Over Heating!!!!!!!!!!!!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

scooby3242 · 06-08-2006, 02:03 PM

Well I took my 71 out on the freeway for the first time ever and it started to over heat. I usually just drive around town. It has a 350 motor with a th350 tranny. The temp gauge normally reads 180 but after about 5 minutes on the freeway it climbed to 240. When I pulled over the tempature started to go down a bit. I have had a couple of people tell me that my truck had the smallest radiator they had ever seen on a 350 motor.Any ideas what the problem might be? Water pump,radiator, thermostat, fan clutch...Thanks

**1970 CST Short Wide** · 06-08-2006, 04:45 PM

Check them all, but my guess is the fan clutch

**truckdude239** · 06-08-2006, 05:04 PM

thermostat would be frist thing i try
post some pictures of the raditor and we can tell yal

67Fleet · 06-08-2006, 08:03 PM

Easiest thing to chk would be fan clutch, then I would try the thermostat next. I just got a new one for about 15 bucks.

cdowns · 06-08-2006, 09:45 PM

i'd take the rad cap off and look in the rad to see if it's filled with crud and deposits clogging the rad causing poor flow and bad heat transfer also to see if the antifreeze is freash

**Stocker** · 06-08-2006, 10:01 PM

There should be enough airflow at freeway speeds that the fan isn't needed, so I'm thinking that isn't the problem. If it were overheating at lower speeds, I would think the fan clutch may be the culprit... Same goes for fan shroud (or lack thereof).

So... how small is that radiator? Other than things already suggested, if your lower hose doesn't have the spring inside, it may be collapsing at increased rpms, blocking the flow of coolant.

pumpkin · 06-08-2006, 10:16 PM

Overheating on the freeway will not be caused by the fan. The possabilitys are, T stat, plugged or too small rad, or internall engine problem. Very, very rare would be water pump.

**clay68c10** · 06-08-2006, 10:23 PM

It's probably the radiator, a bad thermostat would give you problems around town too. Higher flow/rpm will magnify the problems from a clogged or too small rad. Too bad I just sold my extra 4-core.

Longhorn Man · 06-08-2006, 10:28 PM

Coolant flow is being restricted by a clog in the system, a worn water pump (not rare, I swap them all the time at work for this very reason) or maybe internal engine issues. (not a restriction)

The rad size isn't doing this. If that was the case, it would do it at lower speeds too. You have more air going through that rad when doing 60, than your fan could ever suck through it. That's why your engine temp would be 210 in town, and 195 on the open road. (I'm guessing at the numbers, but you get the idea)

pumpkin · 06-08-2006, 10:41 PM

Quote:

Originally Posted by Longhorn Man

Coolant flow is being restricted by a clog in the system, a worn water pump (not rare, I swap them all the time at work for this very reason) or maybe internal engine issues. (not a restriction)

The rad size isn't doing this. If that was the case, it would do it at lower speeds too. You have more air going through that rad when doing 60, than your fan could ever suck through it. That's why your engine temp would be 210 in town, and 195 on the open road. (I'm guessing at the numbers, but you get the idea)

Are they leaking, or rusted or slipping impellers? In my area, in my 32 years of being a mechanic, I've only come across two bad impellers out of a few hundred chevy water pumps. If you can give me more info that would be great.

Longhorn Man · 06-08-2006, 11:06 PM

I've seen many with the wobble and leaking weep holes that were overheating. And many that just don't pump anymore. We don't open them up, but I've been told anything from water pump case getting worn from loose bearings (but not weeping yet) and impellers eroding away.

We do at least one a month... not just chevys...but many are.

pumpkin · 06-08-2006, 11:47 PM

I've yet to see one that didn't pump ant more. And I have taken the back off of quite a few, under suspect, as I do see it on other engines, But only found a problem twice. Maybee its a climate, water thing. Its good stuff for me, as lately we've been have vehicles coming here from all over the states.

