If the fluid is just water, the likely source is a blocked A/C evaporator drain.  In this case, it is (usually) simply a matter of sliding underneath the car and squeezing the ends of the drains which come through the floor either side of the front of the transmission. This will release the muck that blocks the ends of the hoses and you will be greeted with a flow of water all over your arm. In severe cases, you may have to slide a flexible prod (perhaps an old speedo cable) up the drain to loosen any accumulated muck.

Air Con drain plug. Squeeze this to release the trapped water (one each side of the transmission)

However, in the event that the heater O-rings are leaking, you have a much bigger job on your hands. A loss of coolant without any obvious leaks in the visible engine bay hoses, radiator or water pump is another symptom -- in my case this is how I noticed the problem before it progressed to the stage where the footwell became badly soaked with coolant. At about 130,000 miles I had an inexplicable slow coolant loss from the reservoir and sure enough, the leak  was traced to the heater core O-rings.

The heater O-rings seal the aluminium pipes that connect the heater to the engine bay (see diagram below). The pipes protrude through the firewall on the right-hand side (viewed from the driver's seat). We suspect that if you disturb these pipes during replacement of the heater hoses, the O-ring sealing may be compromised - especially as the O-rings, when removed, have been found to be hard and cracked.

Heater Assembly Reference Diagram (adapted from shop manual) showing heater hoses connected to the heater matrix core.	Closeup Drawing (adapted from shop manual) of highlighted area in drawing at left, showing the water pipes and the heater O-rings. (As an aside, the Core Temperature Sensor clips onto the lower pipe 6).

Shortcuts to O-Ring Replacement Procedure

The official O-ring replacement procedure outlined in the shop manual is to devote 12 hours of labor (by you or the dealer) to removing the entire dashboard and center console, disconnecting the air conditioning, disconnecting both airbags, and pulling the steering column. While this procedure is necessary when the entire heater core needs replacing, alert readers have found shortcuts which greatly ease the pain of the operation and avoid massive dismantling of the dash.

As the heater O-ring connection is under the right-hand side of the dash, it is a fairly inconvenient fix for RHD vehicles owing to the steering column and other stuff under the dash. For LHD vehicle owners, it is easier (see below) as there is only the glove box and transmission hump side panel to remove. Ron Beckett of Australia has supplied the following details on how to replace the O-rings in a RHD Australian 4.6, after he noticed a bit of leakage onto the carpet, apparently triggered by  disturbing the fittings whilst replacing all the water hoses. We are also extremely grateful to David Sparkes in the UK for the initial advice, especially where to drill holes, and photos (not reproduced here) on how to remove the ducting in order to access the blend motors (another page in preparation!). Note that the basics of replacement don't change for a LHD car, it's just that you may have more access for your hands - which makes it easier.

An alternative method of accessing the O-rings is removing the dash -- this operation is described on the Dashboard Removal Page.

Once you have everything apart, Ron also highly recommends you replace the Core Temperature Sensor at the same time. The sensor clips onto the lower heater pipe and is very easy replace whilst you have the car apart. It is a common failure item and if you have the TestBook symbol appearing on the HEVAC display, followed by it having cleared at next start up, there is every chance the sensor has failed. It's not cheap (about US$30, A$50) but it's probably still worth doing. It probably also affects the operation of the air conditioning as it provides information about the water temperature to the HEVAC system - so it's better that it works properly.

O-Ring Location and Access

The O-rings are located on the right hand side and above the transmission hump - actually just above the RH footwell air vent. In fact, if the O-rings are leaking, you often find tell-tale white residue from the coolant in, or around, the vent - see photo below. To get access to the O-ring connection requires that you will have to remove the large lower fascia under the steering column (RHD vehicles), and the RH side panel on the centre console. Ideally, you need to remove the instrument panel as well to gain access to the upper end of the ducting. The workshop manual tells you to remove the complete fascia (dash) assembly - officially a 12 hour job but reduced to 6 hours (including removal and replacement) using the procedures described on the Dashboard Removal Page. Thus, the method to be described below is much quicker. A lot of this work is also required if you need to replace the distribution or blend flap motors (see blend motor replacement page) - another job which LR say requires removal of the fascia assembly.  

