As some of you know, I added a second engine in the back of my shadow. I'm having some rear engine cooling system problems when on the free way. Temperatures are close to 230, and I would like to lower that about 15 degrees.

I know the issue is airflow through the radiator, and I know cutting up the body and adding scoops and the like will help direct ambient air to the radiator, but I don't want to add scoops and cut the body to take away any of the stock appearance.

So I thought I could add a small radiator to the upper rad hose in parallel, to help get rid of that little bit more heat. I found a small rad from a motorcycle that uses 3/4" inlet and outlet and has a rad cap so it can be bled fairly easily. It has a 10x10 cooling surface area and that's going to fill up about all the space I have available. It will draw fresh air from the right rear wheel well and it has a small fan to help it cool.

Now onto the tricky part, I need to know what you think is the best way to get enough coolant flow through the motorcycle rad without restricting the water pump too much.



These are 5 ideas how to plumb it in. In all pictures, the upper rad pipe is 1.5" OD and the radiator inlet and outlet are 3/4" ID.

The reason for 1.5" rad hoses are because they're made from exhaust pipes and that's the smallest diameter the exhaust shop had. I think it necks down to 1.25" at the thermostat housing, water pump inlet and the radiator inlet and outlet.

Picture 1 is pretty straight forward, but I don;t know it would direct enough coolant to the rad.
Picture 2 is similar, but adds the motorcycle rad hoses into the coolant path,
Picture 3 is the same as 2, but changes the angle of the cut on the tubes.
Picture 4 is like 3, but adds a washer acting as a restrictor to help direct more coolant to the motorcycle rad.
Picture 5 is similar to 4, but doesn't have the motorcycle hoses in the coolant flow. It's also easier to weld straight on.

So what do you think??