clogged radiator or bad thermostat? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

69 XCamper · 04-11-2003, 07:18 PM

If I start my engine & let it idle, it gets hot to the point of massive pressue coolant release via the overflow tube. The guage reads close to hot when this happens. Is this as simple as a thermostat stuck closed or could it be a clogged radiator.

cdowns · 04-11-2003, 07:47 PM

i dunno but if it was me i'd change the thermostat b-4 i'd get a new radiator

oldsub86 · 04-11-2003, 08:31 PM

How long have you had the truck? Has the rad been changed or recored? You can try the thermostat first but if it is old it may be plugged. I had to have the one in my truck recored because it started to overheat and spit antifreeze regularly.

Pilgrim · 04-11-2003, 09:12 PM

Do the simplest thing first.

trailwart · 04-11-2003, 10:09 PM

just pull the thermostat and let it run, you will then find out if it was a stuck thermostat or a cloged rad.

Blue Beard · 04-11-2003, 11:24 PM

You could even have a plug in a hose or heater core..............

Capitol68 · 04-11-2003, 11:40 PM

how about the fan clutch ?

*dtlilly* · 04-12-2003, 12:05 AM

I'd feel your radiator after it got hot. Place your hand from top to bottom along the cooling fins (with engine off). If the bottom of the radiator is cooler at the bottom than the top, you can assume the radiator is getting stopped up. If there are no leaks, and the radiator is in good shape, send it to a radiator shop to have the tanks pulled off, everything boiled, and rod the cores.

If there is a constant temp from top to bottom, and you replaced the thermostat, you may have a problem with a (or both of), the heads. If the heads are suspect, take your radiator cap off (when cool), start the engine, and see if you see bubbles in the fluid. If so, the combustion of the engine is getting in to the water jacket (usually a bad head gasket from the inside). Not all head gasket breaks will cause white smoke from the exhaust.

spinning wheels · 04-12-2003, 01:17 AM

Check your radiator cap or just replace it with a new 13lbs cap.
Don't overlook a bad water pump....
If the truck is getting so hot, that the over flow starts boiling over. Chances are that the thermostadt is opening, since the hot water is circulating from the hot motor. Check for the bubbles in the radiator, (for bad head gaskets).
Also, make sure your motor is timed correctly and that your lubrication system is up to snuff. Make sure you have oil in the motor

I have seen overheating motors due to lack of motor oil.
Finally, make sure your carb is tuned correctly. Make sure its not too lean.
Good luck, I'm still chasing my overheating gremlins, but I'm making it an experiment. I'm going to change items one at a time, just to see what works or improves the cooling system. Going to change Fan, water pump, radiator, ect...

Bill72BB · 04-12-2003, 01:30 AM

IMOP , The Thermostat needs to be replaced.

O'l Buck · 04-12-2003, 02:24 AM

Mine used to do that.....it was the radiator, but I knew it was the radiator because the fins were all mashed up and the previous owner had about half of the core blocked to keep it from leaking.

A.P. · 04-12-2003, 06:02 AM

My truck would over heat and what I did was replace the thermostat and sent the rad to get clean. It now working fine. Good luck with your problem.
A.P.

69 XCamper · 04-12-2003, 11:05 PM

OK, I pulled out the thermostat and now it runs very cool. The radiator seems to be flowing fine. I'll pick up a new thermostat and drop it in tomorrow.

Blue Beard · 04-13-2003, 09:20 AM

Another satisfied member................

04-11-2003, 07:18 PM	#1
69 XCamper Registered User Join Date: Feb 2003 Location: Lake In The Hills, IL Posts: 28	clogged radiator or bad thermostat? If I start my engine & let it idle, it gets hot to the point of massive pressue coolant release via the overflow tube. The guage reads close to hot when this happens. Is this as simple as a thermostat stuck closed or could it be a clogged radiator. __________________ 69 Chevy C20 (stock & waiting) 69 Datsun Roadster SPL311 (still waiting for resto) 02 Hyundai Elantra GT 00 Ford Expedition 99 Coleman Utah Lake In The Hills, Illinois

04-11-2003, 07:47 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	i dunno but if it was me i'd change the thermostat b-4 i'd get a new radiator __________________ 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

04-11-2003, 08:31 PM	#3
oldsub86 Registered User Join Date: Dec 2002 Location: Canada Posts: 695	How long have you had the truck? Has the rad been changed or recored? You can try the thermostat first but if it is old it may be plugged. I had to have the one in my truck recored because it started to overheat and spit antifreeze regularly. __________________ 1968 Chevy - 292 with a powerglide

04-11-2003, 09:12 PM	#4
Pilgrim Registered User Join Date: Mar 2003 Location: Crescent City, FL Posts: 492	Do the simplest thing first. __________________ Bob 68 C20 Camper Special

