Range Rover P38 Cooling System Troubleshooting Update – BMW M51

Over the past weekend, I finally managed to find some time to take a deeper look at the P38. The goal was to pinpoint the exact cause of the issue — whether it was a failing head gasket or something else entirely.

To eliminate the possibility of air being drawn into the cooling system through a leaking radiator or degraded hoses, I decided to proactively replace several key components.

I replaced:

• The radiator

• The bypass hose at the rear of the engine

• The hose between the thermostat housing and the heater core

• The thermostat O-ring

• The water pump

The radiator was already on my replacement list. I opted for a thicker aluminum performance radiator, which offers increased cooling capacity compared to the original unit. This upgrade not only improves heat dissipation but also helps rule out radiator-related issues during troubleshooting.

By replacing these components, I could confidently exclude common failure points in the BMW M51 cooling system and focus further diagnostics on the root cause of the problem.

Link to Direnza radiator:
P38 DSE Direnza Aluminum Radiator

P38 diesel Direnza performance radiator

Cooling System Pressure Test Results – Range Rover P38 BMW M51

To further diagnose the issue, I performed a cooling system pressure test. Starting at 15 psi, the system consistently lost around 2.5 psi within a few minutes. In my view, that’s still problematic and indicates that something isn’t right.

While the system was under pressure, I carefully inspected all hoses and connections for visible coolant leaks. No external leaks were found. I also checked the heater core area, but since the heater matrix had already been replaced and is fitted with relatively new O-rings, the likelihood of a leak there was minimal.

With no external leaks present, this strongly suggests an internal issue.

At this point, the only remaining logical conclusion is that the cylinder head will need to come off for further inspection and replacement.

More on this soon 👊

Range Rover P38 Cooling System Problems – From Road Trip to Head Gasket Failure

It might not come as a surprise, but at the moment the P38 isn’t running particularly well.

That said, I did drive it last summer — well, towards the end of summer — all the way to the Alps. I couldn’t use it earlier in the season because the transfer case and torque converter still needed to be replaced. Once that work was done, I decided to take it on a proper test: a 2,500 km round trip.

Apart from some overheating brakes, the journey was completely uneventful. That trip finally cured me of the infamous “P38 paranoia” and gave me the confidence that I could just hop in and go anywhere.

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When Things Went Wrong

That confidence lasted right up until a trip to the Belgian Ardennes.

Halfway down the motorway, I suddenly saw steam coming from both the front and the rear of the car. With my heart in my throat, I was luckily able to pull off at a nearby petrol station.

There, I discovered that the top right radiator hose had come off, dumping all the coolant. I took a moment to regroup, grabbed my tools, bought several bottles of water, refilled the system, and carefully drove home at a very conservative pace.

Once home, I parked the car and wanted absolutely nothing to do with it. I was completely gutted.

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Initial Diagnosis

About a week later, I started looking into the problem more seriously. I ordered a combustion leak tester and fluid to check for a possible head gasket failure. The fluid did turn yellow — although it took quite some time, which already raised some questions.

To better observe what was going on, I installed a transparent hose between the top of the radiator and the expansion tank. This allowed me to visually monitor the coolant flow. I noticed bubbles in the line — sometimes steady, sometimes none at all.

The cooling hoses also became slightly stiffer once the system was closed and pressurized. That in itself isn’t abnormal, as long as they don’t become rock-hard.

I then used an Amazon pressure tester and confirmed that the system was losing pressure. Unfortunately, at that stage, I still couldn’t pinpoint exactly where.

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Parts Replacement & Escalation

At that point, I started sourcing parts to eliminate potential failure points. I ordered:

• A new water pump

• Thermostat O-ring

• Bypass pipe behind the engine

• An aluminum radiator

• A head gasket

• New head bolts

• Additional gaskets

With the BMW M51 diesel, things get tricky. Once the cylinder head is warped, skimming is not recommended, as it can lead to cracks around the swirl chambers.

I always believed new cylinder heads were essentially unobtainable — until I discovered that AMC had just produced a new batch. I didn’t hesitate and ordered one immediately. Even if it turns out not to be strictly necessary, I’m happy to have one available just in case.

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Looking Back

If you’ve been following the blog for a while, you may remember that I overhauled the engine about two years ago. At the time, I inspected the cylinder head and already knew it wasn’t fully within specification for longitudinal flatness. If memory serves me right, the limit is 0.10 mm — and mine measured somewhere between 0.10 and 0.15 mm.

According to RAVE, these heads should not be skimmed, so back then I decided to take a calculated risk and reinstall it anyway. That gamble paid off — at least until now.

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What’s Next

At this point, I have nearly all the required parts on hand. I’ll continue troubleshooting for a bit longer before fully committing to removing and replacing the cylinder head.

More to come.

By the way some pictures for your enjoyment ✋

Range Rover P38 EAS FAS Kit – Manual Air Suspension Backup Explained

Some time ago, I purchased a so-called FAS kit from a Spanish company.

