Coolant Problems

[funbus1]

Hi, still havent fitted my new expansion tank yet, because im a bit conc erned about the smaller hole at the top, If i reduce the hose to fit the tank, will this reduce the flow and cause overheating problems?? Also is the top one the inlet or outlet/? Help please.. Im sick sitting in him and not driving.

[mirams]

Top pipe is the inlet, bottom the outlet. The reduced size will just cause increased pressure and higher speed flow over such a short stretch - it will just squirt the same amount of coolant in, in a faster thinner jet.

[funbus1]

Hi Mirams, Let me know what tank you get, i think theres 2 different ones,let me know how you get on, cheers.

[Whitevanman]

The main expansion tank keeps overflowing onto the exhaust and on investigation there is a 10mm hole in the top of it. This means the main expansion tank is not pressurised so water is not transferred to the top up tank when hot but overflows instead.

I don't know what the hole is for as all pipes are connected. I can ony assume it once contained a pressure relif valve that has blown out (perhaps because the valve in the cap is blocked).

Any help appreciated

Mark

[Westy.Club.Joker]

The top tank with the blue cap is the pressure tank. The one behind the flap is an expansion tank, which is un-pressurised.

When the engine heats up, the water in the system will expand and the pressure inscreases. At around 1bar (14psi) the valve in the blue cap will release pressure and allow any water to flow to the expansion tank, which being open to atmosphere will allow this. The blue pressure cap holds the engine water pressure at 1 bar which is normal running pressure and temperature. If the engine gets a bit hot, hard running up hill etc, it will allow a bit more coolant out and into the expansion tank.

When you park up and the engine cools down, the engine coolant cools and contracts, so there is a pressure drop in the main header (pressure) tank, the valve in the blue cap will open, as the cooling effect makes the pressure drop, and this then "sucks" coolant BACK INTO the header tank FROM the expansion tank (behind the flap) so your top tank should always be full, hot or cold.

If it isn`t allowing coolant BACK when cold, then either the tank cap is knacked (stuck valve) or the pressure isn`t dropping in the system when it`s cold, which indicates a cylinder head or gasket problem, it`s possible that a head or gasket problem allows the system to pressurise when it`s running and will send coolant from the pressure tank to the expansion tank, but HOLDS the pressure in the system when it goes cold which doesn`t allow the coolant to return from the expansion tank into the top pressure tank. So your top header tank level drops and never re-fills.

I know this to be true because mine does it The engine runs fine, just has the coolant level dropping problem. I`m swapping the engine for a known good one in a couple of weeks.

[Whitevanman]

Thanks for clarifying the terminology. The problem I have is that the top tank (pressurised with the blue top) has a 10mm hole in it so it can't overflow / suck back from/to the overflow tank. I don't understand why the hole is there. My only explanation is that it is a relif valve that has blown out to save a hose / gasket.

Thanks

Mark

[Whitevanman]

OK, the 10mm hole is probably a unique modification to my van. The previous owner had ingeniously? fitted a tyre valve to the expansion tank to relieve pressure build up because of a leaking head gasket. Rather inconvenient having to open the engine cover after each run but effective non the less! The head gasket has been fixed but eventually the now redundant valve blew out and caused the cooling system to overflow. Fixed with a bolt with a couple of large washers and some Araldite. Probably a red herring in terms of regular problems but thanks for everyone's input.

[mirams]

Hello,

I got a new expansion tank (inc. cap) and level sensor from local VW commercial branch. £40 altogether, which is similar to JK prices, so pretty good I thought.

Got off old expansion tank and there was a crack just under the seam, which only opened under high pressure.

New tank fitted without any problems, first time I hadn't tightened everything up quite enough so excess coolant went into top-up tank, but air was sucked in as pressure dropped. Level sensor caused dashboard to flash (which has never happened before - well worth a new one of them (£10) , plus old one might not seal properly). I tightened the sensor and pipe onto pressure cap and it now works perfectly again.

Thanks for all your suggestions.