Flathead radiator cap pressure?

Start off by just retorquing your heads. Unpressurized systems I've runn find a stable level a couple of inches down from cap...anything more blows out on first run, nothing more exits.
You can test at least partially by disconnecting fanbelt from pumps and running up engine against resistance while watching water at tops of head outlets.

 

What temperature is it at when it's puking? If it's getting up near 220 then it is my contention that there is an over heating problem and a higher pressure cap won't help that.

 

Also a compression leak will add pressure within a pressurized coolant system without really getting that hot right away. Eventually yes it will get hot but pressure is also a factor here.

 

A diagnostic fot that: As trouble starts, floor it. Increased pressure from leak will show up in immediate violence, muchmuch faster than any increase in temp.
If worried, remove upper hoses (leave in original coolant, not new, as newly added will introduce extra buddles), remove pump belt, warmitup. Look for streams of bubbles, not individual bubbles wandering up to daylight. Then load engine as much as possible by revving it up a bit against slipping clutch.

 

Another look...
You may have air in your system.
remove your temp sensors from both heads. Or hoses if necessary and trickle the coolant into the system at a very slow pace.
Your baby may just need a good burping....

 

I ran a 4# cap with the stock radiator. After a couple years it started to leak so I went to a walker and a 7# cap

 

I drove a 36 Ford sedan to Memphis Tenn. in 1980 to the Street Rod
nationals. That week still holds the records around here for highest temps for that week in July. 103-105 all week. It was powered by a stock 283 with an adapter to the stock drive train. The radiator was an original and non-pressurized. It had rubber plugs clamped over the unused flathead ******s. When we got to Memphis they were evacuating older people to public buildings with AC. It was brutal. Never an over heat problem. I'll never experience anything worse than that week.

That was when the electric fans first started to hit the street rod market. We went into the vendor building just to get out of the heat. Every time I went past Walker radiator there were panicking people looking for replacement motors for their electric fan set up. That soured me on electric fans. My 4 blade belt driven fan never missed a lick.

 

This has been a very interesting thread....I'm not going to comment ,but give you guys some more food for thought....Radiator Capacity---flow rate..
I'll sit by and read some more.....while this is digested.,....

 

Yeah, I am happy this thread has turned out the way it has!! The amount of knowledge on here is amazing! I was just curious about the pressure, because of the water pumps, and what I have heard, that high pressure is no good for them.
Thanks everyone!!
Jimmy White

 

Damn I better go take my 24 lb cap that I have run for 9 years off. I have trouble getting temp in my motor can't ever seem to get it to 180 even with thermostats

 

I have a flathead with new Speedway pumps in my truck. I run a mustang radiator with a 13# cap.

It used to do the same thing, and puke all over the place real quick after driving it around. I went through all kinds of different ideas of what was going on. The radiator was full to the top, and it couldn't hold any more water.

I ended up taking one of the lower hoses off to see if there was any rust or other contaminents in it that might have stopped something up. Clean water came out, as I kind of squeezed the bottom hoses.

Just a little water came out before I put the hose back on the radiator....BUT....I was able to get a gallon and a half of water into the radiator after that! It was a big *** air bubble in the system! Everything has worked fine since then.

 

just curious where you got a 24lb cap?

 

had it left over from one of my step dad's Indy cars. It's a Stant racing cap

 

A 24lb cap is only a danger if you produce 24 psi in the tanks...if you're not running your engine at 280* it's no problem - anything beyond your temp is unnecessary.

As mentioned previously, every PSI raises boiling point (at sea level) approx 3* - so your 24lb cap is around 280-285 boiling point. Above 240, your oil goes into thermal breakdown & potentially thermal runaway, so anything much beyond a 10psi cap is probably a waste of time, IMO - I don't want my engine running at 240 (I realize oil temps won't quite be the same, but I don't want to get that close).

 

Get it sorted out Jimmy??