Start by removing the RH side panel - see the page on Removal and Replacement of the Side Panels.

With the side cover off, you now have access to the lower air vent and duct. The outer vent outlet just pulls off. The inner vent outlet is retained by two screws, one of which also holds the air duct in place. Remove these two screws.  Note the white residue on the heater matrix above the vent where the coolant has flowed down. Unfortunately, the residue on the vent itself had been cleaned off before the photo was taken. 

Above: Pull off the outer vent and ...	Above: Remove the two inner vent retaining screws.

The air duct which runs from the screen down to the floor is further retained by a screw hidden behind an inner panel. You have two options: (a) pull on the duct to break off the mounting lug or (b) drill a hole through the inner panel to access the screw. This hole will be covered when you refit the side finishing panel removed earlier. The photo below shows where to drill the hole to access the hidden screw. 

Above: Drill a hole here to access the hidden screw behind...	Above: Stay Tuned!

At this point, the access procedures diverge for the LHD and RHD vehicles - but this section deals with the additional access for RHD vehicles. In this case we need to release the top of the duct to allow it pivot out of the way at the bottom. (This will become clear when you do the job). To do this we have to remove the instrument panel. It may not be strictly necessary to do this but I didn't feel comfortable with flexing the lower heater duct out of the way to get to the O-ring heater connection screw.

So for RHD vehicle owners, we refer you to the instrument binnacle removal page - see Removal and Replacement of Instrument Panel

Removal of the Heater Ducts

Removal

After pulling out the instrument panel, you will now be able to access the top of the heater ducts. These ducts connect the heater to the upper outer dash vents and to the floor vents.

Referring to the pictures below, slide the intermediate joiner to the right to disconnect the inner duct from the outer duct. This will allow the inner duct to be separated from the heater and swung away at the lower end near the heater matrix. It will require quite some flexing of the duct to get it out of the way - but it can take it the flexing.

Above: Slide this intermediate joining piece right to....	Above: .... disconnect the inner and out ducts.

Optional Access Improvement Surgery

Kevin Potter of New Zealand found that after removing the instrument cluster and pushing forward the heater ducting as per the above instructions, it was advantageous to bore a hole in the inner right hand panel, using a hole saw (see picture below). This allowed him to get a long 250mm phillips head screwdriver (without handle) in to  release the o-ring clamp (see below). Using this technique, he reports that removal and replacement was quite easy, saving  quite a bit of time (total time including repair of broken fittings  from previous morons 6 hours - should have been 3!!)

Kevin's innovative method for easing access to the screw securing the heater pipe clamp (see next step). Cutting a hole in the inner side panel also allows you to see what you are doing,, and does not significantly affect its structural integrity.

Removal and Replacing of the O-rings

Removal   

Above: Pipe connector to heater matrix. Below: The pipe clamp released. You can just make out the edge of the O-ring on the lower pipe.	Above: Another view of the heater pipe attachment. Note just-visible phillips head screw which has to be removed to release the pipe clamp (see below left). That blue item is the connector to the heater core temperature sensor which is clipped over the heater pipes and which often fails. Below: Heater core temperature sensor mentioned above.

Abbreviated Procedure for Left-Hand Drive Models

 Thomas Dirksen found a much faster way to replace the O-rings when coolant started leaking into the cabin of his US-spec 4.6 HSE, saving $1,000 in labor. He removed the glove box and was able to loosen the screw holding the O-rings by going through the glove box lock hole. This procedure took about 3 hours.

Thomas bought two O-rings from the dealer for $10. Then he removed the glove box and panels and the glove box lock. Looking inside the lock hole you can see the single screw that secures the O-rings. He used about 16" worth of 1/4" drive extensions, with a universal joint, to reach the philips screw. He secured the bit and the socket with 3M high strength adhesive so they would not fall off while trying to loosen the screw.  Once the screw is loosened the heater pipes disconnected very easily and were very accessible where the glove box was removed.

