water cooled manifold

[MaximG]

Mike, I'm saying I wouldn't do it your way, you can. I had a dodgy thermostat on my orange car so I did what you did to see if and when it opened. When it opened very hot water came OUT of the rad violently, I was shocked and felt daft for even trying it. When rallying in the 70s someone working on our Avenger scalded himself badly by opening the cap when the car was hot.

So my experiences may be isolated but they don't put warnings on rad caps for nothing.

And that's why I told him to take the rad cap off before starting to warm the Engine.

I also warned him that it may push water out the radiator.

Its a closed loop system that does pressurise due to expansion of heated water and releasing the cap when hot will do as you described. The Air and water in the system are going to stay in the system unless it finds a way out. The radiator cap is also designed to only vent when things get too hot and the Engine is in danger over heating.

I am more than aware of the dangers you described but I think in my description I gave ample warning of the possible outcomes.

Mike

 

[MaximG]

So when the carbs are removed a drop of coolant runs out.

Yes absolutely if they weren't silted up.

 

[Jimbo]

So the holes in the spacer/insulator at the bottom are to supply water? I didn't have those holes on my spacer and I've never taken the carbs off my current cars (Hitachi). So when the carbs are removed a drop of coolant runs out?

Thanks guys.

yes thats what happened to mine.
the holes in the spacer supply water to the late 240 carbs and onwards apparently
like yourself i have bought 2 new SU carbs to put on the manifold (awaiting throttle linkages) so hopefully no more fueling issues now ive blocked off the waterways.

heres a thread with some 240 carbs with the water cooling inlet/outlet
http://zclub.net/forum/showthread.php?t=24553

thanks again guys for the info and help its much appreciated.

 

[Rob Gaskin]

And that's why I told him to take the rad cap off before starting to warm the Engine.

I also warned him that it may push water out the radiator.

Its a closed loop system that does pressurise due to expansion of heated water and releasing the cap when hot will do as you described. The Air and water in the system are going to stay in the system unless it finds a way out. The radiator cap is also designed to only vent when things get too hot and the Engine is in danger over heating.

I am more than aware of the dangers you described but I think in my description I gave ample warning of the possible outcomes.

Mike

Mike, I had the cap off from cold and when the thermostat opened I was amazed at the pressure. Anyway you do it your way I'll do it mine - my point was that I can't recommend to someone to run an engine at working temp with the cap off.

 

[MaximG]

Mike, I had the cap off from cold and when the thermostat opened I was amazed at the pressure. Anyway you do it your way I'll do it mine - my point was that I can't recommend to someone to run an engine at working temp with the cap off.

Then just add a word of warning, just because you wouldn't do it this way doesn't mean it's wrong.

 

[Jimbo]

bit more info on the topic
http://www.ztherapy.com/technical_stuff/spotterguides/zcar/240spotter.htm

 

[toopy]

I bought a new thermostat housing, the bottom half, off ebay, which doesnt have the hole for the pipe that joins the manifold, so it looks neater/nicer than blanking it off somehow.

 

[johnymd]

I've always run the car up to temperature with the cap off to get rid of air. I did on one occasion take the cap off when hot and it was like a red hot geyser. Quite spectacular when viewed from a distance but wouldn't recommend it to anyone.

 

[Rob Gaskin]

Mike, I had the cap off from cold and when the thermostat opened I was amazed at the pressure. Anyway you do it your way I'll do it mine - my point was that I can't recommend to someone to run an engine at working temp with the cap off.

Right, I've run my car today from cold with the rad cap off. The level was quite low when cold - about half an inch above the core. I went in the garage for a couple of minutes and when I came out hot water was gushing out of the radiator in spurts and soaked the front of the car.

My immediate reaction was 'how do these guys do this without this happening'. I switched off and thought about it - perhaps I do have air trapped and it's finding it's way out violently.

So I let it cool, topped up and ran it for a long time with the cap off - no problem. I'm going to monitor this now and report back.

Mike, I may owe you a pint!

 

[Moriarty]

Water expands minutely when heated, (low coefficient of thermal expansion) conversely air expands dramatically (has a much higher coefficient) , because.... to quote Mr Jagger "its a gas, gas gas"

If you are seeing excessive pressure in a "closed" cooling system, then there is air in there, if there were no air, then there would be no pressure other than the small amount induced by the water pump (although technically its just moving water around) and the imperceptible amount due to the thermal expansion of the "water"......

Boyles law

"Gas" can get into a water based system fairly easily, sometimes due to the chemical decomposition of the metals used e.g. iron when it rusts...... Fe - Fe3O4 the iron gains oxygen from the water and "oxidises", releasing hydrogen in the process.

Running with the cap off for a short period is little different from opening the bleed screw at the top of a domestic radiator.

 

[Rob Gaskin]

................

Running with the cap off for a short period is little different from opening the bleed screw at the top of a domestic radiator.

Yes, but it can cause immediate boiling if the water is above 100'C, so that's why the caution.

 

[johnymd]

Does your car go reach 100'C with the cap off and at tickover Rob? If so then you may have a bigger issue than just air in the system.

 

[Jimbo]

would raising the front end of the car up on ramps aid expelling the air?
i used to bleed e36 bmws this way by having the passenger front wheel up the curb to coax air toward the rad bleed screw.

 

[Jimbo]

I bought a new thermostat housing, the bottom half, off ebay, which doesnt have the hole for the pipe that joins the manifold, so it looks neater/nicer than blanking it off somehow.

cheers for the heads up toopy i will be on the lookout for one.

 

[Rob Gaskin]

Does your car go reach 100'C with the cap off and at tickover Rob? If so then you may have a bigger issue than just air in the system.

Nowhere near John.

I was just pointing out that it's more dangerous taking a cap off than bleeding a house radiator. However I understand the expelling air bit of course.

Actually this Thread has taught me two things so

 

[uk66fastback]

Why anyone would EVER think of removing a rad cap from a hot engine is beyond me. I thought it was the first thing your dad always taught you as a nipper?

When I had a new radiator on my old Ford, I filled it and then ran it with the cap off up to operating temperature, and then refilled when it had all gone round the block etc and the rad level had dropped ...

Usual way of doing it I have always thought ...