71 running hot, please help
Thread Starter
Burning Brakes
Joined: Mar 2006
Posts: 1,036
Likes: 2
From: Huntingburg Indiana
71 running hot, please help
I have a 71 with a 350 and 4 speed. I recently rebuilt the engine with 9.8:1 compression, lunati cam, mallory e-spark, milodon high flow water pump and thermostat, and direct drive fan. It was about 90 degrees today and I was in slow traffic. The temp got around 230. When
I could reach higher speeds, the temp would come down, but not cool enough. I don't think it's related to engine speed because I was running about 3000 rpm and the temp got lower than when I was at idle. I used a 160 thermostat. All of the radiator seals are in place, the radiator is clean, timing is correct and jetting is perfect. I re-used my radiator hoses because they looked okay. I did notice that the lower hose didn't have the spring. Should a 71 use one? During the little bit I drove it last summer, it got a little warm then too. Could there still be air in the system? I heard these can be tricky to bleed. Is the lower hose spring the problem? Please help. I am taking my car to bowling green next weekend for the hot rod reunion and if I need parts I want to order them now. Thanks a lot.
I could reach higher speeds, the temp would come down, but not cool enough. I don't think it's related to engine speed because I was running about 3000 rpm and the temp got lower than when I was at idle. I used a 160 thermostat. All of the radiator seals are in place, the radiator is clean, timing is correct and jetting is perfect. I re-used my radiator hoses because they looked okay. I did notice that the lower hose didn't have the spring. Should a 71 use one? During the little bit I drove it last summer, it got a little warm then too. Could there still be air in the system? I heard these can be tricky to bleed. Is the lower hose spring the problem? Please help. I am taking my car to bowling green next weekend for the hot rod reunion and if I need parts I want to order them now. Thanks a lot.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
Get that 160 stat out of there! You {must} run at least a 180. That high flow water pump is not the best for a overheating car either. The water has to be held back in the engine to allow the radiator to cool it. I know the prevailing opinion on this and other forums is to sware that a 160 is the way to fly. Wrong! What happens is that it`s cool at first, but as the engine gets hotter this hot water is suppost to be cooled by the radiator. Well it then circulates faster that the radiator can recover. The result is all the components to have a overheated engine condition. At speed the air will help cool it, but it`s at the lower slow traffic speeds that cause the problem.`Dont take it to the Woodword Dream Cruise or it will be along side of the road like so many others with the same problem, boiling over. 
Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
Ditto with Ironcross....that 160 Tstat isn't helping. Sounds to me like the water isn't spending enough time in the rad to adequately cool it. As for the lower hose spring, let it get hot then pull over, open the hood and rev the motor to about 3500 rpm or so and see what it's doing- if it isn't collapsing you should have no problem there. Also make sure your fan clutch is working properly- your fan should be pulling mucho air at idle. Godspeed
Le Mans Master
Joined: Aug 2000
Posts: 6,273
Likes: 14
From: Austin TX
Be sure your fan shroud is sealed against the back of the radiator and that your chin spoiler is in place. Also be certain that you have the seal at the top of the radiator frame that seals against the underside of the hood.
Missing seals allows air to move around the radiator rather than thru it.
Missing seals allows air to move around the radiator rather than thru it.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Originally Posted by Ironcross
Get that 160 stat out of there! You {must} run at least a 180. That high flow water pump is not the best for a overheating car either. The water has to be held back in the engine to allow the radiator to cool it. I know the prevailing opinion on this and other forums is to sware that a 160 is the way to fly. Wrong! What happens is that it`s cool at first, but as the engine gets hotter this hot water is suppost to be cooled by the radiator. Well it then circulates faster that the radiator can recover. The result is all the components to have a overheated engine condition. At speed the air will help cool it, but it`s at the lower slow traffic speeds that cause the problem.`Dont take it to the Woodword Dream Cruise or it will be along side of the road like so many others with the same problem, boiling over.
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Heel & Toe
Joined: Dec 2003
Posts: 15
Likes: 0
From: Southern California CA
Do you have power pulleys? (which would make the car run around town)If you do not I would tell you should get a new temp sender from Lectric not from a local auto store because they are not correct. With the lower radiator hose the system should be under pressure so the hose should not colapse if it does you have leak somewhere.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by dwncchs
I dont get your thinking--when an engine gets to 200 the 180 and the 160 are wide open and wont close again until the temp.drops back to 180 or 160--right?
A thermostat is exactly that...If there was no thermostat, then I would buy the "not holding the coolant in the radiator long enough" scenario.
Burning Brakes
Joined: Aug 2005
Posts: 1,126
Likes: 0
From: Hudson Falls, N.Y. 76 Vette Modified L-48
Originally Posted by dwncchs
I dont get your thinking--when an engine gets to 200 the 180 and the 160 are wide open and wont close again until the temp.drops back to 180 or 160--right?
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
It's also common to have defective thermostats.