This system allows you to continue using the Electronic Air Suspension (EAS) even in the event of a failure of certain EAS components, including:

• The compressor

• Height sensors

• Valve block

• EAS ECU

• Timer relay

The main goal of the kit is to allow manual control of the air suspension by supplying air directly to the individual air springs or the air tank using an external compressor.

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How the FAS Kit Works

The kit consists of five Schrader valves, which means the system can even be operated using a simple hand pump or foot pump if needed. This makes it an extremely practical solution when travelling off-grid or in remote locations.

In my case, the air suspension has been fully rebuilt and is currently working perfectly. However, when venturing further away from civilization, this setup provides an extra safety net — a way to keep moving even if the factory EAS electronics decide to call it a day.

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Limitations

Of course, if an air spring itself ruptures, the trip is over regardless. That’s the one failure scenario this system cannot mitigate.

That said, since my suspension airbags are new, I don’t expect any issues anytime soon.

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Final Thoughts

For anyone running a Range Rover P38 with EAS and planning remote travel, a FAS kit is a smart addition. It doesn’t replace proper maintenance, but it does provide peace of mind — and sometimes, that’s exactly what keeps an adventure going.

Installing a Larger Volume Intercooler on the Range Rover P38 (BMW M51)

It took a while, but I finally got around to installing a larger volume intercooler on the Range Rover P38.

I ordered the unit as a Britpart replacement, although it appears the actual manufacturer is Serck Motorsport.

When the intercooler arrived, the weather was poor and I was short on time — which, in hindsight, wasn’t ideal. As expected, the installation turned out to be anything but straightforward, especially when done in a hurry.

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Preparation and Removal

For easier access, I decided to drain the cooling system, which is highly recommended for this job. While doing so, I also removed the right-hand radiator support bracket that bolts to the chassis. This creates much-needed space to manoeuvre the intercooler into position.

Because this upgraded intercooler is thicker and shaped differently compared to the OEM unit, the original mounting points cannot be reused. On top of that, the fit is extremely tight.

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Intercooler and Oil Cooler Installation

Once the intercooler was positioned, I reinstalled the radiator. Due to the increased thickness of the intercooler, the engine oil cooler now has to be mounted above the intercooler instead of below it.

With everything loosely in place, I marked the mounting points and drilled new holes in the side support pillars to secure both the intercooler and the oil cooler. To improve clearance, I added a 3 mm thick washer behind the intercooler.

The vertical position of the intercooler is largely dictated by the oil cooler, as it sits just below the top of the radiator. Positioned this way, the intercooler hoses line up properly with both the turbo outlet and the intake piping. One important thing to watch out for is clearance on the left-hand side near the washer bottle filler neck.

For now, I used self-tapping screws to secure everything. I may replace these with proper bolts and nuts at a later stage.

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Results and Driving Impressions

So, does it make a difference?

First of all, I discovered that the old intercooler was leaking, which meant I was losing boost pressure. That alone justified the upgrade.

I haven’t driven the car extensively yet, as the transfer case still needs attention. However, even from limited driving, the engine feels stronger at lower RPM, and throttle response seems improved.

I also noticed that the engine is running cooler. That said, I did clean the radiator while the coolant was drained, so that likely contributed as well.

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Final Thoughts

Overall, I’m very happy with the result. Once the drivetrain issues are sorted, I may experiment with a slight increase in boost pressure to extract a bit more power — nothing extreme.

But first things first:
the transfer case, ball joints, and panhard rod bushes 😏😐😂
That’s a job for another time.

Choosing the Right Tyres for a Range Rover P38: Why I Went with 265/70 R16

For quite some time, I’ve been looking for tyres that offer better off-road performance for the Range Rover P38, without committing to a full mud-terrain setup.

In my use case, mud-terrain tyres would only see limited off-road mileage. That makes them noisy, heavy and unnecessary for everyday driving. Instead, I was looking for a tyre that sits between an all-terrain and a mud-terrain: aggressive enough off-road, yet still civilised and predictable on the road.

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Initial Tyre Options Considered

My first shortlist included several well-known and proven options:

• Falken Wildpeak AT3

• Toyo Open Country AT3

• Kumho Road Venture MT51

On paper, all of these tyres are solid choices for mixed on- and off-road use. The real limitation, however, turned out to be availability and correct sizing. Either the tyres were not available at all, or not offered in the specific size I was targeting for the P38.

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Why 265/70 R16 Makes Sense on a P38

The target tyre size for this setup was 265/70 R16.

This size offers an excellent balance for a largely standard Range Rover P38:

• Increased ground clearance compared to the factory size

• No need for body trimming or suspension modifications

• Works well with the original drivetrain and gearing

• Maintains good road manners and reliability

In practical terms, moving from the original ~29-inch tyre to a ~31-inch tyre noticeably improves off-road capability without introducing the downsides that come with oversized tyres.

