My Big Block does not like traffic on hot days. Runs cool at city or highway speeds. 26 inch 3 row alum rad..6 blade steel fan..shroud(blades half in/half out) stock waterpump 180 degree milodin thermostat. Now it appears to me that it is not getting enough air flow through the rad at idle or the waterpump could be upgraded to a high flow. It's a 67 dodge and there is not enough room for stock fan and electric fan.

so is the answer an electric fan system that can push air at the equivolent of 30 to 40 mph , what would be the cfm, or try the HV waterpump? Thanks in advance to all.

Is it possible that your pulleys are wrong? Might be turning the fan too slow.

Stock pulleys

recently switched my 440 over from an electric water pump (w/o a t’stat) to a FlowKooler water pump and 160F t’stat. I noticed about a 20 drop in temperature. It will idle at 185 for over 30 minutes without moving the gauge.

I am running a 26” 3 core as well but I do have dual electric fans. In my opinion, the water pump swap may be the low hanging fruit - cheapest and quickest install vs throwing an electric fan on it. Just my 2 cents.

There are all kinds of “stock” pulleys.

What is the diameter of the bottom one versus the top?

My 1st question would be....how warm does it get? What is being used for a gauge?

Also,
What are the core dimension's H & W?
How big is the fan?
What is the distance between the shroud opening and tips of the fan blade?
When the engine is idling will it hold a shop or paper towel to the front of the radiator?
Will it do so across all areas of the radiator?
I would start with the above

Lastly, putting a fan in front of the radiator is not recommended as it can block the air flow at higher speeds

With electric fans, one normally gets what they pay for and CFM ratings are typically skewed especially on the cheap ones.
There are a number of sources depending on the room available.
Also, the higher CFM fans will draw more current so the charging system and wiring HAVE to be in good shape and sized appropriately

7 inch top...6.5 bottom

3 row 26 inch rad

blades are half in shroud ..half out.. at idle sucks a paper towel instantly and holds it there

Your pump is under driven then with those dimensions.

Putting a larger lower pulley or smaller upper will increase water flow.
That may be all you need.

I wen tot Bouchillion's website to see how the numbers compared. Not sure they are measure the same way the OP is.

In regards to the pulleys?

3 questions Not answered

What are the core dimension's H & W?
How big is the fan?
What is the distance between the shroud opening and tips of the fan blade?

And a few more:
Does the paper towel suck up to the radiator evenly across the entire core?
Will i t do the same with a shop towel ( heavier)
Is the Shroud sealed to the radiator all the way around?
You might try taking some temp readings at various areas of the core as you may have uneven cooling for a number of reasons.

Yes, they sell various pulleys so i went there to see if their dimensions matched the OP's, not that I could tell.

What about timing?

Is the engine over bored a lot?


One thing I learned after years of dealing with this stuff and reading on here, shrouds and fans aren’t that big of a deal. If you get some important stuff correct that is. You need a good condition radiator and you need a good pump. Pulleys are worth looking into, I don’t have a magic bullet set of numbers to post. Just do some research and ensure you have something that will work.

I had a 69 rr that by happen chance came with a broken shroud somebody had duct taped. That just fell on apart one day and I planned to replace it soon. Then I noticed it didn’t make a difference, so that car never got a shroud. People used to freak out about it because the gospel is you must have one. I even started running a 195 factory stat because I didn’t care for the oil turning black so quickly, that made no difference on an auto meter mechanical gauge as far as getting hot. Sat right in the stat all the time. Idle, beating on it.

Also learned on that car that you don’t have to cut the 22” core support when running a 26. Guys freak out about that.

One day I was showing the car to a family member and he said the fan was on backwards. It came that way and I never noticed or need to check as the car never ran hot. I flipped it around and it made no difference. Not even a little.

The recipe?

Stock factory built 383 hp that I poured the sand out of on the stand when I did a little going over and a new chain.
Stock 26” radiator in a 22 hole
Edelbrock pump
Some random aluminum housing. No idea on who made it.
March serpentine belt pulley set that didn’t serpentine, just ran the belt in stock pattern
Stock fan and fan clutch that was good
Good sharp tune up
Jet hot coated headers
Ran right on a 180 and a 195 stat on mechanical gauge even on 90+ humid days

stock bore..molnar stroker crank....timing is fine

Lot of unknowns. You can flush the motor and radiator, see if that helps improve cooling. The Chapter 7 of SM has the cooling specs on pulley ratio, water pump impeller, fan blades. Lot of different stock components.

motor and rad is fairly new and the issue has been from the beginning.( it doesn't streak to a higher temp in traffic..it takes a while to get to 200 . I have tried most everything except going to a HV pump vs stock and upgrading to a 4 row aluminum. I'm not enthused about electric fans but as stated in My original post the car runs cool down the road even on the hottest days so at idle it is not getting enough air through the rad or the circulation may be too slow. With the setup as is...IF the fan could pull air through the rad at the equivolent of 35 mph...it would never go over 180. Down the highway on 90 plus days the car runs at about 175-180.

Do you have an auto trans routed through an internal cooler, do you have a a supplemental cooler in series and where is it located.
I'd try a new thermostat that is tested fir
The pulley situation should be sorted out first.
Flow is important, yet flow can be too fast to effectively cool the water properly.
Is the shroud from the 22" or 24"?
Check the auto trans pan temp for trans temp, and or make sure sender is on correct bung or line (hot area not return) to verify that.

Is the fan direct drive or are you using a fan clutch? Maybe some pics of your setup could help.

So....how hot does it get?? Nothing wrong with 200F