P38 Heater Core O-Ring Replacement


Introduction: Wet Carpet Symptoms and Causes
Shortcuts to O-Ring Replacement Procedure
O-Ring Location
Removal and Replacement of the Heater Ducting
Optional "Access Improvement Surgery"
Removal and Replacement of the O-rings
Abbreviated Procedure for LHD Models
Even Faster Method for LHD Models
Replacing the Entire Heater Core
Parts Required
Tools
More Information


Special thanks to Ron Beckett for going above and beyond the call of duty to produce this page!

Introduction: Wet Carpet Symptoms and Causes
A number of owners have noticed the front carpets in their P38 Range Rovers becoming wet. It is important not to panic when this happens; it does not necessarily mean the heater matrix has failed (aqs was notoriously the case on the Classic)! Much more likely, it is simply a matter of either blocked air conditioning drains or that the heater O-rings need replacing.  The O-rings are located inside the passenger compartment under the right hand side of the dash, so if you notice fluid in the right hand footwell but not the left one, this is a very likely cause.

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.

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.

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 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. 

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. 

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.

Removal and Replacing of the O-rings

Removal   

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 catching 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
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
If the O-ring replacement does not fix the leak and you need to replace the entire heater core, Rangerovers.net enthusiasts have found shoetcuts to this procedure too -- it really isn't so bad!! FOr full details of this operation see the 4.0/4.6 Heater Core Replacement Page.

Parts Required:

O-Ring Replacement:
2 heater core O-rings, part number STC 3262.

Heater Core Replacement:
Sources for new heater cores are detailed at http://rangerovers.net/rrparts4.html#climate

Tools Used