David Butcher's Datsun Roadster Cooling System

This story is still being created. Here is the draft so far...

I suffered through an overheating car for two years. A replacement head plus gasket, high-capacity thermostat, and a radiator clean/rod cured the problem, BUT - I 'invented' a way to live with it until I was able to do the major work.

The symptoms were:

coolant was getting pumped out by a very slow leak INTO the cooling system (probably exhaust gasses) and the car would gradually run hotter and hotter until it boiled over. Here is what I did:

<-- front of car

       |- upper radiator hose
  ---  v
  | |================O
-----               -----------------------------------
|000|<-ovrflo tnkXX |                                 |
|000|            XX |<- water pump                    |
|000|  |-HERE!!  XX |                                 |
---*-  v         v  |         engine                  |
  |**************v  |                                 |
  | |            v  |                                 |
  | |            v  |                                 |
  | |=============  |                                 |
  | |        ^      -----------------------------------
  ---        +- lower radiator hose
   ^radiator

ASCII drawings are a pain.... here is a picture.

I replaced the lower radiator hose with a copper/rubberhose combination. The copper was 1 1/4 inch and looked like this:

	   v<- additional elbow here to make right angle to water pump *
	   v
	   v
	   v
	   v
	   v
============
<- to lower radiator opening, about 4 inches of rubber hose

* right at the top of the elbow, I added a 3/8 inch connector - I simply drilled the elbow and soldered it in. I drilled where the elbow was slipped over the riser tube so the copper would be double-thick

<- to water pump
  ------------
  -|          \
  -|          |
  ------\     |
	|||||||
	||||||| <- drill through here
	-------
         |||||
         |||||
         ||||| <- to lower radiator hose
         |||||

Then, I drilled through the bottom of the coolant overflow reservoir, and added another 3/8 piece of pipe poking through the bottom. I reinforced it by drilling through a penny and soldering the whole shebang to the bottom of the tank. I ran the tube into the tank approximately the same distance as the original overflow tube, which I left intact. If you can picture this, there are now two identical tubes entering the bottom of the overflow tank, but at opposing corners. All that is left to do is to connect a short length of hose from the new overflow tube to the connector on the waterpump intake tube. Here is the flow through the overflow tank now:

                 XXXXXXXXXXXXX
                  |         |
       +-------------------------------+
       |                               |
       |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~|
       |                               |
       |                               |
       |                               |
       |       gasses go to top        |
       |   ^                     |     |
       |   |                     |     |
       |   |                     |     |
       |                         V     |
       |  |||                   |||    | 
       +-------------------------------+
	  |||                   |||
	  |||                   |||
	  |||                   |||
Overflow from radiator          ||| <- to intake side of water pump
	(intake)		(outflow)

Instead of being a "dead end", the overflow tank is now part of the circulating cooling system! The low pressure side of the water pump keeps a constant flow of coolant from the radiator overflow into the overflow tank, then back into the waterpump. The result is that any gasses in the system are eventually purged through the overflow tank, which was not happening when the tank was a "dead end" - expansion would stop when running temp was reached, and then the gasses would gradually accumulate in the radiator and the engine block, pushing coolant out of the system. I used to watch the coolant level slowly drop by pulling over and checking it on the way to work.

The whole modification took about a day, and I have never had any sign of trapped gasses in the cooling system since. If there is anything in there it ends up in the overflow tank where it is shoved out through the normal expansion/contraction action of the coolant when I park the car and drive it.

Several additional benefits:

Topping the overflow reservoir with Redline Water Wetter or antifreeze results in immediate mixing due to the constant flow through the reservoir

Cooling capacity is increased (a little) because the overflow tank is now a "mini-radiator" - radiating heat from the coolant flowing through it

That lower hose (moulded and difficult to find) is now a straight 4 inch piece of radiator hose, and the part going into the water pump is a straight 2 inch piece, so no more hose matching problems...

The copper radiator pipe probably radiates heat better than the hose, so there is even more cooling capacity

I hope this all makes sense. I ultimately replaced the head, gasket and had the radiator rodded. I needed to do all those things anyway, but I left this setup in place because it still seems to be a better design that stock.

David Butcher 67 1600

The thermostat is from

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