getting hot at stop lights and when shut off

1973stang · Jul 11, 2010

Okay so heres the situation, Ive got a rebuilt 351C .30 overbore. That is getting hot at idle after being ran for awhile or after it is shut off. I replaced the thermostat 180 fail safe, cap, hoses, and even have water wetter in with the 50/50 mix. It doesnt have a fan shroud which I plan to fix but that wouldnt solve the problem after its shut off. Any thoughts? Is it possible my radiator in my 73 isnt enough? Should I go with an aluminum one? why does it primarily get hot after I shut it off, I mean I know its a lack of air flowing and the waterpump not flowing after its shut down... any suggestions or input would be great.

rbohm · Jul 11, 2010

the lack of a fan shroud is part of the problem as it allows air to recirculate around the fan tips. as for it boiling over after shut down, part of that will come from running too hot at idle, and part from heat soak. remember that the 351c block is a thin wall construction, and you have bored it .030 over which means more heat is getting to the cooling system. also your radiator, did you have it cleaned out before reusing it? if not that will also be part of your problem. you dont necessarily need an aluminum radiator, but you do need one that works properly. a good three core copper/brass radiator, or a good two core aluminum radiator with 1" to 1.25" tubes will do nicely.

1973stang · Jul 12, 2010

I did have the radiator cleaned and will probably give a jegs/summit 2 core aluminum a chance, do you think between that and the fan shroud I could be looking at a solution to this?

other_shoe · Jul 12, 2010

Also, check out this thread

http://www.stangnet.com/mustang-forums/817689-67-mustang-radiator.html

Apparently, there is a special thermostat and set up for the 351C. You probably know that already, but it could be important if you did not.

tlindsey18 · Jul 12, 2010

Like he said, first make sure you are using the correct thermostat for a 351c, it will make a HUGE difference. I just went through the same issue with my 351c, I had my stock (copper/brass) 3 core for a 67 coupe rodded and he told me it was 30% clogged....now it runs around 190 all day long in any situation. I also installed a 14" electric fan, but it was running fine before that.

RogerC62 · Jul 13, 2010

The correct thermostat has a bowl on the bottom that works with that restrictor inside the thermostat cavity.

Hack · Jul 13, 2010

If the radiator pukes some fluid after the car is shut off, that just means that you have a little too much fluid in the radiator. It shouldn't be full to the top. This is a lesson that took me a while to learn. If you keep adding fluid it will keep puking the excess out. You have to let it cycle a few times so that it finds the correct fluid level. Then it will stop pushing some of the coolant out.

If the car actually boils over at idle, now that's a problem (if the radiator isn't over filled). It's normal for the temp gage to go up somewhat at idle, though. Does it boil over, or do you just have a temperature increase? How new is your radiator cap?

How recently was the engine rebuilt? They will run hotter until they are broken in. Are you relying on the factory gage, or do you have a good quality gage in there that reads the actual temperature? What is the actual temperature? Like I said before, as long as it isn't boiling over you are ok.

Edit: 351C should use a 190 thermostat.

1973stang · Jul 14, 2010

Found out I do have the wrong thermostat, Im hoping this makes a significant change. The car hit just over 220 after shut off and was getting around 210 at idle. I do have an aftermarket gauge. It pukes a little out but agree that could be because of too much fluid. Im still not happy with it getting that hot, and the upper hose is scalding, so it seems like this may be the answer. I will post the results in a day or two. Thanks to everyone.

tlindsey18 · Jul 14, 2010

The theromostat will definatly cause it. The wrong one will not allow it to close off the bypass (it's too short) so fluid will travel back to the radiator to cooled off!

Hack · Jul 14, 2010

210 / 220 is fine. Nothing is wrong.

Now you can spend money on the cooling system and lower those operating temperatures, definately you can do that. Just know that engine wear rate increases as the operating temperature goes down. A lot of hot rodders don't care about engine wear because engines are like candy to us - we always want a new one. However, if you're cheap like me you might want your engine to last.

I'm not going to say your engine will wear out really fast at 200 degrees, that isn't true. But if you run a 160 thermostat and keep operating temps down there, don't expect to get 100k miles out of it.

