Back-Flush and engine petcock...

Thank you in advance for any help.

I am looking to back-flush my son's 1996 Chevy Blazer 4.3 V6 (w).

I have Chilton's book for this car and it's difficult deciphering some of the information on this topic. In Chilton's it mentions (in the
General Information and Maintenance part) "Open the radiator and engine petcocks (located near the bottom of the radiator and engine block, respectfully), or disconnect the radiator hose at the radiator outlet.

Does anyone know if this engine has a drain plug and if so, where is it located. I bought Prestone Flush 'n fill kit. If there is an engine drain would it be better to forgo the kit and use the engine drain?

I would appreciate any other info you may have. I will be working on the car Thursday (tomorrow) morning. I hope to get the correct heater hose to cut.

"Rex B" wrote

I think I see what's happening. You are suggesting putting the tee into the heater hose that connects to the intake manifold and assuming that the water will flow back into the intake manifold. I'm not sure that this will happen....more like the water will flow both into the heater core and the intake at the same time, which would end up possibly stalling the flow of water thru the heater core.

I'm suggesting that we pull the return heater hose off at the water pump or radiator (wherever it happens to terminate at the engine/rad) and then push water in a reverse direction back thru the heater hose. So I guess we both are attempting to accomplish the same thing,
I'm just not sure that the tee will accomplish the back flush of the heater core (which is why I never use a tee).

I think if you put water into the lower hose area of the water pump (which is where the heater hose typically connects), you will indeed reverse-flush the radiator, but not the engine. The flow would go like this:
Rad hose into bottom of rad
Bottom to top of rad out upper tank then exit at radiator filler neck.
All water going the other way through the block and heads would be in the normal direction of flow, but would be stopped (except for bypass) as soon as the cold water hits the thermostat.

If you introduce water at the manifold, the cold water hits the thermostat and prevents it from going straight out to the radiator (the normal flow). If you also close off the heater circuit (once it's had time to flush) then ALL of the fresh water must go into the heads, down through the block, and then out the lower hose to the radiator bottom tank.
Rex in Fort Worth

that connection is my recollection of the instructions on the package, although years have passed since. But it makes sense to me: The flow is typically (LS1s etc notwithstanding)

Back of water pump into block
Block up into heads
Heads into manifold
Manifold to top of radiator (inlet) by way of thermostat.

Heater hose from manifold pipes hot water back to heater core, then returns it to the water pump inlet/lower hose spout.

By introducing pressurized water (garden hose) into the heater hose in the manifold, you are reversing the flow of water. It would go into the head, then the block, and out the water pump in reverse flow, then up the radiator and out the filler neck. The cold water keeps the stat closed so it doesn't just run out the top hose.

IF you put it in the other heater hose as you suggest, you are just introducing cold, clean water into the normal flow.

Am I missing something ?
Rex in Fort Worth

Use the kit and follow instuctions for the very best results. Be sure to tap into the heater hose coming out of the manifold. Done properly, the water flow is reversed which is what you want.

Rex in Fort Worth

"Rex B" wrote

Rex, I'll have to disagree. You want to remove the return line which is the heater hose that goes either to the radiator or the water pump.
The intake fitting is always the pressure line.

Frankly, those tee kits are nothing but junk. Much better to just remove the heater hose at the water pump/rad and put your water through there. The tee does make it easier for the novice, but then you have two extra connections that can leak. Of course this is simply a personal opinion...this could not be made into any kind of "orthodox doctrine" within the vehicle repair world as far as I'm concerned.