Thread: 318 running hot

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Remember ..........when using a shroud with a belt driven fan....you only want the fan to be no more than 3/4"-1" inside the shroud. If you have the fan too far into the shroud, you defeat the purpose of the fan pulling max air thru the rad.

I never had any problem with that Mikej. It might take a little longer to warm up in the winter but that was it.
It always ran with in about 5 degrees no matter what the out side temps were.
Before that it would over heat because it was over bored with about 10.5 to 1 compression.
And that was running a 160 stat, I just had really good luck with them.
Kurt

I've been pondering the function of a fan and shroud.

Seems to me, the fan isn't pulling the air only, but is also slinging it out along the circumference.

As such, it seems to me the fan is most efficient if placed at the edge of the shroud?

If so, then the shroud protects fingers at the cost of some air flow.

Originally Posted by firebird77clone

I've been pondering the function of a fan and shroud. Seems to me, the fan isn't pulling the air only, but is also slinging it out along the circumference. As such, it seems to me the fan is most efficient if placed at the edge of the shroud? If so, then the shroud protects fingers at the cost of some air flow.

Position the fan blades halfway in and halfway out of the shroud opening.
If you're using a vee belt system, observe the fan blades and make certain the fan is for a vee belt system, not a serpentine system. If you stand in front of the radiator, bend over and look down on the fan blade(s). If you consider that the firewall is North and where you are standing is South, the orientation of the blades should be Northwest to Southeast with the concave side (hollowed out side) of the blades toward the motor.
If using a serpentine system, the fan blade orientation should be Southwest to Northeast with the concave side of the blades toward the motor. If you flip the fan over and install it backwards, it will still move air in the direction it was meant to move air, but not as efficiently because the concave side of the blades will be toward the radiator. I predict that everyone using a mechanical fan system will go out and check this for themselves if they didn't know what I just wrote.
What cam are you using? You may need more initial spark advance.

Do you have any idea what the piston deck height was set at? How about squish? How about gasket thickness? If the shop used the wrong intake gaskets, they may have also used the wrong head gaskets. Aluminum heads require a pre-flattened fire ring to prevent brinelling the surface of the heads. The fire ring can imprint into the aluminum if it's wrong for the aluminum heads and you will have to take a skim cut on them to remove the pressed-in ring before you can bolt them onto another motor.

For the education of some of you on here (some of you already know this), Smokey Yunick explained the overheating problem with too thin cylinder walls due to excessive overboring. I'll paraphrase....
The piston rings in a motor do not slide smoothly up and down the cylinder walls, they move along with little, jerky actions, sort of like skidding. As they skid on the wall, little harmonics (vibrations) are generated. If the walls are thick, then there is enough meat to cancel out these vibes before they can get through the cylinder wall to the cooling water on the other side of the wall. If the walls are very thin, with insufficient meat to cancel the harmonics, then they are directed at the cooling water where they separate the water into little air bubbles. These bubbles cling to the surface of the cylinder on the water side and prevent cooling water from getting to the metal to remove heat. Result: an overheating motor. THANKS SMOKEY (RIP).

Are you using a stainless steel spring in the lower radiator hose? That will prevent it collapsing when the water pump pulls hard and the hose is hot.

What were the cylinder pressure readings that the shop took?

ah, I wish I had the answers to all your specific questions, but I just gave the shop too much reign.

I hope to god Summit sent the correct head gaskets, as the intake gaskets they sent were wrong type, and failed.

Just picked up the car Friday, and the overheat problem is gone. I still plan to add an oil cooler when I relocate the oil filter, it is almost touching the headers.

I have picked up an old clutch fan assembly, and will look into installing it with a shroud. Although it is cooling ok now, in 70 degree weather, I question if it will cool ok in triple digits when summer is here.

oh hey, tech. if you could please explain, why does a bad intake gasket cause over heating?

the bubbles on the cylinders is a new one to me. I thought the thinner walls simply allowed more heat to get into the water.

