Vortec 454 Heater Core Bypass

Hey y'all!

I bought a 454 suburban about a month ago, and today I was on my way to buy some seats from a guy when I noticed my water temp was high. I coaxed it home, and found that it is leaking from somewhere in the area of the heater lines.

What a rats nest of hoses!

This vehicle is just the funvee, not a DD. So I want to bypass the heater core.

Do I understand correctly that all I need is to cut the lines from the radiator, then from the intake manifold, and install a 3/4" barbed fitting to join the two?

I did a forum search, and got lost in all of the posts. I'm sure one exists explaining this, but I couldn't find it. It's more confusing than the tangle of hoses going to the front and rear heaters.

Thanks guys!

Yes, what you said will work if you really want to bypass the heater instead of fixing it.

I'm not familiar with the ports on the 454, but your truck will either have a loop between the intake manifold (high pressure) and water pump inlet (low pressure) or between the intake manifold and the cold side of the radiator. If you can, run the line between the manifold and the water pump. Running straight back to the radiator works, but will make the truck take a very long time to warm up and maybe not ever completely warm up driving around at low load as you are creating a way for coolant to bypass the thermostat. This is not good for engine life, and the ECM may also have some problems with running in warmup all the time. At a minimum, fuel mileage would be even worse than it already is.

Regardless of which routing you use, I would suggest finding some way to orifice the hose. Usually I end up welding a washer into a fitting somewhere with a 1/4" ish hole in it. This just limits the bypass flow and ensures that you still have good coolant flow through the rest of the engine and not just through your newly created path of least resistance heater core bypass.

I used a straight barb fitting with 3/4" on one end and 5/8" on the other and connected the port on the radiator to the intake manifold with short pieces of hose. I bought it a NAPA. Its plastic which makes people a bit nervous.

You could instead plug the intake and plug the radiator port, which is what I would do if I intended it to be permanent. You would need a 1/2" pipe plug for the manifold and a plug that's like a rubber cap for the radiator......those can also be had in silicone online and will last longer than rubber.

In either case there is no worry about the truck not heating up.

Your mention of a rat's nest makes me think that maybe you have rear heat....I dont know how all the hoses are set up, but I'm sure you could just bypass that and keep the standard front heat.

454cid said:

I used a straight barb fitting with 3/4" on one end and 5/8" on the other and connected the port on the radiator to the intake manifold with short pieces of hose. I bought it a NAPA. Its plastic which makes people a bit nervous.

You could instead plug the intake and plug the radiator port, which is what I would do if I intended it to be permanent. You would need a 1/2" pipe plug for the manifold and a plug that's like a rubber cap for the radiator......those can also be had in silicone online and will last longer than rubber.

In either case there is no worry about the truck not heating up.

Your mention of a rat's nest makes me think that maybe you have rear heat....I dont know how all the hoses are set up, but I'm sure you could just bypass that and keep the standard front heat.

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Thanks, that's exactly what I needed to know. It likely won't be permanent, so I'll go the barbed fitting route. I'm going to go out today and pull all the old lines out to see if the leak is a hose or the heater valve. I DO have rear heat. At least...i did.

See if you can borrow a cooling system pressure tester from Autozone, and pressurize the system with the engine off, and look for the leak. You might as well check the weep hold on the pump while you're at it.

454cid said:

See if you can borrow a cooling system pressure tester from Autozone, and pressurize the system with the engine off, and look for the leak. You might as well check the weep hold on the pump while you're at it.

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Good advice! I was trying to figure out a way to guarantee the leak was the heater valve-I forgot they had those. I guess if I'm going to mess with this, I might as well fix it right.

C.E.Divine said:

I might as well fix it right.

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EXCELLENT idea.

Reviving a little bit of an old discussion here...

Does anyone else have trouble finding a heater core bypass valve that doesn't start leaking? All I seem to find are cheap plastic ones. I had one nearly cost me my engine once when it broke in half without warning on the interstate, dumping all my coolant in a couple seconds. New ones seem to last a couple years at best before they start dripping from a joint or the shaft itself. I have a 1996 5.7 Tahoe BTW, no rear heat.

I always just kept my in the loop until it was winter. Mostly because the blend door flaps have a rubberized end that’s broken on pretty much every truck at this point. So I get a colder AC when the heater core is bypassed and looped


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I am going to do the same, as I am annoyed with having to change the valve every 6 months, I have not tried a GM replacement part, thought about ordering one, to see if it holds up. Then again it could just be Chinese made garbage. I will update.