To install the new parts, he cleaned the crust off the pipes where the coolant had been leaking, and lubed the O-rings with coolant. The philips screw was damaged during removal, so he replaced it with a hex drive machine bolt of the same thread pattern, complete with locking and flat washers. He used the 3M high strength adhesive to temporarily bond the new screw to a hex drive bit. He managed to insert the screw into the hole, and when it was sticking out on the other side by 1/8" he placed a drop of Loctite on the exposed threads. He pushed the O-ring fastening bracket on to the bolt and tightened the bolt down all the way. The leak was gone!!!

Simon Goode confirms the effectiveness of this technique. The only snag he struck was: "When trying to undo the screw I rounded it out and had to end up cutting a slot in it with a hacksaw blade to fit a blade head driver in. Then when I attempted to undo it the screw snapped. I then had to remove the pipes and plate to drill out the broken screw.  That worked and it all went back together! I managed all this with only removing the parts described in your page. So just to let others know even when it does not all go to plan you do not need to remove all the dash!"

Lonn Howard also used this method: "I changed my matrix o-rings by passing the socket extension through the glove box lock hole.... the extension was guided as if by magic to the cap screw almost every time. (The dealer) had never tried it that way, preferring instead to go through the space vacated by the radio. A word to the wise... refill with water only to test your connection."

Footnote: The official Land Rover dealers may now be cottoning on to this faster procedure pioneered by Thomas. The local dealer recently replaced my heater core O-rings (April 2003) and I was only charged for about 4 hours of labor.

Even Faster Method for Left Hand Drive Vehicles

Update February 2008: A Land Rover tech of 10 years standing alerted us that there is now a much easier way the dealers have figured out. "All you need to do is pull the glove box and the hvac unit. You can slide a very long posidrive screwdriver through the upper right corner of the hvac unit mounting opening all the way back into the screw that secures the heater pipes into the heater box. I have done countless of these repairs while working at the dealer for ten years. You can figure on spending about and hour and a half the first time, after that you can start getting them done in 45 minutes or so".

If by chance you happen to strip out the screw for the heater core o-rings most of the time you can apply a small amount of valve grinding compound to the screwdriver head and get enough grip to break the screw loose.

Replacing the Heater Core

Thomas Dirksen who pioneered the abbreviated O-ring procedure described above for LHD models, recently had occasion to change the entire heater core. The O-rings lasted for about 60K miles, and then started leaking again. However, this time he noticed that the head on the heater core showed a hairline crack, dictating  that the entire heater core had to be removed and replaced. Thomas thinks that although it was probably weakened from heat cycling and old age, he may have cracked may have cracked it when I yanking too hard on the heater hoses when he changed them. (Something to think about. Prolly a good idea to go easy when changing heater hoses.

Officially, replacing the heater core requires the removal of the entire dash/fascia. However once again., Thomas found a shortcut method that makes this operation much more bearable.

"After removing the glovebox, I drilled through various spot welds on the dashboard frame. Then I partially sawcut an ell bracked and gently bent it out of the way to remove the heater core. I then lapped to pieces of metal and riveted the frame back together, and then riveted the spot welds I previously driller. So it is possible to change a p38 heater core without removing the dash fascia."

Parts Required:

Above: The tools required for the job. Note the flexible bit-driver. Below: I replaced the phillips head screw with a socket head cap screw cut to the right length, hence the need for the allen key drive bit.

More Information

Dash Removal Method:  Jos Geuze removed his dash (fascia), which is the O-ring access method recommended in the shop manual. He found this is not as difficult an operation as previously thought, and has provided a full illustrated description on the dash removal page.

Andy Cunningham has a text-only description of David Allcock's approach for the UK-spec 4.0/4.6, with alternatives by David Sparkes, at this link.