Originally Posted by firebird77clone

oh hey, tech. if you could please explain, why does a bad intake gasket cause over heating?
the bubbles on the cylinders is a new one to me. I thought the thinner walls simply allowed more heat to get into the water.

Short of losing all the cooling water and overheating, I don't know. I suspect that there was more than one problem going on and the shop fixed everything that was wrong, including the cause of the overheating.

Thank you. That is how I'm feeling about it.

To me, the only thing the intake gasket issue explains is the water in the oil.

This thread is a bit old but still in 2012. I am excited to finally get my motor running after years of delays. It is a rebuilt 350 SBC two-bolt main '76 Corvette block with 882 heads shaved to 9:1 compression ratio and 0.030 rebore. I have a 15" flexfan on a Zip water pump setup and it overheats in about 15 minutes of idle at 1100 rpm with all Prestone in the Speedway Cobra radiator in a '29 Ford shell with a bottom cooler section for the trans. I have drilled one 3/16" bypass hole in the 160 degree thermostat, should I drill more bypass holes as well as add a shroud or add a restrictor washer or will just a shroud cool it? I like the idea of a restrictor washer but maybe holes in the thermostat plate can do the same thing? I would like to avoid a shroud if possible because it is really tight inside the '29 shell and I plan to run a stock Model A hood.

Don Shillady
Retired Scientist/Teen Rodder

Originally Posted by Don Shillady

This thread is a bit old but still in 2012. I am excited to finally get my motor running after years of delays. It is a rebuilt 350 SBC two-bolt main '76 Corvette block with 882 heads shaved to 9:1 compression ratio and 0.030 rebore. I have a 15" flexfan on a Zip water pump setup and it overheats in about 15 minutes of idle at 1100 rpm with all Prestone in the Speedway Cobra radiator in a '29 Ford shell with a bottom cooler section for the trans. I have drilled one 3/16" bypass hole in the 160 degree thermostat, should I drill more bypass holes as well as add a shroud or add a restrictor washer or will just a shroud cool it? I like the idea of a restrictor washer but maybe holes in the thermostat plate can do the same thing? I would like to avoid a shroud if possible because it is really tight inside the '29 shell and I plan to run a stock Model A hood.

Don Shillady
Retired Scientist/Teen Rodder

Don,
First of all, why are you tagging your question onto an old thread instead of starting a new one? You will get a lot more attention if you start a thread listing your specific problem and your name in the by-line because people will look at this one and think it's old news already closed.

Don't drill any more holes in your thermostat or you might as well drop it in the trash can and buy a new one. The hole you drilled serves one purpose, to allow air to vent from the system as you fill it with coolant to make the job easier and less of a hassle. Without the hole the thermostat will be closed, trapping air in the block, and the only way to get it out is to start the engine, get it up to temp where the thermostat opens, and "burp" the system. In my experience this was a messy and frustrating process as the air bubble would burp big, pushing coolant out the open cap, and making a big mess. No more holes.

The missing shroud is your problem. At idle the fan is going to pull air from the path of least resistance, and that is around the tips of the blades, behind your radiator. Sure, you get some flow through the radiator, but you're losing efficiency. If you're running an electric fan, your shroud can be as simple as a sheet of aluminum with the edges turned down, and a hole a bit smaller than your fan diameter. Mine is 1/2" thick, fits over the back edge of the radiator frame, and adds 1/8" to the overall thickness. If I pull in hot it will cool while idling to just above the thermostat set point within three to five minutes. If you're running a mechanical, Tech pointed out the fitment for them above.

Hello Rodger,

Thanks for the explanation of the air hole which was suggester to me by a guy who builds Cobras but mostly with Ford 351W engines (John York). At this point I am the main consumer of Prestone in the area and have wasted several gallons but I do have a blank plastic shroud which I can install. I am concerned that with my high Zip water pump a shroud may cover the air flow at the bottom of the radiator where the trans cooler is? As to the post, I have been on and off this site with long intervals away due to other tasks and I have not kept up with the changes in the system. At this point I simply have not figured out how to start a new thread and I previously asked for a tutorial after your correction on the 1910 T speedster insert into the Drag Nationals. Can you just give me a hint at how to start a new thread?

