N o Heat

[youngman]

I Have a 2000 S 3.0 type Jaguar and the heat is not working.The coolant level is ok.The Fan is working fine.I changed the thermastate.I check the heat switch it's ok.The heater core isn't leaking.The core hoses might be glod but I cant get to them.Please Please help me.

[Paul22118]

I had a similar problem with another make of car years ago. I tried everything known to man until an old mechanic who worked in a country garage in Wales said to me what he thought would solve it.

The problem was an air lock. You cannot see the air lock and it can be as obstructive as a lump of clay in the system. He emptied the system when cold. This ensured the stat was shut. Fill the system with cap off and run until the temp gets to a point that the stat opens. Then top up with boiling water and squeeze the hose pipes and create squelching noises. When boiling water gets to top of neck put cap on and run till guage shows normal. Let cool naturally and when cold open cap and top up cold if required. Tighten cap and run. That sorted the problem.

[Tim B]

The easiest answer is that there is a blockage. The blockage could be physical or it could be an air lock. It's just possible that someone has put a "Radweld" type product into your system which has blocked it. In this case you need to get the engine up to temperature, disconnect the lowermost hose, connect a water main hose to one of the exposed pipe ends and "back flush" the system with the engine running.

You need to do pretty much the same if the problem is an airlock. The t'stat needs to be open (engine at normal temp.) because the air might be trapped against it. The air needs to rise to the top of the system, so I would say, again, disconnect a hose at the bottom of the system and with the engine running gently insert water from a mains hose at this point. Have the engine running, you may have to encourage air to move at the top of the system by squeezing the hoses but being a Jaguar you might have bleed valves to let the air out.

Best bet is to buy a Haynes manual for your car.

Good luck.

[Pheasant]

I don't know about modern Jags but most older ones heaters operated on a vacuum system Basically when you operated the heater control in the car it opened an air valve that allowed a vacuum from the inlet manifold to suck open the air duct in front of the heater matrix. This air duct would open by degrees, depending on the strength of the vacuum, which in turn depended on how hot your heater control knob was set at. If any of the vacuum pipes in the system were perforated or perished then the system would fail as there would not be enough suction to open the air duct.

This air duct is essential. If it is not opening then no matter how hot your heater matrix gets you will only get an icy blast. It sits below the grille in front of the windscreen, through which it draws air. If it is stuck in the "Cold" position then it just sends air from outside straight into the car. When it moves to the "Hot" position it ducts the air through the heater matrix first and then into the car. If it is possible, remove the air intake grille and get someone to turn the heater control up and down and see in the flap moves. If it doesn't, as a temporary measure you could try wedging it into a position where it ducts the air over the heater matrix.

You may also find that it could be a fuse or relay failure. Although Jags have long had Fuse Failure messages come up on the dash this only applies to certain crucial circuits such as lights etc. The air intake duct may well now be operated by motors these days. A relevant fuse may have blown, but you'll probably have to check each one individually as it is unlikely to list the air intake duct in the lid of the fuse box, it may well be part of another circuit. Similarly a relay may have blown.

Before going too wild checking for airlocks see if you can trace the two heater hoses that go to the matrix. If there is an airlock then the one going in will be hot, the one coming out will be cold.