Try it without one, just to test, and go back with a quality one of no less than 180.
With all the engine work you did, I assume your block water jackets are clean. (You had it boiled out?)
You say your rad is clean. It can be severely plugged and look clean at the openings. Should be flow tested.
Flush system at minimum also to test.
Try it without one, just to test, and go back with a quality one of no less than 180.
With all the engine work you did, I assume your block water jackets are clean. (You had it boiled out?)
You say your rad is clean. It can be severely plugged and look clean at the openings. Should be flow tested.
Flush system at minimum also to test.
Safety Car
Joined: Mar 2005
Posts: 3,503
Likes: 2
From: Raleigh NC
There's another good reason for not running a 160F thermostat--the EFE valve.
The TVS (thermal vacuum switch) opens the EFE butterfly valve at 180F--anytime the coolant is below 180F, the right side of the exhaust system is practically shutdown. This is also called the heat riser valve. Note the temperature marking on the bottom of the TVS:
The TVS (thermal vacuum switch) opens the EFE butterfly valve at 180F--anytime the coolant is below 180F, the right side of the exhaust system is practically shutdown. This is also called the heat riser valve. Note the temperature marking on the bottom of the TVS:
Last edited by PhotoVette1; Jun 10, 2006 at 05:49 AM.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by PhotoVette1
There's another good reason for not running a 160F thermostat--the EFE valve.
The TVS (thermal vacuum switch) opens the EFE butterfly valve at 180F--anytime the coolant is below 180F, the right side of the exhaust system is practically shutdown. This is also called the heat riser valve.
The TVS (thermal vacuum switch) opens the EFE butterfly valve at 180F--anytime the coolant is below 180F, the right side of the exhaust system is practically shutdown. This is also called the heat riser valve.
Last edited by Bob Onit; Jun 10, 2006 at 05:50 AM.
Melting Slicks
Joined: Mar 2006
Posts: 3,342
Likes: 7
From: Connecticut
Originally Posted by kb2fzq
Right!....the T-stat is ONLY there to reserve heat in the coolant to give you heat in the cabin during cold weather...
If you found an old "Heater delete" car it would still have a thermostat
Burning Brakes
Joined: Aug 2005
Posts: 1,126
Likes: 0
From: Hudson Falls, N.Y. 76 Vette Modified L-48
Originally Posted by Bob Onit
Nah, It regulates the temp of the coolant.. you need a thermostat..I buy mine from the dealer, wont trust chinese crap when it comes to.... well anything
If you found an old "Heater delete" car it would still have a thermostat
If you found an old "Heater delete" car it would still have a thermostat
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
You might try putting a clutch back on the fan. I know this seems like its opposite of what you need but sometimes when running a direct fan on the freeway, the fan is causing too much turbulance to the high speed air trying to blow through the radiator and it causes a cooling problem at high speed. You may also try a smaller water pump pulley to slow the water circulation. 180 stat is not going to allow it to run cooler if the cooling system itself is only capable of keeping the water at 190-200*. It will make no difference. Sometimes running a 195* stat will though because the system is capable of maintaining 195* therefore the stat will be opening and closing more often, that is restricting the flow through the radiator and allowing more cooling time in the radiator. There is nothing wrong with a small block running 195-210* at idle as long as it holds constant there. You really don't want it getting over 210* though.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Originally Posted by bondoboy
I have a 71 with a 350 and 4 speed. I recently rebuilt the engine with 9.8:1 compression, lunati cam, mallory e-spark, milodon high flow water pump and thermostat, and direct drive fan. It was about 90 degrees today and I was in slow traffic. The temp got around 230. When
I could reach higher speeds, the temp would come down, but not cool enough. I don't think it's related to engine speed because I was running about 3000 rpm and the temp got lower than when I was at idle. I used a 160 thermostat. All of the radiator seals are in place, the radiator is clean, timing is correct and jetting is perfect. I re-used my radiator hoses because they looked okay. I did notice that the lower hose didn't have the spring. Should a 71 use one? During the little bit I drove it last summer, it got a little warm then too. Could there still be air in the system? I heard these can be tricky to bleed. Is the lower hose spring the problem? Please help. I am taking my car to bowling green next weekend for the hot rod reunion and if I need parts I want to order them now. Thanks a lot.
I could reach higher speeds, the temp would come down, but not cool enough. I don't think it's related to engine speed because I was running about 3000 rpm and the temp got lower than when I was at idle. I used a 160 thermostat. All of the radiator seals are in place, the radiator is clean, timing is correct and jetting is perfect. I re-used my radiator hoses because they looked okay. I did notice that the lower hose didn't have the spring. Should a 71 use one? During the little bit I drove it last summer, it got a little warm then too. Could there still be air in the system? I heard these can be tricky to bleed. Is the lower hose spring the problem? Please help. I am taking my car to bowling green next weekend for the hot rod reunion and if I need parts I want to order them now. Thanks a lot.