using 50/50, going to stat back in see what that dose just went around the block,parked it and it started blowing out the over flow. I was told the cleavland is the same as the 351m and the 400,I used cleavland head gaket could that be a problem. package said 351m 351c & 400. but could the water passages be to small. is there a difference between 2v and 4v heads that could cause this problem.I know my heads are 2v

 

I just rebuilt my 400 M-block last summer; yes, from this standpoint, the 351C, 351M &
400 are the same. These engines don't have a coolant cross flow via the intake manifold;
rather, there's an exhaust cross flow there. As was said earlier, it is VERY important to
make sure the head gaskets are installed correctly when assembling the engine,
installing them backwards will cause problems like this.

You might look up/acquire this book and find where the author talks about it:

Amazon.com: Rebuild Ford V-8 Hp36: Tom Monroe: Books

You might also post your question in the 335 forum, plenty of M-block experts there:

https://www.ford-trucks.com/forums/forum54/

You're right, there was no serpentine belt system for these engines, at least none that
I've ever heard of or come across.

These engines *do* heat up fast; 5-10 min is all that's required to get up to a decent
operating temperature (160 or so).

This reminds me; have you put a known-good water temperature gauge on it? Factory
gauges are known to be, um, less than reliable sometimes.

Regardless, reading through everything here, it sounds to me like there are 2
possibilities:

1. Coolant flow is blocked somewhere;
2. There is air trapped in the system.

If you're gonna install a thermostat again (make sure you use the correct one, this one
is unique) then I'd suggest flushing the system through a T installed in a heater hose at
the same time to forcefully remove any trapped air and see if your problem persists.
And, check the archives of or ask on the 335 forum.

Good luck.

-chris

 

I think I paniced I let the motor run 20 or 30 min after putting the thermostat in (all the parts store had was 195 degree) have an after market guage placed same spot as stock sending unit. never got over 195 let it purge kept the radiator full of water. got to 205 after I shut off engine but I think that is normal. it didnt blow out over flow this time.thats the good new,while doing this found out the altenator is bad .just my luck lol thanks for all the input it really helped

 

Aftermarket places will give you 195 thermostats, I understand Ford specs are
for 192 (making 195 close enough).

 

good too hear it worked out for ya.

 

Another thing: If your head gaskets are on wrong, the block will more than likely
think everything is fine but your heads will melt. The gaskets have FRONT
stamped into them at the top (where the square hole is located).

 

I agree. What you can do first is take a sensor or a plug out of one of the water ports in the intake, and make sure water is flowing out. This will let some of the air out, but there still may be some trapped in the engine, so run it with the radiator cap off, and let it burp out. It will burp out, and the drop back, and then burp out and overflow again, and it may do this two or three times. Then it will seem like there is no water in the radiator. But keep an eye on it, and when the top radiator hose starts getting hot, you know you have all the air out and you can go ahead and top it off.

 

ok thanks will try that

 

cant find a water outlet in the intake pulled intake off no water only two exhust flows one in the middle undr carb, one in the very front. Im running an elderbrock performer400intake with a 600 cfm elderbrock carb.dose this mean a hed gasket is in wrong?

 

As I said earlier, the M-blocks don't have water flowing through the intake manifold, they
have an exhaust crossover there, instead. Head gaskets installed wrong will keep water
from flowing through the heads.

One of the best online resources I've found for the M-blocks is Bubba's M-Block Workshop.
Unfortunately, that site seemed to have disappeared in late 2007 but there's an archive of it
available here:

M-Block 351M/400 Parts Reference

What Franklin suggested seems like a good idea, you might disconnect the heater hose
connection from the top of the block instead of from the non-existent intake manifold
connection.

If it were my engine, I'd let it run until it got to full operating temperature (until the
thermostat fully opens) and then flush water into it through a T in a heater hose, letting
it exit from the top of the radiator; this should flush out all trapped air. If the problem
persists, there's something bigger wrong someplace....

 

i pulled a head off, I screwed up one of the passages was blocked. getting some new head gaskets and starting over. that should fix the problem I hope.I will never build another m engine.looks like Ill change to a windsor when this motor goes bad thanks to everyone for all the help

 

Sorry about the miss-info on the sensor thing. I forgot the M has a dry manifold, but the other suggestion about the heater hose will work, although don't go twisting and jerking on the firewall heater hose connection, or you can cause the heater core to leak.

After you fix the head gaskets, and are filling the engine back up with coolant, leave the highest heater hose connection on the engine off and keep filling till coolant starts flowing out, and quickly put the heater hose back on. You are still going to have to burp the engine when you get it going.

 

next step, i think this modified motor would make a great boat anchor