Best coolant type for cast iron block engines?

[FTTSHO]

I just did a coolant flush on my 2001 Chevy Blazer with the cast iron 4.3 Vortec. I put in Prestone Max Coolant, which is supposedly their longest lasting best coolant, and it’s a HOAT type based on the research I’ve done. The previous owner used Dexcool Orange coolant and I’m assuming quite a bit of tap water was also used, because I had severe rusty coolant problems and overheating problems when I first bought the truck over 2 years ago. I flushed the system last year, and put in regular Prestone AMAM coolant. I got the problem completely taken care of a week ago with Thermocure Evaporust, and I flushed all the coolant components individually with distilled water. Now the truck has Prestone Max coolant in it.

I was talking with my buddy today about the coolant flush I did, and a topic came up about what type of coolant is best for cast iron engines. He says traditional green IAT or OAT is best for cast iron. From what I can tell, HOAT is the best for all applications now.

What are your thoughts on what type of coolant is best for cast iron engines? I want the best one in my truck, because I want to avoid any rust issues with cast iron.

Thanks!

 

[JavierH19]

As for what type I can't say but as long it's a better kind which can be universal like prestone platinum or the max which looks to be the same it's fine. I wouldn't use a cheap 5 year coolant only the 10 or 15 year ones but change at half the interval or less on the bottle. But if you want to preserve an iron block use a bit heavier coolant concentration to let there be more anti rust and impeller lube floating around in there and change it more frequently.

I already did my sierra with prestone platinum last year but I need to do my yukon which for having 341k on its 21 year old iron block without ever giving me heater core or head gasket issues on nothing but universal stuff you can't knock it. I've changed two water pumps due to them leaking but having a fairly clean impeller and one radiator but the plastic cracked on that one. Heater core hasn't been flushed and still delivers heat quickly.

I've been tempted to try an anti rust additive but it's likely snake oil.

 

[Snagglefoot]

I have being using Dexcool for 17 years changing every five years in an iron block 6.0. No rust at all. There is no problem to solve as far as I am concerned. YRMV. In my 20 year old iron block Ford Taurus I have been using Prestone AMAM for the last 8 years since I bought it used with 50,000 miles. No rust. The commonality? 2EHA.

 

[JHZR2]

I’ve been using dexcool in my 1998 S-10 ZR2 since new. Still all original cooling system. Clean as can be.

Use the right radiator cap and keep it topped up. Change the manifold gaskets if needed. It will be perfect forever.

Defile the system with anything else and you may have issues…