Look at distributor and vacuum advance.

Also...how are you running the water pump? Pulley/belt or serpentine?

Inlet and outlet check is a good idea. Not likely lean. Idle smells rich. I have a bung in the exhaust for a wide band O2 sensor but that I have not purchased yet. Will look at the Summit radiator too.

No vacuum advance. Just mechanical. Water pump is a Corvette serpentine belt pump and it is turning the right direction.

Not much truck time today. I checked timing, 12* advance at idle. 17* drop from radiator inlet to outlet. At least its doing something. Think I will check my old truck. Completely original and never gets hot.

50* drop. I just remembered something. I have a large transmission cooler in front of the radiator. It blocks a lot of air. I will do something about that in the next couple days and report back. Fingers crossed.

Is the 97 Blazer radiator you are using known to be good ? Is it possible it's partially clogged internally ? What condition are the fins ? They need to be clean and straight to allow sufficient air flow/heat transfer .

If it only overheat when idling and not when driving down the road under a load... you probably have to rethink your fan design.

I swapped out the transmission cooler last night to a smaller one. I will see how it does today.

trash the shroud and fan
 

Big pusher fans are all over the place for cheap. Shrouds are only stopping air flow. Rip out the weatherstrip under the hood to allow hot air to escape. Engine fans are limited I RPM and suck horsepower. Use coolent additive - reduce antifreeze proportions.

heat kills

Use paper to test airflow at idle.

Flow should be able to strongly hold a thick piece of paper to radiator front at idle.

Transmission cooler was a problem, for sure. Went for a drive, AC on. It is 85* F ambient here. Got back and it was 210*. I idled in the garage and it creeped up to 222* and stayed there for 10 minutes. I think I will swap the fan out for a pair of pushers. As stated above, they are all over the internet and cheap.

Thanks for all the input and ideas. I needed that.

You may have too little capacity, coolant volume. If the radiator is not large enough ( volume) your problem will likely persist. Specifically not the surface area for air flow, but fluid capacity for your combination.

Could be. I will try the fans first. I f I have to do a bigger radiator, I will need electric fans because the flex fan will not clear a bigger radiator. Unless I hack up the core support and I would rather not do that. Currently if you open the hood the V8 looks almost factory. Interior is factory down to the column shifter. Stock gauges are in place and except for one, functional.

Pretty sure someone makes a radiator for the conversion. May be pricey initially, bit it solves the actual problem. With projects like this - it's the price of admission to have the bugs worked out. Sounds simple but easily the 3 basic items. Good tires, good battery, proper cooling system - because without any 1 of those you're not going anywhere regardless if the time, effort and money spent.

I agree. I have the tires and battery and I am pretty sure fans will fix it now that the trans cooler is changed. I will do the Superior radiator if needed. For the record, I have driven it over 1000 miles without any breakdowns. But the temperature situation could just be a traffic jam away.

This.... Assuming that timing is correct and system is properly bled.

Just for fun - I checked fluid capacities for a 1994 S10 cooling system.

2.3 engine 11.5 quarts.
4.3 engine 12.1 quarts

The same year full size truck with a 5.7 is 18 quarts....

Obviously there are many factors that come into play but it's pretty obvious that the factory felt the 5.7 (350) needed a whole lot more coolant than the four cylinder or six in the S10.

angela

Angela, I am pretty sure the increased capacity in the V8 is in the engine itself. For instance the C4 Corvette radiator is the same size as the 4.3 S10. There are several ebay listings that sell the same radiator for both applications. I drove the truck today with the AC on and 93* F ambient, Ran about 13* cooler than it did before I switched out the Transmission cooler. I will have electric fans by the end of the week. Will see what happens.

Update. Truck now has 2 10" fans pushing through the radiator. Only 88* F today but it only got up to 204*. That is a 20 degree drop compared to before.