First I need to humbly apologize,
I have been using and telling people to use the typical thermostat.
I am wrong...

Sometimes, even if your a professional and supposedly the "guru" of an engine, you can be wrong.
Since we build and dyno engines, we don't see the real world driving conditions.
That is why we have used the typical stat, on the dyno, it doesn't bother it.
I visited the local Carquest today, had them grab me a stat for a 79 f-150 with a 400. Then he looked up for a Mustang with a 351C...same stat.

Reason we got into this more seriously, is with machining the new Track Boss Cleveland block, we are studying the cooling system.

Our game plan is to make the brass restrictors for the Cleveland block to a customer can use the convential stat and we will make it so the customer can use the stat with the "Hat"
We also plan on making the hat so it can be added onto the performance type stats like Robert Shaw.

So I feel %100 that the 351C/351M/400 CAN use the same stat W/ the hat design.
I do feel that the hat style is the best choice, even though I have seen the other used without issue.

 

I have a long history of 35m/400 engines. I have never seen one with a thermo that has a foot on it. I have never encountered one as a replacement. I know this comes up a lot but maybe the foot style is for351c.

http://www.fordparts.com/Commerce/Pa...rd&model=F-100

 

Tim - I think we are on the same page. I've done a lot of reading on this topic recently, and I put together what I've learned about it here: 351M/400 Thermostats - ???Gary's Garagemahal. Please take a look and see what you think.

Now for where we may differ. You said your official response is that you are neutral. But, as shown on my page, Ford specified the RT-139 thermostat for 351M/400 engines, and that 'stat has the hat. Further, I believe running a "hatless" thermostat in a 335 Series engine will reduce cooling efficiency significantly - over 10%.

So, why do that? Bottom-bypass or hat-style thermostats are readily available and for little if any more than a hatless version. Therefore, why not run the correct thermostat for the engine and get the added efficiency? Or, said differently, why be neutral? Why not tell people that Ford designed the engine to use a hat-style thermostat and that's what should be used?

 

I often wondered why my truck, with a 351c, would take a lot longer than my girlfriend's car to get to operating temperature.

Turns out I had a Windsor t/stat installed.

The local shop that imports and sells our truck parts did not know there was a difference, and neither did I.

I read an article, here in FTE I think, back in 2013, which illustrated the differences.

As soon as I fitted the correct t/stat, operating temp was achieved quickly, just like a modern car.

Hope this helps.

 

Hopefully this attachment opens properly.

 

That one does, but the other two are bad. Ugly!

On the PDF, is that from some web site? I might want to use it on mine.

 

Hi Gary,

LOL, ugly is an understatement !

I tried to delete them but couldn't.

To be honest with you, I have no idea where I got the info from.

I wouldn't be surprised if it was from an FTE thread though.

Your 10% efficiency comments make sense by the way.

 

Thanks. The 10% is based on area. I calculated the area of the bypass passage vs that of the passage to the radiator, and found it to be 12%. However, the bypass passage has a straight shot where the one to the radiator has to make a sharp turn, so I'd bet the flow rate is higher than 12%.

 

Well like Tim said, don't get to smug to learn something new. I will see if I can try one with the hat if I can find it and report back on the warm up period.

It is odd that the link to FORDPARTS.com doesn't seem to show a hat.

I thought the restrictor in the 351C was to slow down the flow so it had time to pick up the heat. Maybe not.

 

The thermostat in the link is an RT-1139, not the 139 that the catalog calls for. I think that is an error.

 

Gary...We are %100 on the same page.
So here is what I did.
Been looking at the "M" block and the "C" block to compare the water outlet area. Thinking I can change the design of our block for easier stat availability.
That is another story...
But what I did see is that both block are identical except the restrictor area.
But the bottom line is they both had the same .750" size.
And Gary outlined that on his web page.
Then I stopped at a couple more parts store and had them pull me a stat for a '79 400 engine. All 3 had the same stat with the "hat" on it.
So, that is why I had made the comment about a hat type stat can work in a "M" block, and I would suggest it also.
Reason why I stated I was neutral is as "beartracks" said, I have seen the non-hat stat used without and issue. And as we tear apart engines here, I have not seen one come out either. But the originally installed stat will probably not be in a 40 year old engine anyway.

I am going to make a change to my original post.

 

Tim - We are in agreement. I believe the cat in the hat is the best approach. And I believe the reason you don't see problems is because most cooling systems will handle the 10+% bypass. But why chance it when the proper 'stat is available? Not me - especially in my Tim Meyer-built torque monster.

 

OK, as I think I understand it.

The hat style will help with cooling but not with warm up time.

The restricter used in 351C will not affect cooling but I guess it provides a seat for the thermo foot.

My problem at the moment is actually too much cooling. I have a big aluminum radiator and a 180 thermo and two electric fans. The fans hardly ever come on anymore until I drive extensively (summer). I run a 192 in winter I used to have cooling problems with a smaller radiator. I wish there were a 185 thermo. I'd run it year round.

Oh yeah. 435hp and 510fp on paper.

Teacher, can I be excused? My head is full.

 

While your understanding about warm up time fits with mine, it doesn't fit with FMJ's experience. And, while I cannot explain it, I'll defer to experience.

However, I do agree on the cooling. Class dismissed.

 

I have had countless of these engines, seen many that overheated. Fixed about 4 of my own overheating issues by installjng the napa t stat with the hat. I have also seen a couple of these engines burnt up, very evidently overheated, and the t stat removed was wrong. Now, that doesn't mean that the overheating would have stopped due to right t stat, but allin all, the cooling system was made less efficient. Thanks and I appreciate the posts. They help us 400 fans.