water pump
Melting Slicks
Joined: Jul 2004
Posts: 2,867
Likes: 195
From: Maryland
For the engine to run cool @ idle you need about 26* of idle timing. Idle timing is defined as the sum of the initial timing and the timing provided by the VAC. Sounds like the vacuum fitting for the VAC is ported or is not providing sufficient vacuum to fully deploy the VAC. You also might not have the correct VAC for the idle vacuum. There three VAC for Chevrolet engines :
B22 - all base SB or optional SB with base engine camshaft as long as a manual trans. is fitted. 16*@15 " Hg
B20 - all big block, all SB with auto trans, L-79, L-46; L-82w/ manual trans 16* @ 12" Hg
B28 - all SB with mechanical lifter camshafts, L-82 with auto trans 16* @ 8" Hg
B22 - all base SB or optional SB with base engine camshaft as long as a manual trans. is fitted. 16*@15 " Hg
B20 - all big block, all SB with auto trans, L-79, L-46; L-82w/ manual trans 16* @ 12" Hg
B28 - all SB with mechanical lifter camshafts, L-82 with auto trans 16* @ 8" Hg
Last edited by Donald #31176; Jun 8, 2008 at 10:09 AM.
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
Either the can isn't working or you have the wrong vacuum can. If you went by the auto parts store computer but you have mods to the motor, including a different cam you probably have the incorrect vacuum cannister that you need.
Again, get a vacuum gauge and measure the vacuum your motor is producing at idle. You than need a vacuum can that will bring in all of it's advance about 2" of vacuum BELOW the amount that your motor is producing.
Tell us after measuring your vacuum level at idle what it is and we can help you with the correct vac. adv. can to buy.
Burning Brakes
Joined: Aug 2001
Posts: 1,104
Likes: 1
From: Frederick Md
Good afternoon
my 66 327/300 has been running hot at idle. I've been through everything on the board (timing, fan clutch, engine/radiator flush). Only things I haven't touched are water pump and radiator. It's fine at speed so I'm thinking not the radiator.
I was looking at water pumps at Advance Auto - they have everything from a $40 to a $200 one. I'm sure the higher $$$ ones push more coolant but I'm not sure they're worth the cost difference. I'm not worried about originality for judging.
What do y'all use? Anything to know? My car has had a little bit of work done (heads, intake, carb, cam and headers) but it's not drastically modified.
I'd appreciate your input.
Thanks
Bryan
my 66 327/300 has been running hot at idle. I've been through everything on the board (timing, fan clutch, engine/radiator flush). Only things I haven't touched are water pump and radiator. It's fine at speed so I'm thinking not the radiator.
I was looking at water pumps at Advance Auto - they have everything from a $40 to a $200 one. I'm sure the higher $$$ ones push more coolant but I'm not sure they're worth the cost difference. I'm not worried about originality for judging.
What do y'all use? Anything to know? My car has had a little bit of work done (heads, intake, carb, cam and headers) but it's not drastically modified.
I'd appreciate your input.
Thanks
Bryan
I use Stewart stage one pumps, they make a direct replacement pump that is much better than a stock pump and used with the correct thermo works quite nice.
The 62 has a new Dewitt radiator with the fan assembly built on, no shroud and no fan on the motor, no problems.
Drifting
Joined: Apr 2001
Posts: 1,401
Likes: 9
From: Holly Springs, Nort Cackalacky / Jupiter, Florida
In this picture I noticed that where I would expect a bypass hose to be connected is plug'd on the water pump side and has a heat sender unit on the front of the intake.
Not saying this is the problem, but I wanted to know what is the purpose of the bypass?
I have a water pump/intake that uses a bypass and never thought about it's purpose/function.
Thanks,
RK
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
In this picture I noticed that where I would expect a bypass hose to be connected is plug'd on the water pump side and has a heat sender unit on the front of the intake.
Not saying this is the problem, but I wanted to know what is the purpose of the bypass?
I have a water pump/intake that uses a bypass and never thought about it's purpose/function.
Thanks,
RK
Not saying this is the problem, but I wanted to know what is the purpose of the bypass?
I have a water pump/intake that uses a bypass and never thought about it's purpose/function.
Thanks,
RK
The bypass reduces cavitation of the coolant at higher RPM's.
It is odd to have the temp sender unit with that placement on the intake though
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
Hard to tell from the photo but as others have said, the fan blade doesn't look far enough into the shroud. The blade appears to be too small diameter and the blade pitch looks shallow. I'd look in this area for the cause of your problem.
