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I have a 72 convertible cougar and I have gone through and rebuilt the 351 Cleveland and now it constantly overheats. I had to bore the block 30 over. I went with a set of keith Black hyperutectic pistons and have a stock set of reman heads. The car is just for cruising and car show hopping so I built it keeping in mind the 4 dollars a gallon for gas. All the internals are pretty much stock specs so I can not understand why it wont stop overheating. I have tried electric fan(s), clutch and no clutch fans of all sorts of blade counts widths etc. I have a brand new aluminum radiator. I am running a 185 thermostat currently and have gone clear down to 160 with no change. The restrictor plate inside the thermostat area is there as well. If anyone can help or come up with any ideas that could help I would really appreciate it. :confused: By the way the car is running in an upwards of 230 degrees Fahrenheit. This will happen on a 70 degree day while in light stop light traffic.
 

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A few things i would check,
running too lean, timing too advanced, air pocket it cooling system.

Does the heater blow hot? do you see the water circulating in the radiator when its warmed up?
 

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When we advance the timing it will diesel really bad. If the timing is retarded a bit it wont stay running. The cooling system is circulating for sure so i dont believe we have any air pockets. we only have at most a 9.5:1 compression and are forced to run 91 octane and octane booster if its ran on the highway. Im wondering if going to an inline electric pump would be a better idea to use instead of the mechanical for the carburetor though its only a 650 edelbrock. Could advancing the cam shaft help as we just installed it to the center line? I have wondered for a while if a bad fuel to air mixture could cause such a drastic change in temperature or not.
 

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I would look for a vacuum leak first, a lean condition will make the engine run really hot and your specs shouldn't come close to causing a heating problem. I would then look at the amount of vacuum advance and total advance you are getting, you shouldn't have to run that much octane at cruise rpm down the highway at 9.5:1. Any chance you got a head gasket in upside down? Had a friend do that on a 400M and it overheated brutally. Last resort would be checking the cam timing, if you degreed the cam from the start then straight up should work fine. Good luck, these kind of things make a gear head go bald!
 

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When we advance the timing it will diesel really bad. If the timing is retarded a bit it wont stay running. The cooling system is circulating for sure so i dont believe we have any air pockets. we only have at most a 9.5:1 compression and are forced to run 91 octane and octane booster if its ran on the highway. Im wondering if going to an inline electric pump would be a better idea to use instead of the mechanical for the carburetor though its only a 650 edelbrock. Could advancing the cam shaft help as we just installed it to the center line? I have wondered for a while if a bad fuel to air mixture could cause such a drastic change in temperature or not.
Dieseling has nothing to do with the timing since it diesels without any ignition (spark). Dieseling is caused by fuel and air allowed to flow into a hot engine and ignition from existing heat and compression. I suggest an anti-dieseling solenoid on the carburetor that will shut the throttle blades completely when the ignition is turned off. Once the dieseling is stopped, adjust your timing to say 10* initial and around 40* total, make sure the vacuum advance is working properly.
Is your radiator cap holding pressure? Are you losing coolant? Is the radiator boiling over?
351C head gaskets are marked FRONT. If installed backwards the engine will indeed overheat.
Some engines naturally run warmer than others. I had a 67 Fairlane GT that would run 230+ in traffic with everything right. I finally installed an 18# radiator cap and forgot about it, drove the car as a daily driver for two years.
 

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It's also possible that, if you didn't have the bores sonic checked before overboring, that your cylinder walls are too thin in spots. My original C from my Cougar was overbored .030 and instantly went up about 30F in operating temp because of this. Thinwall casting tech was fairly new to Ford and the C can have porosity and too-thin areas because of this. This is why you have the bores checked before you overbore any Cleveland. Some standard blocks that are worn need to be sleeved and then bored, though this is quite rare.
I've bought and tossed 10 Cleveland blocks so far because of thin walls and porosity.
Art's suggestion about the head gaskets is probably the better one. It's easy to get them backward if you don't pay attention, what with the bore spacing and all that.

I've also seen rebuilt engines with freeze plugs inside them where the n00b at the machine shop tried driving them out with a screwdriver but instead pushed them into the water jackets and left it/them there and just put new plugs in. The old ones float around til they create a blockage.

