How hot?!!
Senior User
Joined: Aug 2003
Posts: 152
Likes: 0
From: Maple Ridge BC Canada
How hot?!!
The extra 20 cfm is no problem, most wont flow what the manufacture say they will anyway. If you run a smaller carb 550 to 600 you can expect better throttle response, but will resrict HP and TQ at wide open throttle, so its a bit of a trade off. It just depends what your needs are.
Junk in the carb could be the source of the overheating problem(lean condition). Make sure your timing is set at 10 to 12 degrees. If its retarded it will pop thru the carb and run hot.
My truck ran hot at idle, but its a fairly agressive setup. I was able to solve my problem by replacing the stock 4 blade fan with an 18" stainless flex fan, I have no fan shroud.....Let us know how you make out.....D44HD
Junk in the carb could be the source of the overheating problem(lean condition). Make sure your timing is set at 10 to 12 degrees. If its retarded it will pop thru the carb and run hot.
My truck ran hot at idle, but its a fairly agressive setup. I was able to solve my problem by replacing the stock 4 blade fan with an 18" stainless flex fan, I have no fan shroud.....Let us know how you make out.....D44HD
Post Fiend
Joined: Jun 2003
Posts: 8,209
Likes: 12
From: Black Hills of SD
How hot?!!
The shroud is a key element to avoiding over heating at low speeds. Running without a thermostat is not always good. Your engine needs one for two reasons. One is to maintain an operating temperature that will keep your engine warm enough to run right. And the other reason that evades some people is that without it the water may move through the radiator too fast to get cooled off, and can even cause a cavitation affect that will make bubbles in the water. In a circle track car, no thermostat is a sure fire boilover, and we have even had to underdrive the pulleys and slow the pump down to avoid the problem.
Also make sure you have all the air out of the system. To do this I always like to run the engine with the cap off until the t-stat opens and you can see the coolant circulate in the radiator. Some cars will push out a bunch of coolant before they burp. You can usually avoid this by taking your time on the initial fill. I usually start pouring in the coolant a half an hour or so before I plan to fire it up and top it off avery few minutes. After the t-stat has opened, I run it up to about 2500 while topping off the radiator and install the cap while at that rpm. Now it is full but it may push a little back out the overflow when you shut it off and it heat soaks.
Also make sure you have all the air out of the system. To do this I always like to run the engine with the cap off until the t-stat opens and you can see the coolant circulate in the radiator. Some cars will push out a bunch of coolant before they burp. You can usually avoid this by taking your time on the initial fill. I usually start pouring in the coolant a half an hour or so before I plan to fire it up and top it off avery few minutes. After the t-stat has opened, I run it up to about 2500 while topping off the radiator and install the cap while at that rpm. Now it is full but it may push a little back out the overflow when you shut it off and it heat soaks.
Junior User
Joined: Aug 2003
Posts: 54
Likes: 0
From: Polson, Montana
How hot?!!
Why not go with the cooler thermostat if you are worried about the heat? Also is your engine bored out at all? Is it still 390 cubic inches? This figures into the carb calculation. 5500 rpm is pretty high for a 390 unless you've made some major mods. For most applications a 600 is perfect. A 650 is great too but anything bigger is wasted gas and you're not going to get any extra performance unless you've made some pretty serious mods to the motor.
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Junior User
Joined: Jun 2002
Posts: 62
Likes: 0
From: Mid-Eastern US
How hot?!!
d44hd: Thanks, will let you know how all turned out. willowbilly3: I never planned to run without a thermostat as this can form acids in the engine and cause the metal to break down into particles that the filter can not possibly keep up with, it was only suggested that I try it simply to see if the thermostat might be faulty somehow. If you did not need a thermostat to control the engines temp. then the manufacturer would probably leave it out to save on cost. I do plan to find a shroud for it and I am running one of those five blade super cooling fans that is after market from a local performance shop. deputy1515: the cooler thermostat will not make my truck run any cooler if it is getting too hot to begin with, it will only make the thermostat open sooner. The heat will still build up to what it is now, maybe just a little slower. Once I find the problem, a cooler thermostat may be in order to maintain my particular setup, but thanks for the input.
