3C water hose

[CHRISEEBOY]

Afternoon everyone.

I've just been working my 3C for about an hour at quite high revs then turned it off. As I was walking away I heard a bubbling noise, then a pop, then the sound of water hitting the ground. It turns out the top hose on the rad (I think its the return), had popped off and dumped coolant on the the floor. Not a huge issue in its self but I'm wondering if it is a simple case of the jubilee clip holding the hose not being tight enough or a more serious problem elsewhere?

Does any one know how much pressure the coolant system on these old girls runs at? Should the coolant even reach 100 degrees? What might cause my engine to run so hot that it boils the coolant?

Any help/advice will be much appreciated as usual

[MrF]

It should be regulated by the radiator pressure cap which irrc opens at 4psi and should dump the excess pressure out the overflow tube into the expansion bottle.
If she was working hard, then you shut her off and was walking away, could be that you removed the cooling air that was keeping it from boiling because the fan stopped turning. I would try putting the hose back on, top off the coolant, make sure the cap is the correct one and opening & that the overflow on the radiator isnt blocked and keep a eye on the level in the expansion tank to see if it happens again.

For other causes other than being hot and turned off, well, literally anything that causes it to run hotter than normal, or presurise the coolant system.

[CHRISEEBOY]

Thanks MrF. There is indeed a small hole just under the rad cap, but no hose or expansion bottle. This hole does not appear to be blocked as it looks like water has been leaking from it prior to the hose being blown off. Not sure if the cap has any kind of pressure valve on it.

[Jeremy Rowland]

Chris I would also use a new jubilee clip for good measure, let us know how you get on.

Jeremy

[CHRISEEBOY]

OK Jeremy, will do.

I'm going to take this opportunity to run a bit of degreaser around and flush out all the junk then I'll put a new clip on and let you know.

[MrF]

I was missing the expansion tank too, but I got a really cheap generic one off ebay and some tube and added it. Sadly it looks like the barb that the tube linking to it pushes onto has been snapped off that hole by a previous owner already.

If you pop that cap and take a look at the seat that the cap pushes onto, due to the shape of the radiator top tank its possible the seat is distorted & the cap isnt sealing at all. In which case you might have been at 0psi and quietly steaming off coolant the whole time. Water under 4psi of pressure boils at 112c not 100. They can run like this for a while provided you keep the level topped off occasionally.
It also looks like someone might have soldered a new cap neck on though unless they were chasing a leak caused by the distortion with all that solder blobbed about. This is how my top tank was also, where previous owners had stood on top of it (its only thin sheet formed into shape) and I ended up soldering a new cap neck I found on ebay into the tank to sort it out. The 3c2 I broke had a rad that was also bent and twisted where the cap seals in a similar fashion, it seems fairly common.
I posted a pic of my homemade pressure testing rig, which consisted of some inner tube bunging up the ports, and a valve with rubber round it in the other, and a motorcycle suspension pump, so here it is again


I would also guess the port where the top hose connects is a funny shape with all the distortion around it, so it might be marginal and as Jeremy says a new jubilee clip (or 2) might help.

The pressure relief spring is built into the radiator cap itself, its the bit you compress when you push down and twist to put the rad cap on and the end bit lifting against system pressure that uncovers the expansion tank port bleeding coolant pressure off, sure you know this already but just to be clear what we're talking about. They also tend to loose the rubber bit on the radiator cap itself that pushes on the cap neck sealing area and then they don't seal anyway.
If you scuff up the top of the rad cap so you can read it, they usually state the pressure they lift at on them. Mine had a 12psi cap when I got it, which physically fitted, but is too high. Maddening because it has to be one of the cheapest things to get the right replacement one of on the whole machine.

[CHRISEEBOY]

Cheers MrF, that's really useful. I will have another look over the weekend.

[Matchless?58]

Really comprehensive and useful information Mr f . Thanks for posting . Just at the right time for me as I'm about to tackle the water pump issue I've had for a while on my 3c11 . My rad cap don't fit properly either so as I've got to remove the rad anyway I'm going to take the opportunity to give it a good clean and hopefully sort out the cap at the same time . I was completely unaware it should have an expansion bottle as mine is missing but it does make sense . I don't think it will be too difficult to make something up to replace the missing bottle . I have a scrap mercedes Vito sitting in the yard so I might try to rob the bottle off that .
Cheers Chris

[CHRISEEBOY]

Looks like it is a pressure release cap. From what I can make out its says "remove slowly" then and up arrow, then 0.9.

Presumably it releases the pressure ate 0.9 PSI? That sounds a bit low?

Do I need to rig up my own expension bottle or can I just do without it and make sure I always keep the rad full? If I install an expansion bottle, where does the coolant go that gets trapped in the bottle?

[MrF]

I would invest in a new cap myself, they're not expensive & I dont think that stands much chance of sealing well unless it looks rougher in a photo than it is. 0.9bar is 13psi, so that's a more likely figure. The seat the bottom pushes onto also needs to be flat for it to seal well along with the top of the neck for the secondary seal.

For the expansion tank, it has to go on the hole in the radiator neck not in a pressurised part of the system, so when the cap releases pressure, it vents into the expansion tank via that little hole. Then when the motor cools down after being switched off, the coolant contracts, and it gets drawn back into the system from the tank because the connection from the radiator in the expansion tank is under the fluid level & the other port on the tank is open to atmosphere.
Its not that important if you just keep a eye on the fluid level at the start of the days work as your a bit stuffed as the barb it connects to on the neck is snapped off.

Random internet link explaining the two systems inside a radiator pressure cap, they're quite complex for what looks at first glance to just be a way to block a hole off :- https://championcooling.wordpress.com/2 ... e-ratings/