Otherwise, all good suggestions above ^
 

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Did you remove the fan shroud or go to different spark plugs? Do you have a 351C thermostat and not a 351W installed, they are different.
 

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As others have said, head gaskets are directional, and will cause it to overheat and there will be no cure for it. Also, the block must have either the brass restrictor in it with a Cleveland specific thermostat, or a blocked restrictor with a windsor thermostat. I have a 180° thermostat in it, but it runs consistantly at 195°.
 

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Discussion Starter #10
Thank you all I will check the head gaskets and the thermostat just in case. I was thinking for the most part that the bore played a large roll in the heat being excessive. The block was fully inspected by a guy that has been building and machining engine for about oh 60 + years. His dad did the same. I really appreciate the posts and help. This problem has been a pain as we have spent hundreds of dollars in water pumps, radiator and cap, fans you name it ive done it. Now its time to take the motor back apart I guess or at least the heads. Im almost ready to just upgrade (I wish anyways). THANKS again and if you can think of any other C special parts in that area I would really appreciate it.
 

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I had the same problems with my 70´351-4v cleveland. What I found out is that the water does circulate but only in the front of the engine, it does not go in to the block because of an air pocket. I also used to many $ on things that I did not need after all. New, radiator, several thermostat, water pump, change the head gasket two times, and so on, and so on....
 

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Have you tried this?

<table id="Contents Table" width="600" border="0" cellpadding="0" cellspacing="0"><tbody><tr valign="top"><td width="600">
</td></tr><tr><td>
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</td></tr><tr valign="top"><td width="600">1970 - 1973 Mercury Cougar / Ford Mustang 351C Water Restrictor Plate - Repro
(Click Here for More Information or to Order)

Part #: 10003234
Price:$17.85


It has been an accepted fact for decades now that the 351 Cleveland bypass system was not the greatest idea Ford ever came up with. The unique 351c thermostat "hat" never seals well, causing a certain portion of coolant to...

</td></tr><tr><td>
</td></tr></tbody></table>
 

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Is it boiling the coolant and spewing it out or just running hot on the gauge?

Have you tried another gauge sender?

Best way to keep a Cleveland cool is to make sure you have restrictor in place ( which you said is there) , using a Cleveland thermostat (160 or 180 work fine - the generic cheap product available in the US is for a Windsor), get rid of the fan clutch and run a spacer that puts the fan close to the radiator, use a 17" rigid 6 blade fan designed for air con cars, make sure you have a shroud

There are some hi-flow thermostats available for Clevelands

http://www.grandtourer.com.au/Aspx/ProductDetail.aspx?ProductID=1491&4=ypPZer9ltHEI+XurGWbhlpeAKgq5eyzUHEs6K5usDjp5xqLMee1RINVvDhZDc3CZozntLMk6uMxMzXTU+JFbtu0H6fpoIu72qS833qfRzyU=

http://www.fomoco.com.au/Shop/Parts/FANAC.gif

Go here and search for fan and thermostat for some of the items. These guys specialise in Clevelands - http://www.fomoco.com.au/Shop/
 

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my 351 Cleveland runs pretty consistent at 195F. Is this normal operating temperature? I am new to driving this car, as I only drive it to shows, so while I understand it won't run like a modern car, i also want to be comfortable in knowing I won't lock the engine due to overheating. It only really gets hot after I shut the engine off, and the coolant stops circulating. I figure this is normal. Speaking of normal, why on earth was the car designed without a coolant return or overflow installed??? I have the proper amount of coolant in the radiator, but when I shut it off, after expansion, all the excess coolant sprays all over the ground, and I have to refill it again. What the deuce?
 

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If it holds at 195 it is probably the operating temperature for the engine. Mine runs around 190 - 195 and up to 200 on hot days but it doesn't overheat

If your radiator isn't overfilled then blowing coolant out after you turn it off could be a symptom of a stuck or partially opening thermostat
 

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Be sure to pressure test the entire system -- any lack of pressurization will cause the temps to increase. Usually a free tool rental at the local autoparts store
 
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