Don Shillady
Retired Scientist/Teen Rodder

Originally Posted by Don Shillady

Hello Rodger,

Thanks for the explanation of the air hole which was suggester to me by a guy who builds Cobras but mostly with Ford 351W engines (John York). At this point I am the main consumer of Prestone in the area and have wasted several gallons but I do have a blank plastic shroud which I can install. I am concerned that with my high Zip water pump a shroud may cover the air flow at the bottom of the radiator where the trans cooler is? As to the post, I have been on and off this site with long intervals away due to other tasks and I have not kept up with the changes in the system. At this point I simply have not figured out how to start a new thread and I previously asked for a tutorial after your correction on the 1910 T speedster insert into the Drag Nationals. Can you just give me a hint at how to start a new thread?

Don Shillady
Retired Scientist/Teen Rodder

Don,
You bet! Let's start assuming you're in one of the specific forums:
1. Click the "Forum" tab at the upper left, just below the CHR logo. (I almost always have to hit it twice, because the first time it comes up telling me that I don't have permission to go there , then the second hit works.)
2. Scroll down past the random pictures, and you'll see areas of the forum, "Hot Rod Stuff For Sale", "All Hot Rod Talk Area", etc. You want to be in "All Hot Rod Talk Area".
3. Pick the forum you want to add your thread to, and click that name, let's say you pick "Hot Rod Talk" for general discussions. Click the bold "Hot Rod Talk" name.
4. Now you're in that forum, and about mid screen on the left, below the forum name "Hot Rod Talk" is a box, "New Thread". Press that box, and you'll get the Message Box where you enter your title, and below that the text. Once you're done scroll down below the pale blue area and see two boxes to the right, "Submit New Thread" and "Preview Post". Hit "Submit New Thread" and you're done! If you want to see how it's going to look just hit the "Preview Post" button, but don't forget to go back and hit "Submit New Thread" after you're happy with it - I've lost several when I forget, go back to the forum and then wonder why my work was lost

Hope that all makes sense, Don. Give it a shot! Oh yeah, if you want to add pictures to that new thread just scroll down to the next pale blue area, "Additional Options" and use the "Manage Attachments" feature, which you've already mastered!! Good luck!

A new thread would have been better, but I appreciate the interest.

My project is in limbo. Car just got shipped back to GA, and I have my little shop and can work on it at my leisure, in between job interviews.

I picked up an assortment of restrictors, but at the moment using a gutted t stat. I have the mechanical fan, but need to pick up the studs. Thinking of fabricating a shroud with wire frame and fiberglass.

Also need to instal the sensor for the mechanical temp sensor, and get the guages working so I can have a better idea of what's going on.

Water plain will run the coolest temperatures, 100% Prestone is ineffective. Prestone's purpose is to keep water from freezing, a side benefit and small one is it will raise the boiling point of water somewhat. So if it were my car I use the proper ratio of Prestone and water and try again, maybe get a 180 or 190 stat too raise the warm up temp threshold. Possibly the 160 opens to soon and acts as if no stat were in the system.

Shroud - Speedway Motors, America's Oldest Speed Shop

As to the transmission an auxiliary cooler is easily plumed, also if you are running a stock stall converter you will more then likely be fine. You mentioned the shroud you have might cover some of the back side of the lower radiator tank. The air flow could just go around and actually provide some additional cooling. If you have room consider an electric fan many have shrouds built into the design, just a couple of ideas to chew on.

Building a fiberglass shroud, here a good article and reference.
http://www.crankshaftcoalition.com/w...ass_fan_shroud

If you are boiling over at idle, you're not move the air thru the radiator. Need a shroud. Your timing is retarded to much. Causing the motor to over heat. You need an overflow tank. You are over filling the Radiator. Just a few ideas.