Post Fiend
Joined: Jun 2002
Posts: 13,873
Likes: 3
From: Atlanta GA
How hot?!!
> What is your folks opinion of the flex fans
I replaced my solid fan (no fan clutch) with a flex fan for $20 from Autozone. Except cutting my finger on the blade during installation it is okay. Note to self - do not turn blade with unprotected hand to get at next bolt hole.
They make a kind of whirling noise as RPMS change. If I was not running dual Cherry bombs it might be more annoying.
I am getting better gas mileage, though that might be because the old one was on backwards! Cooling is about the same.
I replaced my solid fan (no fan clutch) with a flex fan for $20 from Autozone. Except cutting my finger on the blade during installation it is okay. Note to self - do not turn blade with unprotected hand to get at next bolt hole.
They make a kind of whirling noise as RPMS change. If I was not running dual Cherry bombs it might be more annoying.
I am getting better gas mileage, though that might be because the old one was on backwards! Cooling is about the same.
Laughing Gas
Joined: Oct 1999
Posts: 1,165
Likes: 3
From: central Alberta
How hot?!!
Obviously, its really important to keep a close eye on those flex fans as cracks develop over time. Just keep that eye out of line with the fan while the engine's running 
They do throw blades from time to time, as one unfortunate owner of a #### truck found out sitting at the light ahead of me a couple of years ago. He started away and Pow! One nice big dent on the hood and a split lower rad hose.
mike
They do throw blades from time to time, as one unfortunate owner of a #### truck found out sitting at the light ahead of me a couple of years ago. He started away and Pow! One nice big dent on the hood and a split lower rad hose. mike
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Junior User
Joined: Jun 2002
Posts: 62
Likes: 0
From: Mid-Eastern US
How hot?!!
d44hd: carb is fixed after rebuild, no more backfiring. Removed thermostat and engine is still getting up to 210. I sprayed the radiator down with a water hose to get temp down to 190 before I shut it off. Probably still need to install the fan shroud. Maybe a good idea to install the steel 5 blade stock fan as well. I left the radiator cap off while running too, and the water is circulating nicely.
Senior User
Joined: Aug 2003
Posts: 152
Likes: 0
From: Maple Ridge BC Canada
How hot?!!
sounds right to me, you have eliminated the other possibles. A fan shroud sounds like the next step......D44HD
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Junior User
Joined: Jun 2002
Posts: 62
Likes: 0
From: Mid-Eastern US
How hot?!!
The 3 core rad I have now is brand new and if that isn't big enough then something is very wrong. I will check in the the electric fan although I am more comfortable with the conventional fans since they do not have any extra working parts that might go bad. Who would make one that you would recommend?
Senior User
Joined: Jul 2003
Posts: 163
Likes: 0
From: San Diego, CA(best weather in the world)
How hot?!!
I put a 7 blade flex fan on my 390 and it made a huge difference at idle. just make sure you get a steel one and not one of those cheap nylon or plastic ones. They have a tendency of breaking.
A radiator shroud is an absolute must! At idle the shroud ducts the air thru the radiator. Without it, your fan is all but useless. I wouldn't even think of running an engine without one.
Dennis
A radiator shroud is an absolute must! At idle the shroud ducts the air thru the radiator. Without it, your fan is all but useless. I wouldn't even think of running an engine without one.
Dennis
Senior User
Joined: Jul 2003
Posts: 193
Likes: 1
From: BC, Canada
How hot?!!
I was having cooling problems with mine when I put the new motor in and still using the stock 2-core rad. The rad would boil over just idling. Now with a 4-core rad, 195* thermostat and no shroud it sits at about 200* at idle. A fan is in the works still though.