**Stocker** · 06-09-2006, 12:15 AM

Scooby -- when you find the problem.... let us know!

Wootdog · 06-09-2006, 04:23 AM

Did he say that he had a fan shroud on it? When I first got my 68 it had a two core and would overheat in traffic, but not going down the highway. I would suspect the thermostat. Kerry

dwaite72lnghrn · 06-09-2006, 06:11 AM

I don't have alot of info on this but if it is the first time ever in a long while on the freeway, Then it starts to overheat I would check the mechanical advance in the Dizzy it could have rusted full advance and now timing is wacked. Check your timing and mech advance.

Longhorn Man · 06-09-2006, 02:34 PM

A fan shroud is pretty important, but hinders airflow in the freeway.
Honestly, I guess I've been lucky, none of my trucks had them, and I never had a problem with overheating... in Tx or Ohio.

06-08-2006, 02:03 PM	#1
scooby3242 Registered User Join Date: Apr 2005 Location: Bedford, Tx Posts: 40	Over Heating!!!!!!!!!!!!! Well I took my 71 out on the freeway for the first time ever and it started to over heat. I usually just drive around town. It has a 350 motor with a th350 tranny. The temp gauge normally reads 180 but after about 5 minutes on the freeway it climbed to 240. When I pulled over the tempature started to go down a bit. I have had a couple of people tell me that my truck had the smallest radiator they had ever seen on a 350 motor.Any ideas what the problem might be? Water pump,radiator, thermostat, fan clutch...Thanks __________________ 1973 gmc swb

06-08-2006, 04:45 PM	#2
1970 CST Short Wide Senior Moment Join Date: Mar 2002 Location: Pittsburg Ca Posts: 4,111	Re: Over Heating!!!!!!!!!!!!! Check them all, but my guess is the fan clutch __________________ 1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565

06-08-2006, 05:04 PM	#3
truckdude239 Senior Member Join Date: Sep 2005 Location: Lewisville, Nc Posts: 10,233	Re: Over Heating!!!!!!!!!!!!! thermostat would be frist thing i try post some pictures of the raditor and we can tell yal __________________ David fuller Ase Certified Mechanic Click here to help support our board!! 1971 Chevy c-10 under going a 4.8l LSx swap Build Thread http://67-72chevytrucks.com/vboard/s...d.php?t=421305 2007 Honda Accord my daily 145kmiles 2002 Honda Accord 4 door With 330k(sisters car) 2005 toyota Avalon 228k( brothers car) 2002 Sububran 5.3 245k 2000 Tahoe 5.3l 378 General manager for Marco's Carwash & lube

06-08-2006, 08:03 PM	#4
67Fleet Outlandish Trends - FL Join Date: Jul 2005 Location: Orlando Posts: 1,396	Re: Over Heating!!!!!!!!!!!!! Easiest thing to chk would be fan clutch, then I would try the thermostat next. I just got a new one for about 15 bucks. __________________ -Bret 67 short-fleet sold!

06-08-2006, 09:45 PM	#5
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Over Heating!!!!!!!!!!!!! i'd take the rad cap off and look in the rad to see if it's filled with crud and deposits clogging the rad causing poor flow and bad heat transfer also to see if the antifreeze is freash __________________ 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

06-08-2006, 10:01 PM	#6
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,593	Re: Over Heating!!!!!!!!!!!!! There should be enough airflow at freeway speeds that the fan isn't needed, so I'm thinking that isn't the problem. If it were overheating at lower speeds, I would think the fan clutch may be the culprit... Same goes for fan shroud (or lack thereof). So... how small is that radiator? Other than things already suggested, if your lower hose doesn't have the spring inside, it may be collapsing at increased rpms, blocking the flow of coolant. __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

06-08-2006, 10:16 PM	#7
pumpkin Registered User Join Date: Apr 2006 Location: East Sooke B.C. Canada Posts: 543	Re: Over Heating!!!!!!!!!!!!! Overheating on the freeway will not be caused by the fan. The possabilitys are, T stat, plugged or too small rad, or internall engine problem. Very, very rare would be water pump.

