blocked heater matrix XJ series 3 3.4

[CliveRothwell]

Both the inlet and the outlet pipes are hot to touch suggesting flow through the matrix. However, whilst, unusually, all flaps work using vacuum, only really weak cool air is produced even when asking for heat. The matrix was a new unit fitted some 7 years ago before a cylinder head refurb job. Any thoughts / remedies / old wives tales please?

[stevewarbs]

I would expect the outlet to be appreciably cooler than the inlet as the the heat is lost through the matrix. If the outlet is the same temp then that could be that wither the matrix is blocked and the coolant is mostly bypassing it or there could be an airlock in the matrix.

The other thing you could check is that the air inlet flap in the scuttle panel is opening. I recently had a split vacuum hose which meant it didn't open and I had no warm air to the car.

Good luck
Steve

[CliveRothwell]

That sounds like a good idea to me Steve, many thanks. I'll investigate further along those lines.

[PaulGover]

If you suspect a blocked radiator, and you have an appropriate specialist nearby (in the good old days, look in Yellow Pages), the easiest thing to do is whip it out and let them refurbish it. When I last did it (admittedly some years ago) the cost was relatively low (much less than a new radiator) and the result much better than chemicals (he'd unsoldered the end caps, rodded through pipes, repaired leaks and tidied the fins).

If you prefer the chemical route, if you can find the two pack Holts one, or use 1/5th of a tub of Fernox central heating descaler (the powder version, not the liquid; as far as I could see, it's the same stuff as Holts, I believe malic acid crystals). It's particularly good at clearing the rusty build-up that the XK engine block is notorious for. One downside: if your core plugs have deteriorated, you'll find out 'cos they'll leak like a sieve after it's dissolved the rust blocking the holes!

[oldtimer]

Hi Clive,
Sounds very much like my 'ole '73 Series Two. Inlet and Outlet pipes get nice and hot, switch the fan on and some heat for a few moment then goes cold. To me, a sure sign of a blocked heater matrix,
I've had a replacement matrix on the shelf for years ! Procrastination rules OK.
-
Bit surprised that this has returned after 7 years - any idea as to the state of the rest of the cooling system, has corrosion and crud accumulations managed to congregate in the Matrix ?

Has the cooling system always been filled with Ethyl Glycol anti freeze with anti corrosion inhibitor package all year round to the industry standard 50/50 mix

[CliveRothwell]

I'm beginning to suspect a blocked matrix from what you have been saying. Whilst the matrix is just 7 years old, it was fitted into an old system. 3 years ago, the head was done along with a new - yes new radiator with new core plugs as well. If I'm ever allowed out to play with the car ever again, I'll have a go at isolating the inlet / outlet pipes, letting the matrix stand with Holts rad cleaner and then carefully put the power washer through the matrix.

Thanks for the advice all of you.

[J44EAG]

I clean out marine heat exchangers with brick acid or caustic soda. Tough jobs need tough chemicals.

At the risk of being shot out of the water, pulling off the bottom hose, draining the rad and plugging with a bung of some kind, I would then be filling the rad with some of the above and let stand for a few hours. I`d expect that a fair amount of detriatus to be washer out during a good flush out. The rad could stay in the car but care will be needed to avoid splashes from any evil chemical used.

Mike K

[CliveRothwell]

Mike - that also sounds like a cunning plan that could be well worth a try before the car gets it's paint job early next year. Many thanks indeed.