Engine timing. You're wasting your time looking at lack of vacuum advance timing as the root cause of any overheating. May be a contributor but that alone won't cause it. The '63-early '64 fuelies had little or no vacuum advance at idle and they'd idle all day long without overheating. All the advance you had on them was 10-12 degrees, total.
Engine timing. You're wasting your time looking at lack of vacuum advance timing as the root cause of any overheating. May be a contributor but that alone won't cause it. The '63-early '64 fuelies had little or no vacuum advance at idle and they'd idle all day long without overheating. All the advance you had on them was 10-12 degrees, total.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
There's absolutely no need for any of the "whizbang" water pumps - the stock water pump will work just fine, and the water pump is hardly ever the cause of a cooling problem (unless the fins on the impeller are corroded away).
Can you define "running hot at idle"? Have you checked it at the thermostat housing with an I.R. gun so you know what the temp gauge is really telling you? Does it "puke" coolant out of the overflow hose when idling?
"Running hot" at idle is almost always either an airflow issue (radiator not sealed to the support, shroud not sealed to the radiator, fan clutch worn out) or an ignition timing issue (initial timing retarded, vacuum advance not working or connected to the wrong vacuum source). Check these basics before tearing into the water pump. See my feature article on cooling in the current (August) issue of "Corvette Enthusiast" magazine.
Can you define "running hot at idle"? Have you checked it at the thermostat housing with an I.R. gun so you know what the temp gauge is really telling you? Does it "puke" coolant out of the overflow hose when idling?
"Running hot" at idle is almost always either an airflow issue (radiator not sealed to the support, shroud not sealed to the radiator, fan clutch worn out) or an ignition timing issue (initial timing retarded, vacuum advance not working or connected to the wrong vacuum source). Check these basics before tearing into the water pump. See my feature article on cooling in the current (August) issue of "Corvette Enthusiast" magazine.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 108
Likes: 0
From: Pinehurst, NC
What should I look for with fan clutch? I just got this one from Advance or one of those local shops. As i recall it looked like the original. It was overheating before I replaced that.
On Zip website I see a thermostatic and torque limiting. About $75 difference. Does it matter?
My fan appears to measure about 16.5" across. Far as I know it's original. Trying to find out if the old man knows any different. You say they should be about an inch bigger?
RE: temp sending unit - If i remember right that's the best place we had left to put it. Dad bought the intake from ebay. Supposed to be from a 365hp car. Where should it be?
RE: vacuum input - I'll look the carb over more closely. That was the most likely place when we put the carb on.
I do not have an IR gun. Going by the dash gauge. It continues to rise until I kill the engine or start moving. It does not puke coolant. I have heard it gurgling but never come out.
I'm going to try the paper on the radiator as well. It should always stick to the radiator due to fan sucking air through?
I'll try to pick up a vacuum gauge in near future as well. What should I look for with that?
Thanks for the input. I love when it runs right but here in SC if it sits in traffic it gets hot real quick!
Bryan
On Zip website I see a thermostatic and torque limiting. About $75 difference. Does it matter?
My fan appears to measure about 16.5" across. Far as I know it's original. Trying to find out if the old man knows any different. You say they should be about an inch bigger?
RE: temp sending unit - If i remember right that's the best place we had left to put it. Dad bought the intake from ebay. Supposed to be from a 365hp car. Where should it be?
RE: vacuum input - I'll look the carb over more closely. That was the most likely place when we put the carb on.
I do not have an IR gun. Going by the dash gauge. It continues to rise until I kill the engine or start moving. It does not puke coolant. I have heard it gurgling but never come out.
I'm going to try the paper on the radiator as well. It should always stick to the radiator due to fan sucking air through?
I'll try to pick up a vacuum gauge in near future as well. What should I look for with that?
Thanks for the input. I love when it runs right but here in SC if it sits in traffic it gets hot real quick!
Bryan
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Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
my '65 is the 365hp motor with the correct intake.
you can see the temp sender location right next to the fuel filter
as for your fan, don't know if the '66's were different but the '65 fan has an overall diamter of 17 1/8". 5 blades.
On the fanclutch, again, not sure if the '66's were different, but the '65 used thermostatic type clutches.
you can see the temp sender location right next to the fuel filter
as for your fan, don't know if the '66's were different but the '65 fan has an overall diamter of 17 1/8". 5 blades.
On the fanclutch, again, not sure if the '66's were different, but the '65 used thermostatic type clutches.
Last edited by BarryK; Jun 8, 2008 at 07:58 PM.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
The current replacement fan clutch (which has a longer shaft and will position the fan correctly half-in/half-out of the rear edge of the shroud) is GM #3916141; most of the Corvette vendors sell it, and GMPartsDirect.com also has it.