06-08-2006, 10:23 PM	#8
clay68c10 Senior Member Join Date: Aug 2004 Location: Centennial, CO Posts: 2,935	Re: Over Heating!!!!!!!!!!!!! It's probably the radiator, a bad thermostat would give you problems around town too. Higher flow/rpm will magnify the problems from a clogged or too small rad. Too bad I just sold my extra 4-core. __________________ ClusterTruck: 68 C10 Bought in 89, wrecked in 03. Slow low $ rebuild started '17. 6.0 & TKO http://67-72chevytrucks.com/vboard/s...d.php?t=788602 93 K1500 Short Step, 350, NV4500, EBL flash ECU. Vortec heads & roller cam someday... 05 Jeep Wrangler Unlimited. 3” lift & 6-speed 02 E320 the insurance total “free car” 13 Tahoe LTZ

06-08-2006, 10:28 PM	#9
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Over Heating!!!!!!!!!!!!! Coolant flow is being restricted by a clog in the system, a worn water pump (not rare, I swap them all the time at work for this very reason) or maybe internal engine issues. (not a restriction) The rad size isn't doing this. If that was the case, it would do it at lower speeds too. You have more air going through that rad when doing 60, than your fan could ever suck through it. That's why your engine temp would be 210 in town, and 195 on the open road. (I'm guessing at the numbers, but you get the idea)

06-08-2006, 11:06 PM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Over Heating!!!!!!!!!!!!! I've seen many with the wobble and leaking weep holes that were overheating. And many that just don't pump anymore. We don't open them up, but I've been told anything from water pump case getting worn from loose bearings (but not weeping yet) and impellers eroding away. We do at least one a month... not just chevys...but many are.

06-08-2006, 11:47 PM	#12
pumpkin Registered User Join Date: Apr 2006 Location: East Sooke B.C. Canada Posts: 543	Re: Over Heating!!!!!!!!!!!!! I've yet to see one that didn't pump ant more. And I have taken the back off of quite a few, under suspect, as I do see it on other engines, But only found a problem twice. Maybee its a climate, water thing. Its good stuff for me, as lately we've been have vehicles coming here from all over the states.

06-09-2006, 12:15 AM	#13
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,593	Re: Over Heating!!!!!!!!!!!!! Scooby -- when you find the problem.... let us know! __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

06-09-2006, 04:23 AM	#14
Wootdog Senior Member Join Date: Jan 2001 Location: Virginia Beach, Va, USA Posts: 1,676	Re: Over Heating!!!!!!!!!!!!! Did he say that he had a fan shroud on it? When I first got my 68 it had a two core and would overheat in traffic, but not going down the highway. I would suspect the thermostat. Kerry __________________ 1969 Chevelle 1990 IROC Z Convertible 2002 Silverado LT

06-09-2006, 06:11 AM	#15
dwaite72lnghrn Registered User Join Date: Jun 2002 Location: central pa Posts: 1,525	Re: Over Heating!!!!!!!!!!!!! I don't have alot of info on this but if it is the first time ever in a long while on the freeway, Then it starts to overheat I would check the mechanical advance in the Dizzy it could have rusted full advance and now timing is wacked. Check your timing and mech advance. __________________ 72 longhorn c30 502BB/th400/fact air/4.11rear/ custom camper 72 bug(the better half's) under reconstruction 2009 HHR aqua blue 71 GMC k20 350/sm465 2009 Chevy hd3500 6.6 Victory Red crew cab dually Dave & Jeanne

06-09-2006, 02:34 PM	#16
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Over Heating!!!!!!!!!!!!! A fan shroud is pretty important, but hinders airflow in the freeway. Honestly, I guess I've been lucky, none of my trucks had them, and I never had a problem with overheating... in Tx or Ohio.



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