Thread: Leaking heater box

So, it's correct to deduce that you can't remove the heater matrix without removing the whole heater box?

Originally Posted by Ranga

So, it's correct to deduce that you can't remove the heater matrix without removing the whole heater box?

Probably like you , started loosing coolant , then the tell tell signs water stains under the hearer box . First thing I did was plug the hoses off . My thought's were just take the screws out of to top of the heater box and slip it out . Soon found out you can't do that , The heater box does have to come out . That got me scratching my head . You need long socket extention to reach the fixing bolts , the problem is you need to hold the nuts in the foot well ,or they spin . Once you get them out the other bits are not to bad , the inlet easy . The core in mine is made out of aluminum and plastic , that's the old one , and the new one . One other tip make sire you put the protective packing back in or even replace It . Without that I would think vibration would soon damage the new core . Jim

IF you can get one the older county and series ones hold up better.

while you have the box apart find and gut a 12v heater mount the electric element in the cabin side of the ducting wire it up on a relay that also connects to the low speed fan setting so if you turn the elec heater on the fan also comes on on low speed.

on those really cold mornings its not enough to heat the cab but it will demist and de ice the windshield. as I have a permanent Dual battery setup Mines powered off the Aux battery so I can turn it on without worrying about the main battery while the engines not running.

Originally Posted by jimr1

Hi Andrew , like you when mine went I bypassed It . My fix was I had a bit of dowl about 18mm dia . so I cut two bits about 50mm long plugged the hoses , put two hose clamps on . Tha fixed It till I got a new core !!.. Jim

Seems to me this should be used just for short term fix, not longer term in hot and heavy load conditions. With this heater turned off, water still should flow through the element. Note how reported damage to 300Tdi's from overheating seems to occur first around No 4 cylinder. Not a good idea to reduce or stop coolant flow there. Water obviously would not circulate past it as much in the head with heater circuit blocked off with these plugs. Would also be slowed by partially blocked element. So the solution as proposed by 86mud is preferable. Or as I had when heater was removed, one piece of three quarter inch standard heater hose connected to the fitting on the head, doing three quarters of a loop and the other end connected to the return pipe.


Effectively same result but probably easier to obtain bits to achieve it than 86mud used. No need to wrap tape around fitting in head of mine. Standard 5/8"" diameter to fit into special hose and with 3/8" BSP thread had earlier been replaced with more sensible standard one which fits 3/4" hose. The outlet hole in cylinder head has been bored and tapped to take 1/2" BSP. (Note that British Standard Pipe sizes are the approximate diameters of the pipe bores. Diameters of where threads are is much larger and these are the measurements that are critical.)

Originally Posted by mox

Seems to me this should be used just for short term fix, not longer term in hot and heavy load conditions. With this heater turned off, water still should flow through the element. Note how reported damage to 300Tdi's from overheating seems to occur first around No 4 cylinder. Not a good idea to reduce or stop coolant flow there. Water obviously would not circulate past it as much in the head with heater circuit blocked off with these plugs. Would also be slowed by partially blocked element. So the solution as proposed by 86mud is preferable. Or as I had when heater was removed, one piece of three quarter inch standard heater hose connected to the fitting on the head, doing three quarters of a loop and the other end connected to the return pipe.


Effectively same result but probably easier to obtain bits to achieve it than 86mud used. No need to wrap tape around fitting in head of mine. Standard 5/8"" diameter to fit into special hose and with 3/8" BSP thread had earlier been replaced with more sensible standard one which fits 3/4" hose. The outlet hole in cylinder head has been bored and tapped to take 1/2" BSP. (Note that British Standard Pipe sizes are the approximate diameters of the pipe bores. Diameters of where threads are is much larger and these are the measurements that are critical.)

If you read what I said , It was a temporary fix ,until I got a new heating core , two day's later . This fix is only a temporary bush fix It would get you home . My truck is a td5 , there is a lot of plumbing on them . I don't think they rely on the heater core as part of the cooling system , plus Melbourne is not Tropical . I suppose if your heater goes , when out back and you have all these bit to do a repair , that's great !!..

Originally Posted by Blknight.aus

IF you can get one the older county and series ones hold up better.

while you have the box apart find and gut a 12v heater mount the electric element in the cabin side of the ducting wire it up on a relay that also connects to the low speed fan setting so if you turn the elec heater on the fan also comes on on low speed.

on those really cold mornings its not enough to heat the cab but it will demist and de ice the windshield. as I have a permanent Dual battery setup Mines powered off the Aux battery so I can turn it on without worrying about the main battery while the engines not running.

Where would one find one of these 12v heaters?

inside the heater box of any defender, county or D1 I've done alpine prep on.



probably of more use would be the 12v shop, ebay, jaycar and specialist RV shops.

the last ones I got were from bay $6 each but they were advertised as 12v hair riers. the wre a perfect fit into duct that directs air up to the demist of the windhsield.

Originally Posted by Blknight.aus

inside the heater box of any defender, county or D1 I've done alpine prep on.



probably of more use would be the 12v shop, ebay, jaycar and specialist RV shops.

the last ones I got were from bay $6 each but they were advertised as 12v hair riers. the wre a perfect fit into duct that directs air up to the demist of the windhsield.

Running them for prolonged periods doesn't burn them out?