Tau

n/a '88 SE

I started the car with the hood up. As it started to warm I noticed coolant leaking from the filler cap.

Backgound: About 50 miles (10 months) ago I installed a Koyo radiator. The radiator cap is rated at 1.3 bar. After the first post upgrade drive, when the engine cooled, I noticed that the upper radiator hose was collapsed. It looked as if one sucked the air out of a straw with the other end blocked. I opened the filler and the hose popped into shape. Then I added fluid. Where did the fluid go?

I understand that during pressurization of the system the Radiator cap plays a part in dumping fluid to the reservior to maintain pressure. When the system cools fuild should return to the system from the reservior. (I really don't understand the return mechanism. Any explanation would be welcome since the plumbing doesn't support that behavior as far I can tell.) It seems to me that if the return was blocked in some way that radiator hose could collapse as the fluid cooled.

Today's observation leads me to believe that I need a new filler cap. However I wonder what role the 18lb radiator cap may have in the end of the filler cap's life. I am sure that the thermostat was not fully open when I noticed the leak - the fluid was hot before the cap an cool after it. So pressure should not have played too much a part...right?

Could the new Koyo and its higher system pressure have contributed to the failure of the cap? I hope to replace the cap with a Mazda part. Will the new one fail to keep pressure or fail prematurely?

texFCturboII

iTrader: (17)

I'm having the EXACT same issue with a godspeed radiator.

clokker

iTrader: (2)

The Koyo rad has no "system pressure", neither higher or lower...system pressure is solely a function of the cap.
If you are both certain that the hose from the rad to the overflow tank is good (and the connections) then it's possible that the overflow barb on the filler neck is improperly positioned.
If it is not uncovered as the filler cap retracts from pressure, the recovery tank system cannot function and the cap will leak.

Tau

Thanks Clokker,

I got the part about 'system pressure'. I'll take a look for that "overflow barb" thing. Maybe it'll be that quick a fix. Regardless, it will ge me a chance to figure out that plumbing. More later...

Its wierd that the pressure would rise so much on a warming engine. The radiator, and cap, were cold so I figure 1/2 the fluid volume (maybe more) was still cold. The filler cap must be worn in some way to give way so early in the heating/pressure cycle.

texFCturboII

iTrader: (17)

I think it will be that quick of a fix at least with that problem for you... My setup to the overflow tank is kinda whack right now; i'll try and fix it tomorrow so i can tell you if that fixes it or not. At the moment I have two overflow barbs, one at the radiator and one at the filler neck off the water pump, with two lines tee-ing into one. Makes perfect sense that it is leaking because of that now. The cap on the radiator is lower in the system than the one on the water pump. It's simply gravity preventing the one at the radiator cap from doing its job, at least that's my hypothesis.

clokker

iTrader: (2)

Gravity has nothing to do with it...at 13psi pressure, the coolant would climb a hill to get out if it could.
If you have two fill ports in the coolant loop, only one should be pressure release capped and there would be only one overflow tube.
The t-fitting is superfluous.

texFCturboII

iTrader: (17)

So the other one could just be capped off? I've got another plastic "cap fitting" for the filler neck w/o the nipple that I'm going to replace anyways.

clokker

iTrader: (2)

One of two- doesn't really matter which- should have a pressure cap, the other shouldn't.
You could easily make a block off plate for the port on the thermostat neck and use the radiator port for overflow.