Rear mount radiator setup

Hi there I have a remote mounted radiator and Im constantly overheating.

QUESTION: Should I have a swirl pot in the front with a rad cap and overflow AND in the back a coolant expansion tank with rad cap and overflow tank.

INFO: I currently have a thermostat coolant bypass in the front through a 1/4 inch line rerouting the coolant to the intake side of the water pump. In the back I have the coolant expansion tank with rad cap and overflow reservoir tank. Running stock pump on v6 4.0 OHV and 1.5 inch ID lines.

There is so much conflicting information on the internet I think you should add a course in this as well. Setting up a proper rear mount rad cooling system that can be easily bled.

You should only need one expansion tank / swirl pot -- mounted higher than any other water passage. But you can have two (but they should be higher than the local water passages)

I would instrument the car in the following ways:

-- measure differential pressure across the radiator. Make sure you know which way the flow is actually going. Often a change with a small aero piece (like a wicker on a high-speed stream just ahead of the duct exit) can increase the pressure drop and improve cooling. The radiator duct must be completely sealed (foam, silver tape, etc) -- all air that enters the duct must be forced to flow through the heat exchangers.

-- measure air temp on the radiator inlet. It should not be any higher than ambient.

-- measure coolant temp before and after the radiator. Is the radiator reducing the coolant temp that flows through it?

-- measure the coolant pressure (best if this can be logged fluctuation can be a sign of cavitation or air pockets.

The last bit of advice based on experience -- make sure the system is fully bled of air. The best setup I've found is the kits that replace the coolant cap with a stand-off and a large funnel to hold extra coolant. You fill the funnel, and run the coolant pump (love electric pumps) at high speed. Keep it up as long as bubbles are coming up from the funnel. If the car reaches normal temp, stop and let it cool down without removing the funnel. Repeat until there is no air. Cap system and move onto the tests I outlined above if you are still overheating.

For your system, I would put one of these funnels on each expansion tank.

I've found that a small amount of water wetter will also assist in bleeding cooling circuits as it helps to break the surface tension on the air pockets and disperses them.

Another issue that I had on a flat 4 engine was that I removed the heater core and throttle body heating circuits, and just blanked off the outlets in the cooling circuits when I did so. It turns out that by doing so, I caused the flow in those regions to stagnate and that part of the block overheated. I would have temp sensor and coolant pressure data log traces that had these strange, synchronised, bumps on it, that were being caused by the coolant flashing to steam, expanding against the coolant pressure and blowing high temp water/steam out of the stagnant area that then passed over the temp sensor. This area was then refilled with coolant, cooled down and then started the heating process over. This resulted in a failed head gasket and then a cracked head.

How long did it take for you to warp the heads?

David, so I can add a swirl pot with rad cap and overflow in the front just after the thermostat (see picture) and retain my current setup in the back. Should I have the same pressure (16psi) on both caps?

Hard to say without actually seeing the vehicle, especially as the plumbing in the photo's is very unclear. but some general points

Thing to remember is that any air in the system is going to rise to the highest point(s) in each run, and you should bear that in mind when running the hoses & pipe-work in the vehicle. It's also important when planning air bleeds,which can be opened while filling to allow trapped air to escape.

Where is your fill point? Is it what appears to be a terribly placed expansion tank to the left of the radiator, and if so, which side of the radiator is it plumbed into?

My initial suggestion is to modify things a bit - move the header/expansion tank ABOVE the radiator, so its filler isthe highest part of the whole sytem, running the hose to the top-most part the radiator. Modify the thermostat/hose to take a bleed fitting - doesn't need to be fancy, a (stainless) 6mm bolt in a tapped adaptor will work fine. That way you can fill the header/radiator and it should push the air through and out the bleed which can then be closed. Then run the engine while checking the coolant level.

The other thing that needs URGENT attention is the cooling fan arrangement - as it is the only effective cooling is from the area of the radiator directly under the fan - the rest is going to have to depend on convection airflow and cooling, which is negligible. Buy a secont fan, and fabricate a shroud that the fans can be mounted in, and that's sealed to the radiator matrix and the fans, so the ONLY air passing through theshrrousd is the fans drawing through the radiator matrix. On that, might be worth checking out if a double, or triple, core is available, for a bit more cooling.

Oh, make SURE there is a good stand-off between the fans and the radiator, so it can easily draw air from the whole area of the radiator - 50mm should be the minimum.

Thanks for the answer, I appreciate the input. Ill try to elaborate better on the setup

INFO: setup. My fill point is the header tank (16psi cap) that has the bottom port spliced into the coolant return. The radiator is a big dual pass, and has a rad cap with no spring so the rad cap port sends coolant to the upper port on the coolant expansion tank. The rad cap nipple on the expansion tank is connected to the overflow. The high pressure and low pressure side(output and return) run together under the cabin to the rear radiator. (all correctly connected)

PART SOLUTION: I will be getting a new radiator with a shroud and dual fans. And getting a swirl pot at the engine (with a rad cap and overflow) to bleed the front as you recommended(putting a bleed after thermostat).

QUESTION 1: I dont take offence but can you explain why the expansion tank/header tank is horribly placed? Its well above the radiator and the engine if you look at the photo. If you would do it differently Id like to get some ideas.

QUESTION 2: Should I decrease the plumping to 16AN size or 1 inch instead of the 1.5 inch, in order to increase flow. (Running big long lines and stock water pump could be causing water to move to slowly and not pressurizing enough to move air out)

I stand corrected, and apologise for being rude about it, I mistook the overflow tank for the header tank - it was a bit unclear - perhaps I should have said "unhelpful" photo' ;-)?

It may not actually be a problem with the coolant having air in it, I should have asked you if you'd done a basic "touch test" of the radiator - if there's actually air in it, you should feel it as cooler tubes at the top of the radiator and, if it's full of coolant, it should be roughly equal from the bottom tubes to the top, at least before the fan kicks in - if you have, or a friend has, a FLIR camera you can make a more accurate assessment of how evenly the coolant is passing through the radiator

If the former, you're going to need to address that problem, if the latter it suggests you're going to need to look elsewhere - such as the fans you're already planning to fit, which I think you're going to need to do regardless.

I wouldn't use a smaller diameter hose/pipe diameter, because that will mostly serve to increase the resistance to flow, which may lower the water pump's efficiency.

If it doesn't already have one, a 2, or 3, mm hole drilled into the thermostat sealing 'plate' may assist any bleeding.

I have 3 1/8 inch holes in the thermostat and a thermostat bypass (3/8 hose) to the lower radiator hose(i.e. bypass thermostat and route straight back to the pump)

But what is your opinion on adding another radiator cap at the engine? (i.e. swirl pot with rad cap after thermostat) same pressure rating as the one in the back or higher?

Pressure at the front, because of the restriction in the pipework, is going to be higher that the back, so if you go that route it'd need to be higher.

I emphasis that I can't quite grasp your full set up, but perhaps a swirl tank with a RESTRICTED return to the rear header tank would allow any air to bleed out to gather in the header, while still directing almost all the coolant back through the radiator?

That said, until you address the actual radiator and fan issue, I would avoid that complication, as I don't think it's where the problem lies.