Info needed (over-heating issues) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bdmcgee · 05-06-2009, 05:13 PM

Hello all,

I have a 1969 GMC w/402 BB. . . and she runs a little hot. We've added a ton of performance parts, but the HP hasn't increased so much where my stock 4 core shouldn't handle it. I've put a new thermostat on, all new hoses, new water pump, and have pulled the radiator (clean as a whistle) I have two questions before I pop a gasket myself!

What is the correct pressure rating for the radiator cap? (I suspect I running one that's too low.)

Also, what is the right size (diameter) of the stock water pump & crank pulley? I think it may have been changed out to a larger one along the line somewhere.

Thanks for any help. . . .

JH

Shyguy · 05-06-2009, 05:39 PM

I think I am running a 16# on my stock 350, that is what is called for at auto parts stores. My temp gauge runs down just below the quarter mark.

Is it running hot or is the gauge indicating hot? The gauge on my 454 in a '92 K-3500 use to show pretty high temperatures until I changed the sending unit.

Danny

PanelDeland · 05-06-2009, 06:39 PM

??? Shroud??? Since you didn't mantion it I was wondering if you were running a fan shroud?They can make a big difference.Also,are you running A/C? There are basically 2 things to remember about cooling.The water has to run through the radiator but slowly enough to have time to cool.And the air has to flow thru any obstruction in front of the radiator and through the rad while still cool enough to take heat away.
The other thing that can impact cooling is the amount of heat produced.This could be timing related since the harmonic balancer may have slipped and you couild have timing way different than what shows on your timing light.
Just some thoughts to help guide you thru the process.

myraley · 05-20-2009, 10:56 AM

I am running a 13 lb cap, instead of 16 (but either will work)

cdowns · 05-20-2009, 11:09 AM

what exactly leads you to believe that you are running hot?
have you checked the actuat coolant temp with a known good thermometer? or just going on the 40year old gauge?

So.Cal.Super · 05-20-2009, 03:45 PM

cdowns has a good point, I run a newer temp gauge on mine that actually shows degrees, also did you stick with the factory 195 stat? and last I would ask what kind of condition is your fan clutch in. A simple test, although I'm sure not a 100% accurate is when the engine is up to temp and as soon as it is SHUT OFF grab it. (with keys out of the ignition and after the engine has stopped running) and see if it free spins.
just my .02

**special-K** · 05-20-2009, 09:47 PM

I`m assuming it smells and acts hot.You don`t need a guage for that.Ok,the radiator is clean as a whistle...what exactly do you mean or how did you check it?Did you have it rodded?The shroud is a good question and also what is the fan/clutch situation?Are you runnuing a clutch or direct?

myraley · 05-25-2009, 10:16 AM

Also, some people put a high performance water pump on, but still leave in the old thermostat. If you have a high performance pump, make sure to us the high flow, balanced, deisgn instead of the traditional one, or it can create resistance against the increased water pump flow.

mr48chev · 05-25-2009, 10:23 AM

I'd make sure that the timing is right. Sometimes the rig will start easy and run ok but the timing is late and causes it to run hot.

I had that happen with the 350 Olds in my 51 Merc and am pretty sure it just happened with the 350 in my 71 GMC.

I'm not big on the electric gages and usually run a mechanical gage on all of my rigs.

And add me to those who ask "what makes you think it is running hot"? Are you loosing coolant, gage showing over on hot or ?

myraley · 05-25-2009, 12:10 PM

Thats a good point. But how late would it have to be to make it run hot? Like if the timing should be 46 when cruising on the freeway (which is I believe about the normal advance), what would it need to be to run hot? 35? 25? 15?

mr48chev · 05-25-2009, 12:16 PM

I didn't total time either but 46 sounds like a stretch unless you have a pretty radical engine.

Just out of curiosity, what is it showing on the gage in the truck? Where is the temp needle pointing or is it giving other indications that it is running hot?

To me on a modern engine with a good cooling system and a good cap hot is when it pukes coolant on the ground.

It hasn't by chance been changed to a serpentine belt system has it?

05-06-2009, 05:13 PM	#1
bdmcgee Registered User Join Date: Aug 2007 Location: Central Michigan Posts: 42	Info needed (over-heating issues) Hello all, I have a 1969 GMC w/402 BB. . . and she runs a little hot. We've added a ton of performance parts, but the HP hasn't increased so much where my stock 4 core shouldn't handle it. I've put a new thermostat on, all new hoses, new water pump, and have pulled the radiator (clean as a whistle) I have two questions before I pop a gasket myself! What is the correct pressure rating for the radiator cap? (I suspect I running one that's too low.) Also, what is the right size (diameter) of the stock water pump & crank pulley? I think it may have been changed out to a larger one along the line somewhere. Thanks for any help. . . . JH

05-06-2009, 05:39 PM	#2
Shyguy Junior Member Join Date: Dec 2006 Location: Southeast Missouri Posts: 2,436	Re: Info needed (over-heating issues) I think I am running a 16# on my stock 350, that is what is called for at auto parts stores. My temp gauge runs down just below the quarter mark. Is it running hot or is the gauge indicating hot? The gauge on my 454 in a '92 K-3500 use to show pretty high temperatures until I changed the sending unit. Danny __________________ '67 Chevy C-20 short stepper - build complete, 454/SM-465. '75 C-30 Single Cab DRW-350 small block/NP-435. '77 GMC-6500 Dump Truck, 427 Tall Deck. '92 GMC K-3500 Duallie, 454/4L80E.

