94 Blazer overheats

[454cid]

When you pull the thermostat housing on the 91 K2500 5.7, that I worked on, when you remove the thermostat and reach in, you can feel the bottom of the bolt hole. The bolt threads are immersed in the coolant, except for the threads of bolt that is in the intake above it.

So a through hole and not a blind hole. I'm not used to all the through holes on the sbc. Big blocks tend to have blind holes...thermostat, water pump, heads.

The rust builds in the entire cooling system and you saw it yourself on the Blazer. That rust will eat away at the edges of the head gasket where coolant passes thru the head gasket. Eventually the rust will eat thru if it already has a foothold on the gasket edges. If is not too bad and the system is flushed thoroughly, it can be ok. I have pulled head gaskets off that were eaten by rust but it takes some time. These are pics of what I pulled out of that same truck:

If the system is refilled with the proper coolant and has no more leaks it shouldn't continue to rust. I'd bet those headgaskets you encountered already had the damage done. Part of coolants job is corrosion protection.

 

[movietvet]

So a through hole and not a blind hole. I'm not used to all the through holes on the sbc. Big blocks tend to have blind holes...thermostat, water pump, heads.



If the system is refilled with the proper coolant and has no more leaks it shouldn't continue to rust. I'd bet those headgaskets you encountered already had the damage done. Part of coolants job is corrosion protection.

I warned her of the possibility of head gasket problems but none yet. IMO, it will. Maybe she gets lucky. You can refill with fresh coolant mixture, you still have a block with rust in it and the new coolant gets dirty and contaminated all over again. Not as bad, but it will still get dirty, to a point, over time. The fresh coolant is not gonna cure all just because it is poured in. Unless the heads are pulled, there is no idea of the damage already caused to those gaskets, by the rust in the system. That rust in the pics I supplied, is SEVERE.