overflow tank with 5.3 swap - how to route to radiator and steam port?

[paradigm]

I have an '86 Monte Carlo SS with a truck 5.3 LM7 swap. The prior owner installed a Mazda 3 overflow tank which seems to complicate things with the following:

A on the overflow tank goes to the high side nipple on the radiator.
B on the overflow tank goes to the low side nipple on the radiator.
C on the overflow tank goes to the steam port passing through the throttle body.

I want to simplify the setup with either the factory non pressurized monte carlo overflow tank or a Dorman 603-001 overflow tank.

I am going to re direct the steam pipe to the high side on the radiator tank.
I am going to use the blue nipple on the radiator tank to feed the monte carlo or dorman overflow tank.
I am going to cap the lower nipple on the radiator tank.

Should I replace the vented fill cap on the radiator with a solid one?

 

[Sweet_Johnny]

I'm unfamiliar with the swap but what you've laid out makes sense to me. I don't see an issue but might be missing something. As for the cap, that's up to you I guess. I used to run a vented cap but it's not a big help in any way unless you plan on removing it while hot. I just go for the highest pressure rating available to prevent boiling.

 

[paradigm]

I reinstalled the OEM MC overflow tank to the highest nipple on the rad tank, steam port from engine to the second highest nipple on the rad tank, and capped off the nipple towards the bottom of the radiator tank.

The Stant rad cap is rated for 13lb and has a vent on it, I may replace it with a higher rated cap that is solid / no vent.

Slowly the engine bay is getting cleaned up and the car is becoming more functional.

 

[78Delta88]

I am limited in that I have not done an LS swap. I have the 86 which was originally going to do that with the single turbo but never happened. However the friends I have that have done the LS swap I can ask. Of course there are several on this forum that have done the LS swap.

I just look at the engineering side of the cooling system under pressure. So if you are running a 15 psi rated system, and you want to stay with that, you need a 15 psi cap for the radiator. The overflow tank needs to be mounted at a proper level, so that when the system cools down it keeps the proper level of coolant in the system.

Overflow is only an issue when the system becomes too hot and over 15 psi and excess is voided outside of the system. This should be the same for steam as the hot coolant which is no longer under pressure can flash to steam. If you want to capture and condense that steam so it can be recirculated back into the system then you have to have a method to do that. Otherwise it's voided to the outside environment.

So basically what you need to do is understand the system in use for the LS engine and build your system around it accordingly. If the LS goes above 15 PSI you need to have a complete closed system which means a cap on the radiator that will not open until it matches the LS engine's maximum pressure as per its original engineering.

The other problem you will come into though, is if your radiator is only rated for 15 psi and the LS engine is running normally at (example) 20 psi you'll eventually fatigue the radiator and it can fail.

The lever on the cap you have is just to release any excess pressure prior to removing the cap. On a cold engine it's a non issue.

 

[64nailhead]

Much easier solution is to drill and a tap an 1/8 npt fitting into the top of the water pump. Run your factory coolant reservoir to the nipple on the radiator. The only issue you will encounter by doing this is bleeding the air out of the system which if and when you evacuate the cooling system and/or engine. You will have to ‘burp’ the air out of the system whenever you empty the system - it’s a process, but very easy. And it leaves a much cleaner looking engine bay.

 

[64nailhead]

Here’s a couple of pics of how I have setup all of the swaps that I have done.

 

[Rt Jam]

The previous owner installed the Mazda tank because he understands a pressurized recovery tank is not the same as a vented reservoir.

The steam port connection is to remove hot coolant from the cylinder heads. In a high performance engine, the idea is to remove as much head from the heads as possible. To the radiator top tank is the best place. An 85 radiator will not have that port.

 

[64nailhead]

The purpose of the steam ports is to remove air/steam from the highest point of the motor. The purpose of a coolant pressure tank is to allow air to be removed from the cooling system, i.e. heater core(s), etc. and for easy filling of the coolant system without having to ‘burp’ the system repeatedly. The OEM’s put a lot of effort into design for f the coolant system. But it isn’t needed, just makes it simpler to refill the cooling the system.