Vortec 4200 coolant flow direction.....

cornchip

Well-Known Member
I relate things I know to things I used to see often. For example, my old 305 TBI V8 had the thermostat in the valley of the intake and flowed coolant thru the thermostat to the upper tank of the radiator (a down flow rad) making the lower hose was the draw to the water pump.

The 4200 has what I would dare call a lower hose from behind the PS pump coming from the 'upper' tank on the passenger side. I feel no spring in the hose as I *was* once used to seeing....maybe it doesn't always matter. That would make the upper hose (thermostat) exit to the bottom of the tank and pump 'upwards' keeping the upper tank full so it can be scavenged back to the engine. Do I have this right? No way this system works backwards to the way I think.

Seems odd and somewhat wrong to to the way I would like the system to operate. Why this matters to me is my swap project's cooling system. I have a new cross flow radiator with GM SBC hose locations....the upper location is on the drivers side to be connected to the thermostat. My draw is then at the bottom passenger where I think it's best.

Picture is oriented with top being up.

 

W4UWC

Active Member
I had been thinking about this as well. Just put together an Envoy and noticed the driver side hose was not as hot compared to the "upper" hose on the passenger side. Then realized the coolant flow direction wasn't bad I expected.
 

Blckshdw

Moderator
The 4200 has what I would dare call a lower hose from behind the PS pump coming from the 'upper' tank on the passenger side. I feel no spring in the hose as I *was* once used to seeing....maybe it doesn't always matter. That would make the upper hose (thermostat) exit to the bottom of the tank and pump 'upwards' keeping the upper tank full so it can be scavenged back to the engine. Do I have this right? No way this system works backwards to the way I think.
Coolant flows out through the upper hose on the passenger side, flows down through the radiator, and back into the block through the lower hose on the drivers side.
 

Reprise

Lifetime VIP Supporter
I relate things I know to things I used to see often. For example, my old 305 TBI V8 had the thermostat in the valley of the intake and flowed coolant thru the thermostat to the upper tank of the radiator (a down flow rad) making the lower hose was the draw to the water pump.

The 4200 has what I would dare call a lower hose from behind the PS pump coming from the 'upper' tank on the passenger side. I feel no spring in the hose as I *was* once used to seeing....maybe it doesn't always matter. That would make the upper hose (thermostat) exit to the bottom of the tank and pump 'upwards' keeping the upper tank full so it can be scavenged back to the engine. Do I have this right? No way this system works backwards to the way I think.
(on edit: Nevermind... see below)

Some bkgrd info...
By the time the LT1 came along, GM figured out that cooling would be improved through the engine if it were routed in the opposite direction from the SBC. Thus, the LS came to be known as a 'reverse cooling' engine.

Since the 4200 I6 came along after the LT1, GM probably adapted the same cooling flow through it, as they had for the LS engines. That's why you see it as working 'backward' to what you learned / experienced with the SBC motor. Hope that helps :smile:
 
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Mooseman

Moderator
In my early TB days when I was drinking the efan Koolaid, found out the top passenger side outlet was the hot coolant to tap in the fan controller sensor. So the coolant flow is as described by @Blckshdw .
 
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cornchip

cornchip

Well-Known Member
So I messed up a little in my initial thinking. When you talk conversion radiators it's always GM or Ford for hose locations....that being they are mirrored to each other. An issue with that regarding the 4200 is the lower hose is on top (lower hose is always has a bigger inside diameter). So you just can't buy something that exists without getting it customized. A stock Jeep radiator works for positions but falls short with incorrect hose ID's.

So I think I'll be fine even though it's not 100% ideal. I'm not pumping up from the bottom...but pumping sideways not fighting gravity. It's a closed system so it will fill to capacity after a few cycles if the puke tank is kept full (caps at the highest point in the system). It is what it is and will work.
 

Mooseman

Moderator
Is this for a GMT 360? There is a Dodge aluminum radiator that can fit with some work for mounting. Not sure exactly which one but you can see it's similar but has much more capacity.




And this one even comes with fans:
 

Reprise

Lifetime VIP Supporter
@Mooseman -- since you have experience with the 800's -- is there a 'retrofit upgrade' for those that you know of?

I'm inclined to boost cooling in mine (precautionary only), since the OEM rad is coming out when I start taking this thing apart -- but I know you're not an e-fan proponent, either.

I'll do some (more) research on my own, but was wondering if you knew of anything off top of head. Thx!
 
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cornchip

cornchip

Well-Known Member
Is this for a GMT 360? There is a Dodge aluminum radiator that can fit with some work for mounting. Not sure exactly which one but you can see it's similar but has much more capacity.




And this one even comes with fans:
It's a 4200 being swapped into a Jeep. Progress has been slow...but I'm picking away at it.

 

littleblazer

Gold Supporter
Some bkgrd info...
By the time the LT1 came along, GM figured out that cooling would be improved through the engine if it were routed in the opposite direction from the SBC. Thus, the LS came to be known as a 'reverse cooling' engine.

Since the 4200 I6 came along after the LT1, GM probably adapted the same cooling flow through it, as they had for the LS engines. That's why you see it as working 'backward' to what you learned / experienced with the SBC motor. Hope that helps :smile:
The LS does not use reverse flow cooling. The hose routing is the same as the GEN II engines but the heads aren't cooled first. The only engine to use it were the LT-1/4. The thermostat is on the inlet rather than the outlet on gen 2 and up engines though.
 

Reprise

Lifetime VIP Supporter
The LS does not use reverse flow cooling. The hose routing is the same as the GEN II engines but the heads aren't cooled first. The only engine to use it were the LT-1/4. The thermostat is on the inlet rather than the outlet on gen 2 and up engines though.
Confirmed & now corrected. Thx for pointing this out. Sorry for the error.
 

littleblazer

Gold Supporter
Confirmed & now corrected. Thx for pointing this out. Sorry for the error.
All good. I actually thought it did as well but one of the engineers a while back pointed it out to me. The chamber was efficient enough where it wasn't needed. However they left it so it is easy to swap should you want to. :thumbsup:
 

Flyboy2004

New Member
It makes no sense to me that the flow is up through the thermostat. What keeps it from closing when the cold water hits it as soon as it opens? Also, I flushed the system when changing the thermostat and refilled with water so I could run it and check for leaks. Now where can I drain enough water so I can fill with new coolant? This is on my '04 Trailblazer w/4200.
 
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christo829

Well-Known Member
It actually *is* supposed to close back down when the cooler fluid hits it, so the hot fluid that just got pushed in to the radiator has a chance to cool off. Meanwhile, the cool fluid in the engine has heated up, and the thermostat opens up again. Lather, rinse, repeat until most of the fluid has reached an average operating temperature. The thermostat wil continue to open and close to some degree to regulate that temperature, since too hot will bake the engine, but too cold will cause it to not run right. Too cold usually means it's failed open, allowing full unregulated flow, too hot would mean it's most likely failed shut and isn't opening properly to allow the fluid in to the radiator to cool off.

As far as where to drain it, the last time I drained mine I just popped the bottom hose, let it drain, then squeezed the top hose a few times to see if it was still holding fluid after I'd drained enough to lower it past the thermostat housing. If you're *really* lucky, your radiator has a drain petcock! If not, your other option is to get a fluid pump with a small hose to suck out the water from the radiator and replace it with coolant.

Good Luck!

Chris
 

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