Eggplant Jeff

My car (92 305 L03) takes a LONG time to warm up in the mornings. I started wondering why this was, and after looking at it a bit, noticed something.

The heater core hoses seem to be the problem. On my car (I guess to simplify hose routing?) the source of coolant for the heater core is the intake manifold. The sink (where it goes after exiting the heater core) is the radiator, there is a special return hose just for the heater core, that dumps coolant in just below the radiator cap. There is a bypass valve for when the heat select lever is off, but all that does is shunt coolant direct from source to sink, bypassing the heater core.

What this means is, as SOON as the engine turns on (thermostat open or closed makes no difference), coolant begins flowing from the intake manifold into the radiator. Now, it is entering the radiator on the passenger side, travelling (more or less) straight down to the lower radiator hose, and being sucked back into the water pump, but it still must be losing a LOT of heat mixing with the other two gallons of cold fluid in the radiator.

Now, older cars had a different hose routing. They ran a hose direct from the water pump to the heater core, and returned the coolant into the intake manifold. I am thinking of modifying my car to work this way as well.

My water pump has a port on it (currently with a plug in it) for the older style hose. I'll need the screw-in attachment thing for the hose (the thing you clamp the hose to), and I'll just re-route the hose that currently returns coolant to the radiator, to source coolant from the water pump (which will incidentally reverse the direction of coolant flow through the heater core). Oh and I'll have to block the port on the radiator that the return hose currently attaches to.

Now, my concern is with the reversal of coolant flow through the heater core, and through the intake manifold. I can't see where it would make a heck of a lot of difference, but does anyone think otherwise? What potential problems might crop up?
Any thoughts on this modification?

It also seems like this would improve cooling in hot weather, since ALL hot coolant would be forced to go through the radiator, rather than some (all the coolant that would have gone through the heater core) simply being returned on the passenger side of the radiator and going straight back to the lower radiator hose again.

Vader

EJ,

You could switch to the older style heater hose routing without too much trouble. Doing this would eliminate the wot water valve, and provide you with a little faster coolant temperature rise. In order to make sure you don't battle yourself with the air conditioner in the summer, you'll have to be sure the heat damper closes fully. That could be a large task, since the ductwork and dampers are in front of the dash.

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Later,
Vader
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RB83L69

I've used the 2 routings interchangeably on my car, and it doesn't seem to make the slightest difference. It certainly doesn;t cause any problems.

If you think about it, the "cool" water from the heater doesn't really mix with the radiator water at all. The water pump fitting and the rad fitting are pretty much at the same point in the system: at the suction inlet to the pump.

I'd be more inclined to think that your thermostat is stuck open or something like that as the cause of your slow warm-ups.

Changing the hose routing won't affect hot weather cooling, as the return water from the heater core simply dumps into the suction side of the pump a little closer to the pump. No real difference there.

You might want to check and see if it's possible to use a heater control valve in your application; that would prevent any coolant flow at all while the stat is closed.

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