Hello I have a Question and open to suggestions.
I have a 1968 slant 225 in a GMC that is overheating (210-220 degrees)
It has an aluminum radaitor with 2 one inch rows
13lbs cap
50/50 coolant
rebuilt water pump (possible cause?)
A/C installed
I live in S Texas where summer temps in 107-112 degrees are normal
Is there an aftermarket water pump available?
It runs hot driving down the highway so air movement not the cause
I have a 180 thermostat.

Start with the simple stuff: Have you verified actual overheating, or are we dealing only with an indication (on the gauge) of overheating? Are you sure the cooling fan is installed right way round? Did you pan-test your thermostat to make sure it actually opens at 180°, and are you sure it's installed right way round?

That 2x1" aluminum unit should be more than plenty of radiator if it's in good condition. Water pump is probably not the problem. What's the history on this block — was it totally taken down, cleaned out and rebuilt? Or is it a drop-in with unknown levels of crud in the water passages?

Other factors that can cause overheating include exhaust restriction, improper cam timing, and improper ignition timing.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

The engine was purchased from a gentlman who installed a v8 in a dart and had records of the previous owner. The engine was maintained at a dealer and showed 47,000 miles up to the point of sale.
I need to pan check the thermostsat
The overheat seems to happen around 108 degrees, at night around 90 degrees the engine runs at 190
The fan is working since tissue paper gets pulled into radiator on opposite side.

What purpose is the exhaust valve under the carb? It moves freely is it possible to remove it since I think its purpose is to vaporize the gas going into engine.

Don't get sidetracked by the manifold heat control valve; it is not causing your engine to overheat, and removing or otherwise tampering with it is not going to get you anywhere you want to go.

Old low-miles engines often contain a great deal of gunk in the coolant passages. The block can be cleaned out by removing the rearmost freeze plug and the lower radiator hose, and scraping/flushing forward from there. If you find a great deal of mud, you may need to remove additional freeze plugs.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Interesting truck - got more photos?

Is the overheating a recent development?
What shape are your hoses in? Any chance a hose is collapsing?
At what speeds does the overheat occur?
Do you normally drive with the hood on?

Airflow can be a funny thing. Even a radiator stuck out in the breeze might not get the flow through you'd think it would. You might try some ducting to make certain the air coming in the grill is getting through the radiator.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

It seems to happen anytime the outside temps reach 100 and over.

I'm just guessing here but with the hood off and that big grill I'll bet the air is going right over the top of that radiator and its not getting a good flow thru. Maybe a fan shroud would help suck more air thru? I would also follow Dans suggestion and clean out the block, it may not have a lot of miles but it still has a lot of years on it for gunk to build up. Looks cool though.

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Grandpa's 1974 Dart Custom 4 door 225 auto, Aluminum Radiator, 1920 Holley.

Is there a smaller diameter water pump pulley available to spin the pump faster, I have a small block chevy pulley that seems smaller but the groooves dont match perfectly. I will try it to see what results. The thermoststat opens at 180 according to the gage(my hand on the hose). The water coolant is clear(after draining). I will also check timing.

No, and you don't need to spin the water pump faster. It's spinning plenty fast enough with the stock pulley. You need to determine if there's actually a real overheating problem, and if so, you need to find it and fix it. Re-engineering the engine's cooling system will not be required.
While you're at it, check the other factors that have been suggested to you. Airflow thru (not over/around) the radiator, exhaust restriction, cam timing, etc.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Engine gods...I need help...

I still run hot. 200deg with a 160deg thermostat(100 deg day..3200rpm@70 mpg...ildes at 160 all day long with ac on)
I have tried 190, 210, no thermostat.
I installed a 2700cfm electric fan from a Mustang.
I had a valve job done and replaced the head gasket(installed hardened seats)
Removed the freeze plugs and cleaned the inside of the block.
Adjusted timing up and down.
Installed a hood
Repaced the aluminum radiator with a 3 row jeep wrangler radiator.

I notice suds or foaming of water when reving the engine to 3,000 rpm then return to normal when idling.
When I rev and notice the suds, the temp starts to go up
My question is this...is the slant six made to operate at this rpm for long periods of time?

I installed a backing plate to the water pump blades thinking water cavitation was causing the suds, but it continues.

I thought that an engine could be overcooled but this one wont.

Im at the end of my wits!!

The water pump backing plate is interesting, but you've got a problem with your engine that needs to be addressed by diagnosis and repair, not a system inadequacy that needs to be "fixed" with upgraded components. Foaming makes me wonder about a head gasket leak. Time to use a Blok-Chek or other method to determine if there's exhaust in the cooling system.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I second that.....your not suppose to see any foaming like that. Air is getting introduced into the system. Hopefully not a head gasket leak.....but it maybe the culprit.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Head gasket was repaced, along with a vave job, resurfaced head, two worn valves and hardened seats.

Welp, you've got two choices here:

1. Do some proper systematic diagnosis, find the problem, and fix it, or

2. Continue insisting it couldn't possibly be something the matter with the engine and carry on wasting money, time and effort on more thermostats, radiators, fans, water pump modifications, and bizarre questions about whether the slant-6 was meant to be run for extended periods of time.

You've received sound advice. I really don't see how we can help you further. It's time for you to help yourself.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.