04-11-2003, 10:09 PM	#5
trailwart Registered User Join Date: Mar 2003 Location: michigan Posts: 356	just pull the thermostat and let it run, you will then find out if it was a stuck thermostat or a cloged rad. __________________ 72 chevy 3\4 ton 4 speed 4x4 84 1\2 ton 4x4 (gone but not forgotten, thanks for the memories) 1999 suburban 4x4 1982 chevrolet S-10 V-8 (Thanks uncle EARL)

04-11-2003, 11:24 PM	#6
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,834	You could even have a plug in a hose or heater core.............. __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo

04-11-2003, 11:40 PM	#7
Capitol68 Registered User Join Date: Sep 2002 Location: Austin,Tx Posts: 327	how about the fan clutch ? __________________ '68 Fleet LWB orig 307 .030 over GM Hei/w Accel Super coil orig. stock TH 400. _______________________ “What we do for ourselves dies with us. What we do for others and the world remains and is immortal.” Albert Pine English author d.1851

04-12-2003, 12:05 AM	#8
dtlilly Account Suspended Join Date: Jan 2003 Location: Shadow of Lambeau Field Posts: 5,597	I'd feel your radiator after it got hot. Place your hand from top to bottom along the cooling fins (with engine off). If the bottom of the radiator is cooler at the bottom than the top, you can assume the radiator is getting stopped up. If there are no leaks, and the radiator is in good shape, send it to a radiator shop to have the tanks pulled off, everything boiled, and rod the cores. If there is a constant temp from top to bottom, and you replaced the thermostat, you may have a problem with a (or both of), the heads. If the heads are suspect, take your radiator cap off (when cool), start the engine, and see if you see bubbles in the fluid. If so, the combustion of the engine is getting in to the water jacket (usually a bad head gasket from the inside). Not all head gasket breaks will cause white smoke from the exhaust.

04-12-2003, 01:17 AM	#9
spinning wheels Registered User Join Date: Sep 2001 Location: Hacienda Heights, California USA Posts: 474	Check your radiator cap or just replace it with a new 13lbs cap. Don't overlook a bad water pump.... If the truck is getting so hot, that the over flow starts boiling over. Chances are that the thermostadt is opening, since the hot water is circulating from the hot motor. Check for the bubbles in the radiator, (for bad head gaskets). Also, make sure your motor is timed correctly and that your lubrication system is up to snuff. Make sure you have oil in the motor I have seen overheating motors due to lack of motor oil. Finally, make sure your carb is tuned correctly. Make sure its not too lean. Good luck, I'm still chasing my overheating gremlins, but I'm making it an experiment. I'm going to change items one at a time, just to see what works or improves the cooling system. Going to change Fan, water pump, radiator, ect... __________________ '72 GMC custom camper 350/350

04-12-2003, 01:30 AM	#10
Bill72BB Thats the Hillbilly way Join Date: Jul 2001 Location: Torrance,Ca Posts: 5,980	IMOP , The Thermostat needs to be replaced. __________________ BILL Torrance Calif 90504 Member DUF Club Member Old Farts Club 72 3/4ton Custom Camper BB402/400 trans Dynomax Cerama-coat headers , Hei distributor ,Edelbrock 1411 air,ps,pb,leafsprings ,98 chevy 60/40 seat,S10 shoulder belts tilt,3.54 Dana 60 rear. 16" Eagle wheels with LT265/75 16 tires,Gaylord Lid,H4 headlights with 100W relay conversion. " If I knew I was going to live this long I would have taken better care of myself " Marriage changes passion...suddenly you're in bed with a relative. A GUY'S PRAYER.... Lord, I pray for a nympho with huge boobs who owns a liquor store and likes to fish and hunt and has a Harley .Amen ,

04-12-2003, 02:24 AM	#11
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	Mine used to do that.....it was the radiator, but I knew it was the radiator because the fins were all mashed up and the previous owner had about half of the core blocked to keep it from leaking. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

04-12-2003, 06:02 AM	#12
A.P. Black 72 Chevy Join Date: May 2002 Location: Los Angeles, California Posts: 662	My truck would over heat and what I did was replace the thermostat and sent the rad to get clean. It now working fine. Good luck with your problem. A.P.

04-12-2003, 11:05 PM	#13
69 XCamper Registered User Join Date: Feb 2003 Location: Lake In The Hills, IL Posts: 28	update OK, I pulled out the thermostat and now it runs very cool. The radiator seems to be flowing fine. I'll pick up a new thermostat and drop it in tomorrow. __________________ 69 Chevy C20 (stock & waiting) 69 Datsun Roadster SPL311 (still waiting for resto) 02 Hyundai Elantra GT 00 Ford Expedition 99 Coleman Utah Lake In The Hills, Illinois

04-13-2003, 09:20 AM	#14
Blue Beard Registered User Join Date: Jan 2003 Location: Washington State Posts: 8,834	Another satisfied member................ __________________ 1970 Chev CST 2003 Harley Fatboy 1975 Chevrolet Step Van 1956 Chev Bel Air 1977 Blazer 2WD For Sale $3000.00 1978 Blazer 2WD For Sale $7000.00 1978 Silverado 2005 Monte Carlo



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