If you want to verify how different tyre sizes translate to real-world diameter, clearance and speedometer deviation, you can use my P38 Tyre Size Calculator here:

👉 P38 Range Rover Tire size calculator page

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Final Choice: Cooper Discoverer S/T Maxx

After searching for quite a while, I eventually found a tyre that ticked all the boxes:

Cooper Discoverer S/T Maxx – 265/70 R16 121/118Q, 10PR, M+S, POR

This tyre sits firmly in the aggressive all-terrain category and is clearly aimed at heavier vehicles like the P38. Key characteristics include:

• Strong and predictable off-road traction

• Reinforced carcass and sidewalls

• Excellent durability for mixed on- and off-road use

While it’s technically still an all-terrain tyre, it’s very much on the tougher end of the spectrum — which is exactly what I was looking for on a heavy 4x4 like the Range Rover P38.

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Fitment and Expected Results

The tyres will be mounted on the original 16-inch alloy wheels, which will first be painted black to complete the overall look.

This setup should provide:

• A clear improvement in off-road capability

• No negative impact on drivability or comfort

• A clean, factory-plus appearance

Overall, it’s a well-balanced upgrade that suits how the P38 is actually used, rather than chasing tyre sizes or specifications for the sake of it.

Range Rover P38 Transfer Case Failure – Diagnosis and Replacement Plan

After only 1,000 km, the transfer case on the Range Rover P38 started making a significant amount of noise.

Initially, I suspected an engine-related issue, as the noise appeared to come from the front of the vehicle. After further investigation, however, it became clear that the transfer case (TC) was the real culprit.

Before reaching that conclusion, I even considered the gearbox as a possible cause. To rule that out, I replaced the gearbox oil and filter twice — without any improvement.

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Confirming the Transfer Case Failure

The real confirmation came when I drained the oil from the transfer case.

The condition of the oil immediately raised red flags:

• The oil looked heavily contaminated

• Metal particles were present

• The small internal mesh filter was completely clogged

At that point, it was obvious that the transfer case was the source of the problem.

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Finding a Replacement Transfer Case

Fortunately, I managed to find a second-hand transfer case. That did require a four-hour drive to pick it up and bring it home — but sometimes that’s the price you pay for the right part.

Of course, there was still some doubt in the back of my mind:
What if I install this unit and it turns out to be just as bad?

To avoid that risk, I sent the replacement transfer case to a specialist company capable of inspecting its internal condition.

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Good News at Last

Yesterday, I received the verdict — and it couldn’t have been better.

The transfer case was described as “brand new on the inside”, showing no signs of wear and requiring no rebuild or additional work.

That was a huge relief.

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What’s Next

With a confirmed good replacement unit ready to go, the next step is straightforward:

• Remove the old, failed transfer case

• Install the replacement unit

• Finally get the P38 back on the road

After a string of setbacks, it’s great to have something go smoothly for once.

More updates soon 👊

P38 Borg Wagner
transfer case

Rear bumper and spare wheel carrier

Finally finished the installation of the rear bumper and carrier. 💪

We’re back on the road with the p38!

Finally the p38 is back on the road since it passed technical inspection last week!

I’m so happy after all this time to finally be able to drive it. 

Past weekend I installed on off the many upgrades still to come on this vehicle, the roofrack by mp4x4.

P38 head unit replacement update!

Since I own the car I didn't look at the radio because it didn't work anymore. I did not have the code for the old radio and the display wasn't working anymore either.

So I decided to install a new more modern unit instead. However it is not plug and play. The car is equipped with 10 loudspeakers and each door has its own amplifier.

In order to make it work you either buy a loom to go from the stock iso connectors to an interface and then connect to the newly provided loom from the radio brand manufacturer. Or alternatively you rewire the speakers to allow you to use the radio's amplifier and 2 or 3 way speakers.

I managed to source a loom with an interface on ebay from the company Icarsoft. This makes it plug and play.

I choose a 1 din unit with bluetooth and dab, digital radio from kenwood.

I still need to finish the installation but I wanted to go ahead and try it at least. I also have speakers on the way to replace the old door units.
More to come soon.

In the meanwhile the speakers have arrived and are installed! Very happy how they sound on the original amps.

P38 new tyres

Et voila a new set of tyres are mounted on the 20” wheels. They will primarily be used for daily driving.

I will have another set coming soon with more off-road focused tires on 16” wheels.

That is if the car passes MOT.

These are Continental crosscontact Atr 265 45 R20

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P38 suspension upgrade

The Range Rover p38 is quitte a heavy car and it suffers from body roll, at least mine does. 

Because the goal is to travel with the car, weight will be added in the back under the guise of a small kitchen and dual battery system.

After some reading online I found that many people appreciate the better Bilstein gas struts for their p38. So I went ahead and bought a complete kit front and back.

Installation is fairly easy, I took of the wheels for better access.

You immediately notice that they are firmer because there is less body movement.

I took it for a short spin and let me tell you it’s a night and day difference already. Maybe the smaller wheels make a difference as well but that remains to be seen.

Anyway it’s well worth the price and surely one of the best upgrades I did.

The wheels had to come off anyways because I also bought new tires. Nothing aggressive they are 20” after all. But they'll serve as a my summer set.

P38 head lining installed

 Finally I came around to install the head lining on the p38. Getting it back in was no joke. Extra hands are needed if you want to successfully install it. 

It looks a lot nicer and cleaner. Another small project of the to do list.