Le Mans Master
Joined: Jul 2003
Posts: 6,808
Likes: 24
From: Westport CT
I can't help but notice that it looks like you have the original rad in there (pn 3155316, 66D date code); that's an expensive item but a 42 year old rad might not be doing the same job today as it did 42 years ago [food for thought]:
Last edited by ctjackster; Jun 9, 2008 at 12:45 PM.
Melting Slicks
Joined: Nov 2002
Posts: 2,460
Likes: 5
From: Wheaton IL
that means your vacuum advance is only adding 2º at idle. It should be adding in 15º or 16º of advance at idle.
Either the can isn't working or you have the wrong vacuum can. If you went by the auto parts store computer but you have mods to the motor, including a different cam you probably have the incorrect vacuum cannister that you need.
Again, get a vacuum gauge and measure the vacuum your motor is producing at idle. You than need a vacuum can that will bring in all of it's advance about 2" of vacuum BELOW the amount that your motor is producing.
Tell us after measuring your vacuum level at idle what it is and we can help you with the correct vac. adv. can to buy.
Either the can isn't working or you have the wrong vacuum can. If you went by the auto parts store computer but you have mods to the motor, including a different cam you probably have the incorrect vacuum cannister that you need.
Again, get a vacuum gauge and measure the vacuum your motor is producing at idle. You than need a vacuum can that will bring in all of it's advance about 2" of vacuum BELOW the amount that your motor is producing.
Tell us after measuring your vacuum level at idle what it is and we can help you with the correct vac. adv. can to buy.
Brian
Le Mans Master
Joined: Aug 2005
Posts: 6,541
Likes: 1,975
From: Temple Terrace Florida
Hot
I have a 66 small block and I added a rubber upper rad. rubber seal. The seal goes over the top of the shroud and the rad. It is held on by three or four clips. The seal is listed for big blocks and small blocks with AC. I also added a Dewitts alm. rad. Made all the difference in the world. You can find the seal at Long Island Corvettes section 26 of their catalog. Dr. Rebuild also has them listed. Jerry
Melting Slicks
Joined: Feb 2007
Posts: 2,937
Likes: 163
From: OP Kansas
C2 of Year Finalist (appearance mods) 2019
This tells all, it seems everything works fine while driving so I still say put that fan half in and half out of the shroud by using a spacer and report back. This will be the fastest and cheapest fix you can try, if it doesn't work move on to other items mentioned.
Le Mans Master
Joined: Oct 2006
Posts: 7,596
Likes: 106
From: North Carolina "life is good"
2025 c3 ('68-'73) of the Year Finalist - Unmodified
Here is a pic of my mostly original 300 hp '66 ( I know al finned covers on a 300hp engine, but I like the looks) showing the fan sitting more into the shroud than yours. My shroud looks just like yours including the open square under the upper rad hose on the left side.
Race Director
Joined: Jul 2002
Posts: 11,593
Likes: 173
From: Clayton NC
I love how summer time and high temps bring out the over heating threads... BTW wish I had seen this a couple of days ago or if you had brought the car out to the Corvette show at Broadway at the Beach.. I just got home from 4 days at Myrtle Beach. I would have been glad to given it a once over.
As Brian has mentioned, check where you are getting you vac source from. Then Jack has noticed that it appears you have an original radiator. Both of these problems could be causing your situation. Dave
As Brian has mentioned, check where you are getting you vac source from. Then Jack has noticed that it appears you have an original radiator. Both of these problems could be causing your situation.
Dave
Instructor
Joined: Feb 2005
Posts: 243
Likes: 5
From: Leland, NC
Hi Dave,
Good to see you at Myrtle Beach. I have been reading this thread about the overheating. Mine was doin' it like crazy whenever I got stuck in that beach traffic.
I have the opposite situation, the fan is too far into the shroud based on the discussions at the show and here on the thread. How do I get it back out of the shroud? Is it possible I have the wrong fan clutch? I have sealed up the shroud during previous bouts of this condition. I had it all under control until I put the 383 in back in April - here we go again!
BTW, enjoyed meeting Mark, good guy.
Bob
Good to see you at Myrtle Beach. I have been reading this thread about the overheating. Mine was doin' it like crazy whenever I got stuck in that beach traffic.
I have the opposite situation, the fan is too far into the shroud based on the discussions at the show and here on the thread. How do I get it back out of the shroud? Is it possible I have the wrong fan clutch? I have sealed up the shroud during previous bouts of this condition. I had it all under control until I put the 383 in back in April - here we go again!
BTW, enjoyed meeting Mark, good guy.
Bob
Race Director
Joined: Oct 2005
Posts: 12,470
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
Doug
