There are other fans out there but if you have a 7 blade fan already I would start somewhere else.
There are several different stock pulley arrangements out there depending on whether the car was an AC car or not, certain years, etc. It might actually be worth measuring the pulleys to make sure you don't have a mismatched set that's underdriving the fan and water pump. The other thing is there was a HV and standard pump from the factory, so it's possible you have a mismatch there, ie, an HV pump pulley set with a standard pump. I kinda doubt it since airflow seems to be the issue but it's possible.
Here's a list of cooling specs. If you already have a 18" 7 blade fan, then I would measure those crank and water pump pulleys to determine the ratio. If you're underdriving the fan it would hurt you at idle.
This is hard to read because of it's size, but if you go to
MyMopar - Mopar Forums & Information - Service Manuals and download the 1970 Plymouth service manual and go to page 228 you can see a full size version. If you have a .95:1 ratio you should have an 8 blade water pump (HV), if you have an A/C car with a 1.4:1 pulley ratio you should have a 6 blade pump.
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Fixing the shroud will also help, a little bit of efficiency can make a big difference. And you should still check to make sure your fan clutch is working properly. If it isn't, your fan may be spinning slower than intended at idle.
Guys, if the only reason his temp didn't climb
above 215 is that he started moving again, he might have a problem. If it climbed to 215 in traffic and stopped that's fine, but that's not what he said.
There is no reason to cut the radiator support for the 26" radiator if it currently has an opening for a 22" radiator. For several reasons.
First, the car runs fine at speed which is when the opening in the radiator support would be restricting airflow. The car is heating up at idle, when the fan is moving all the air and the fan shroud means that air is in fact being pulled across the entire radiator core. So, the heating issue is when the entire core is having air pulled across it by the fan and the radiator support opening has no effect.
Second, even with a 26" radiator behind the opening for a 22" radiator, only a small portion of the core is covered by the radiator support. Like less than an inch per side, it's not a 22" opening. And the support isn't directly against the 26" radiator core. Which means even those outside tubes are exposed to plenty of airflow.
The advantage of the 26" radiator is additional surface area and volume. You still get both of those benefits even with the support for the 22" radiator. The 26" is still giving you better cooling than a 22".
I've run the 26" radiator in my Duster behind the stock radiator support for a 22" radiator for the entire time I've had it. It's never caused an issue for me. At speed the car has never had an issue with overheating, and at idle my fan shroud covers the entire radiator, pulling air across the whole core. There's no need to cut anything under those conditions.
