280i radiator cap pressure?

[440Interceptor]

Been having a few issues keeping the car cool, sometimes even when cruising on the freeway. New water pump, new hoses, clean rad core, new electric fan on thermoswitch.

Checked today and the overflow tank has been losing a little coolant too, so I wanted to confirm cap pressures on the V6 with the forum.

I have a cap on the expansion tank - 16 lbs. The Bible says this should be 13 lbs and my Capri 2.8 workshop manual says 12.0lb to 15.7lb (!).

However, I have a 7lb cap on the radiator itself and I'm not sure whether this is right or not...The Bible is silent on this cap.

My thinking is that once pressure exceeds 7lb the rad cap will open and send hot coolant to the expansion tank, and from there out of the bottom outlet and into the thermostat housing and back through the engine - without going though the rad!

Because there is a hose from the rad cap neck to the expansion tank it follows that there should be a sprung cap, but what should its pressure be? Closer to but not more than 13lb? Maybe they should both be 13lb?

Any thoughts guys?

[440Interceptor]

Thanks mate, yeah it makes sense. I'll grab two newies.

There are two inlets to the header tank and one flows all the time - from the T piece in front of the plenum. The other will only flow if the rad cap spring lifts.

Will report back to others can use the info.

[440Interceptor]

taz turbo said:

My car has a blanking cap on the radiator and a pressure cap on the expansion tank.

A pressure cap on the radiator would mean the system wouldn't bleed air until the pressure cap on the radiator opened, as the pressure cap on the radiator would also see pressure on the reverse side it's never going to open.

Chris.

Thanks for the post Chris, it's got me thinking too. Agree that there would be pressure on both sides of the seal so the rad cap won't open.

But with a blanking cap on the rad, there will be a permanent flow from the top outlet into the header tank which will bypass the rad resulting in less cooling. Is that not a problem?

[440Interceptor]

Thanks guys. Andy, I'm gonna have to read that a few more times until it makes sense to me..

I don't need a heater here so I bypassed it completely, so no T piece between the header tank and the thermostat housing.

My hoses look like Zigs except the header tank is on the drivers side and so is the alternator. I assume you had to make some room and put the battery in the boot Zig?

I put a blanking cap on it yesterday but haven't tried it out yet apart from once around the block to check for leaks.

[440Interceptor]

Alright, I think I should grab some new photos and maybe do up a diagram too. Picture = 1000 words and all that. Need to get it right for summer. Thanks gentlemen, watch this space.

[440Interceptor]

Sardonicus said:

mrzigazaga said:

Just called the Ford guy and he confirms that it should be a blanking cap on the rad and a pressurised cap on the bottle...

Thats how it was on the Ford cars fitted with the 2.8i Cologne motor e.g the Capri

Ok, that's probably why the Capri manual only mentions one pressure cap then...