05-06-2009, 06:39 PM	#3
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: Info needed (over-heating issues) ??? Shroud??? Since you didn't mantion it I was wondering if you were running a fan shroud?They can make a big difference.Also,are you running A/C? There are basically 2 things to remember about cooling.The water has to run through the radiator but slowly enough to have time to cool.And the air has to flow thru any obstruction in front of the radiator and through the rad while still cool enough to take heat away. The other thing that can impact cooling is the amount of heat produced.This could be timing related since the harmonic balancer may have slipped and you couild have timing way different than what shows on your timing light. Just some thoughts to help guide you thru the process. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

05-20-2009, 10:56 AM	#4
myraley Registered User Join Date: Jul 2007 Location: california Posts: 78	Re: Info needed (over-heating issues) I am running a 13 lb cap, instead of 16 (but either will work)

05-20-2009, 11:09 AM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Info needed (over-heating issues) what exactly leads you to believe that you are running hot? have you checked the actuat coolant temp with a known good thermometer? or just going on the 40year old gauge? __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

05-20-2009, 03:45 PM	#6
So.Cal.Super It'll Buff Out! Join Date: Apr 2007 Location: San Diego Posts: 603	Re: Info needed (over-heating issues) cdowns has a good point, I run a newer temp gauge on mine that actually shows degrees, also did you stick with the factory 195 stat? and last I would ask what kind of condition is your fan clutch in. A simple test, although I'm sure not a 100% accurate is when the engine is up to temp and as soon as it is SHUT OFF grab it. (with keys out of the ignition and after the engine has stopped running) and see if it free spins. just my .02 __________________ "Instructions are just another mans opinion" Become a Supporting Member http://67-72chevytrucks.com/vboard/payments.php Man Card Rules http://67-72chevytrucks.com/vboard/s...d.php?t=634550 72 Chevy Cheyenne Super 400 LWB

05-20-2009, 09:47 PM	#7
special-K Special Order Join Date: Nov 2004 Location: Mt Airy, MD Posts: 85,861	Re: Info needed (over-heating issues) I`m assuming it smells and acts hot.You don`t need a guage for that.Ok,the radiator is clean as a whistle...what exactly do you mean or how did you check it?Did you have it rodded?The shroud is a good question and also what is the fan/clutch situation?Are you runnuing a clutch or direct? __________________ "BUILDING A BETTER WAY TO SERVE THE USA"......67/72......"The New Breed" GMC '67 C1500 Wideside Super Custom SWB: 327/M22/3.42 posi.........."The '67" (project) GMC '72 K2500 Wideside Sierra Custom Camper: 350/TH350/4.10 Power-Lok..."The '72" (rolling) Tim "Don't call me a redneck. I'm a rough cut country gentleman" R.I.P. ~ East Side Low Life ~ El Jay ~ 72BLUZ ~ Fasteddie69 ~ Ron586 ~ 67ChevyRedneck ~ Grumpy Old Man ~

05-25-2009, 10:16 AM	#8
myraley Registered User Join Date: Jul 2007 Location: california Posts: 78	Re: Info needed (over-heating issues) Also, some people put a high performance water pump on, but still leave in the old thermostat. If you have a high performance pump, make sure to us the high flow, balanced, deisgn instead of the traditional one, or it can create resistance against the increased water pump flow.

05-25-2009, 10:23 AM	#9
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,433	Re: Info needed (over-heating issues) I'd make sure that the timing is right. Sometimes the rig will start easy and run ok but the timing is late and causes it to run hot. I had that happen with the 350 Olds in my 51 Merc and am pretty sure it just happened with the 350 in my 71 GMC. I'm not big on the electric gages and usually run a mechanical gage on all of my rigs. And add me to those who ask "what makes you think it is running hot"? Are you loosing coolant, gage showing over on hot or ?

05-25-2009, 12:10 PM	#10
myraley Registered User Join Date: Jul 2007 Location: california Posts: 78	Re: Info needed (over-heating issues) Thats a good point. But how late would it have to be to make it run hot? Like if the timing should be 46 when cruising on the freeway (which is I believe about the normal advance), what would it need to be to run hot? 35? 25? 15?

05-25-2009, 12:16 PM	#11
mr48chev Registered User Join Date: Jul 2007 Location: Toppenish, WA Posts: 15,433	Re: Info needed (over-heating issues) I didn't total time either but 46 sounds like a stretch unless you have a pretty radical engine. Just out of curiosity, what is it showing on the gage in the truck? Where is the temp needle pointing or is it giving other indications that it is running hot? To me on a modern engine with a good cooling system and a good cap hot is when it pukes coolant on the ground. It hasn't by chance been changed to a serpentine belt system has it?

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