I have a 1996 Blazer 4.3. My heater core had a slow leak so I bypassed the heater by joining the 2 hoses together with a 5/8 to 3/4 adapter. 2 years later one of the hoses has sprung a tiny leak. I've read online that it's possible to cap off the heater hose fitting on the water pump as well as the return fitting on the intake, and just remove the heater hoses altogether. Does anyone know if this is true? Or will it cook the engine?

 

I am pretty sure that you should not cap that off. The heater hoses i believe are an essential part to the cooling system. If you don't care about heat just run a hose from the water pump to the intake fitting.

 

I also wouldn't recommend capping the heater hose fittings. It shouldn't "cook the engine" if you do, but it will put added stress on the water pump when the engine is cold.

When the engine is cold and the thermostat is fully closed, the water pump draws water from the bypass hose and the heater return hose. The heater hose is half of the "bypass path" for this engine when the thermostat is closed. Without that hose flowing, the water pump will have more suction and resistance to overcome to circulate coolant through the block in a cold engine. The possible downsides are water pump failure or serpentine belt issues (slipping, wear).

If you want a "cleaner" bypass, I think you can find a smaller outlet fitting, and use a single piece of 5/8" hose for the bypass. IIRC, the pipe threads in the manifold are 1/2NPT. Look for a 1/2NPT to 5/8 hose barb fitting. That's a common part for heater bypass on small block Chevy V8's (either Vortec or older SBC) as well as on this 4.3L V6.

 

Thanks for the replies. To confirm, a 1/2NPT to 5/8 hose barb fitting will thread right into the intake without any modifications?

 

I'm sure it's a standard NPT size. It looks like 1/2 inch to me.

When I did all my intake manifold stuff, I took my old rusty fitting to the plumbing supply place and handed it to the guy there. He tried it in a pipe fitting and it fit perfectly, walked back in the warehouse and brought me a brass one and said that's all he had in stock. I asked if he could get me a stainless one. He said it would take a couple days, but he could get a stainless one for me.

Mine has the barb for the stock 3/4 inch outlet hose to the heater, but if you're just bypassing straight to the water pump, you could get a 5/8 inch barb.