges for water temp. One is engine t, the other is after the radiator.You can see the drop when the fan kicks on.
My PO was a gauge freak- he was a VN era B52 and retired airline pilot

--
76 Glenbrook
 
Here is my suggestion. It only takes a few hours to get that radiator
out of there. It really takes two (or more) people. So call a fix it
day at your place and post an open invite to any GMCer to come and help. Then take
radiator to a local radiator shop and have them test and clean it.

Then last time my radiator was out Rob Mueller called a fix it day at my
hangar. A bunch of GMCers stopped by and they did the job while I took a
had to do trip to Cincinnati and back. We had GMCers from 4 states and one
province here. They did the job including taking it to the radiator
shop in one afternoon so I could go to a GMCMI rally when I returned
from Cincinnati.

The time before that when I had it out was at a GMCMI
rally in Delaware. Again a bunch of GMCers including Colonel Ken and
Emery helped with the swap and we did it in an afternoon with lot of
on lookers.

We did Dan Gregg's at Bean Station in one afternoon.

Get is out and take it to a radiator shop. Then you will know what
you have to do and what your options are.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> I'm not desperate enough to pour magic elixers into the engine and hope they work.

what, Redline Water wetter and Evans coolant? science man! may seem like magic to those who are not familiar with it but these are both tuning tools
that are very effective but even if you have no such tune the redline will drop the water temp by reducing the surface tension thus making the
radiator more effective and evans completely prevents boil overs.
 
Fred, that's quite true - but it's fixing symptoms instead of fixing the problem. Pull it out, have it inspected and whatever's needed done to it,
put it back, and then use Redline and Evans >after< you've determined there are no further leaks or cooling problems. The system is quite capable
when it's working correctly as supplied.

--johnny
--
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" - ol Andy, paraphrased
 
As he said “The system is quite capable
when it's working correctly as supplied.”

So why put in Redline and Evans after it’s fixed. 99.99% or so of the GMCs work fine with a good regular ethylene glycol coolant (Prestone and others).
I would never consider changing to those products. Using those seem like one is just trying to mask a problem. And, do “water wetters” actually work?Ethylene glycol does the same thing and it’s not another additive than can actually interfere with the antifoam, water pump lubricant, and rubber anti-swell additives that are already formulated into a good quality coolant which has been tested by the manufacture to work properly. Once you introduce an additive from someone else you don’t know if it’s compatible with the antifreeze package.

Emery Stora
77 Kingsley
Frederick, CO

>
> Fred, that's quite true - but it's fixing symptoms instead of fixing the problem. Pull it out, have it inspected and whatever's needed done to it,
> put it back, and then use Redline and Evans >after< you've determined there are no further leaks or cooling problems. The system is quite capable
> when it's working correctly as supplied.
>
> --johnny
> --
> 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" - ol Andy, paraphrased
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
You must log in or register to reply here.
Get your shine on at www.cruzingear.co
GMCMI Spring 2026 Rally

Share this page

Share this page
Top Bottom
Back