Odd Overheating Problem

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I wanted my 440 engine to run a a little warmer. It had a 160 degree high flow thermostat and so changed it to a 195 Stant Superstat. 15 minutes of warming up and then started cruising at about 35 mph. As soon as I stomped on it the temperature gauge began to spike and I saw steam starting to come out from under the hood. So I quickly pulled over. The coolant was not steaming from the radiator - it was blasting out the stat housing gasket area. The radiator was barely warm - I could rest my hand on it. So I thought it was a stuck thermostat. (Yes, I did install the stat in the correct direction.) I then bought a new Milodon 180 degree high flow stat. Boiled it and it opened right at 180, give or take a degree. Installed that. Drove around all day around town and on country roads, and a short highway cruise of about 70 mph. Thought I had it fixed. Then, right at the end of my cruise, I decided to stomp on it from about 15 mph and took it up to 75 mph. Here we go again. The temp spiked, I saw the steam, pulled over, coolant blasting through the stat housing gasket again. The radiator was hot this time, but not as if it was overheated - no steam coming out from it.

I know you might be thinking, just put the 160 back in. The problem is the engine always ran too rough, especially on 50 - 60 degree days, as if it never got warm. It ran tremendously better with that 180 stat, but now I have this overheating problem.

Never had an overheating problem and the engine has barely 2500 miles on it. Griffin aluminum radiator, aluminum hv water pump, shrouded, 7 blade fan, no AC, etc. I didn't make any other changes, just the stat. Any ideas?

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Would a defective radiator cap cause this?

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Yes, you may have a pressure leak, but on a big block dodge, if it were at the thermostat housing you would most likely actually see coolant escaping the sealing surfaces.
Now for the people who were telling the poster to drill another hole in the thermostat housing, or insisted he had a bad headgasket, you're all idiots.

The air pocket thing is the correct answer, but not to be addressed in any way you guys were thinking.
Any time you drain the cooling system of any coolant (especially if you drain enough to clear the thermostat on a B/RB motor), the air must be burped out of the system after refill while running.
There was a thread on this on here a year or so back, where there must have been 100 replies from people with nonproductive, or mildly destructive theroies on how to get air out of a cooling system. And when myself and one other person chimed in with the RIGHT, EASY, and CHEAP, and PROFESSIONAL way we were shot down and disregarded as fools.

I am a mechanic for a living and have been for many years, and this is what ALL of us use, and its the ONLY way to fly https://www.matcotools.com/Catalog/toolcatalog.jsp?cattype=T&cat=2125&page=15&#62923
Matco tools Part #SFF2A Cooling system burper kit. $30.
You seal the funnel on to the top of the radiator and fill the system through it. Then, when it takes all it is going to take, fill the funnel halfway full and leave its plug out. Fire up the engine, and the system will likely start drawing coolant from the funnel. keep it half full the whole time as you can, and as the engine comes up to temperature the pressure in the system will drive the funnel to a more than half full. (this is why you never have it more than half full when cold, so as to prevent spills) when the thermostat finally opens, you will have tons of air coming out of the system up into the coolant filled funnel, and getting replaced by coolant from said funnel. Turn the heater on full temp once the thermostat opens too, to get ALL of the air out of the cooling system. This will remove all of the air from the system that there will be, and run the engine and dont be afraid to rev on it a bit to get the water pump pumpin away after the thermostat has opened to knock all remaining air out.
Right before you shut the engine down FIRMLY place the plug in the funnel, to keep in the built up cooling system pressure (this is very important) and then walk away and do not touch that plug until the upper radiator hose has collapsed on itself some (indicating the pressure has reduce, and the now sealed system is sucking back on itself). Then remove the plug, and it will draw in even more coolant, and give each radiator hose a squeeze or two to knock any air sitting in the upper hose or upper core of radiator out. Replug the funnel, then remove it from teh radiator, and reinstall the cap.

It's not rocket science, and I don't care what your daddy or neigbor or whoever told you, but just filling the radiator and letting it run, and then topping it off sometime later leaves a good 75% of the displaced air in the cooling system in there. And with the air in there, you might as well have a pressure leak, because the thermostat does not open and flow for air. It does for coolant.
Plus, chrylser B/RB engines have internal self bypassing cooling systems, so the coolant that is actually flowing without the thermostat being open is also not going right by the thermostat (like an amc V8 or dodge LA motor does).

This concludes your lesson for today kids.

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GreenBlurr, you may have a good point but people are not going to bother listening to it if you need to degrade others just to try and get your opinion across. Talking down to someone will just turn them off to you.

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GreenBlurr,

I to am offended at your response. Frankly we can do without your comments. To assume we are all idots and kids is foolish. If you want to comment on a thread keep it civil or keep quiet.I would have thought maybe you had a bad day or something but since you commented twice I believe you are just that way.

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To some people thier way is the only way. The rest of us don't know anything.
Yeah those 'tools' do work but there are millions of cooling systems filled without using this that that have no problems. Evidently this is just idiot's luck.

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GreenBlurr,

I to am offended at your response. Frankly we can do without your comments. To assume we are all idots and kids is foolish. If you want to comment on a thread keep it civil or keep quiet.I would have thought maybe you had a bad day or something but since you commented twice I believe you are just that way.

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To some people thier way is the only way. The rest of us don't know anything.
Yeah those 'tools' do work but there are millions of cooling systems filled without using this that that have no problems. Evidently this is just idiot's luck.

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Yea that was harsh, I know you get aggravated by some peoples response when you try to help but you should blow it off.

I guess I have been lucky over the years. Last weekend I flushed my 71 440s coolant and let run for about 20 mins in the driveway and all seems well?

"Got everyone's attention though didnt i. and now they read, and now they learned."

I learned not to talk down to people, thanks.

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Where do I pickup my prize?

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Right here Just because his stat housing doesn't leak anymore, doesn't mean his problem is gone. Appears as though his over-heat problem went away with the new stat housing also?????????? Normally, the highest cooling system pressure occurs after shut down, when the engine heat soaks ( and that's when the stat housing leaks at it's worst), not as you rev up the motor - unless you are pumping air in to the cooling system. Not sure who anymore, but someone used to sell a kit that would detect exhaust gasses in the cooling system. Good way to verify that all is ok.

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He didn't have a overheating problem before he changed the thermostat, why would have one after changing it other than the thermostat housing leaking???

What do you think he should do? Change the head gaskets??

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Where do I pickup my prize?

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Right here Just because his stat housing doesn't leak anymore, doesn't mean his problem is gone. Appears as though his over-heat problem went away with the new stat housing also?????????? Normally, the highest cooling system pressure occurs after shut down, when the engine heat soaks ( and that's when the stat housing leaks at it's worst), not as you rev up the motor - unless you are pumping air in to the cooling system. Not sure who anymore, but someone used to sell a kit that would detect exhaust gasses in the cooling system. Good way to verify that all is ok.

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He didn't have a overheating problem before he changed the thermostat, why would have one after changing it other than the thermostat housing leaking???

What do you think he should do? Change the head gaskets??

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Read his entire post - including the post title ( "odd overheating problem "). Leaky t-stat housings don't cause overheats, but overheats can cause leaky t-stat housings. I think he should go a little farther to verify he doesn't have a head gasket problem - if his initial post and diagnosis as an overheating problem ( only when he mashed on the gas pedal )was correct. Obviously, time will tell. Here is your prize =