1973stang · Jul 14, 2010

Id rather run the right stat though hack, went to the parts store today, after bringing out the wrong part three times I got online and found another thread with some numbers, went back got the right one, slapped it in and now she runs great and idles around 195 after being run for quite awhile, and traffic was a breeze...

Hack · Jul 14, 2010

1973stang said:
Id rather run the right stat though hack, went to the parts store today, after bringing out the wrong part three times I got online and found another thread with some numbers, went back got the right one, slapped it in and now she runs great and idles around 195 after being run for quite awhile, and traffic was a breeze...

Yes definately run the correct thermostat!

Glad to hear it works better with the right part in there.

rbohm · Jul 14, 2010

1973stang said:
Found out I do have the wrong thermostat, Im hoping this makes a significant change. The car hit just over 220 after shut off and was getting around 210 at idle. I do have an aftermarket gauge. It pukes a little out but agree that could be because of too much fluid. Im still not happy with it getting that hot, and the upper hose is scalding, so it seems like this may be the answer. I will post the results in a day or two. Thanks to everyone.

210 isnt too high, in fact that is about where new cars run today. i do agree with getting the proper thermostat though.

1973stang · Jul 15, 2010

Just for my own curiousity, at what temp would you shut the car down in fear of harming the motor? It doesnt seem to be written in stone anywhere.

woodsnake · Jul 15, 2010

I don't think you will ever find a number written in stone for the absolute shut it off and cool it down point. Waaaay to many variables in each engine. Anything over 220 is a good point to start worrying.....

SadbutTrue · Jul 16, 2010

1973stang said:
Just for my own curiousity, at what temp would you shut the car down in fear of harming the motor? It doesnt seem to be written in stone anywhere.

220-230 is where you *start* worrying (if it hits that and you're in traffic or its 110 out, then you should stop). New cars are designed to run in that zone (for emissions purposes), but old ones weren't. 210-220 for short stints isn't a big deal though.

Getting the right thermostat will definitely help.

Hack · Jul 17, 2010

1973stang said:
Just for my own curiousity, at what temp would you shut the car down in fear of harming the motor? It doesnt seem to be written in stone anywhere.

I wouldn't worry so much about the temperature. The key is to have proper oiling and coolant flow. If it shows a high temperature but isn't boiling over and you know the water pump, etc is working and coolant level is fine - don't worry.

If the coolant boils over you should stop and let it cool right away. You should never run an engine with extremely low or no coolant, either.

Combustion temperatures are a lot higher than 200-250F! Don't worry about damaging internal engine parts due to a temperature in that area. If you want an exact temperature you need to know the composition of the coolant (pure water boils at a lower temperature than a mixture), and the pressure in the system (pressure increases the boiling temperature). As long as you have the proper liquid in the cooling system it will still function correctly and remove heat from the engine. When it vaporizes - that's when you get trouble.

Edit: one other tip is to never trust a stock or old temp gage. Trust what the engine is doing and how it's running.

pabear89 · Jul 18, 2010

1973stang said:
Found out I do have the wrong thermostat, Im hoping this makes a significant change. The car hit just over 220 after shut off and was getting around 210 at idle. I do have an aftermarket gauge. It pukes a little out but agree that could be because of too much fluid. Im still not happy with it getting that hot, and the upper hose is scalding, so it seems like this may be the answer. I will post the results in a day or two. Thanks to everyone.

You must use correct thermostat WITH the brass restrictor plate installed or you will have high temp issues.
Not having the plate below the thermostat will cause your temp problems and coolant flow issues because the coolant is not forced to go into the rad for cooling, But returned into the block.

Express · Jul 19, 2010

pabear89 said:
You must use correct thermostat WITH the brass restrictor plate installed or you will have high temp issues.
Not having the plate below the thermostat will cause your temp problems and coolant flow issues because the coolant is not forced to go into the rad for cooling, But returned into the block.

What is the part number for the correct thermostat for a 351?

I have not heard of the brass plate either, what does it look like & where do I get one?
Thanks,

pabear89 · Jul 19, 2010

Try Summit, I'm using the Flowkooler/robertshaw #333 - 180* with the 3/4 plate and it works fine.
Also search Ebay for the restrictor plate.

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