Here is a list of most of the common engine problems we've seen with the 4.0/4.6 Rover V8 found in the 1999-2004 Land Rover Discovery 2.
Head Gaskets
By far, probably one of the most common issues with the Rover V8 is its appetite for head gaskets. The 4.0/4.6 almost considers the head gasket required maintenance. Overheating is probably the most common cause of head gasket failures in the Rover V8. However, in some cases the gaskets do seem to just wear out on their own with mileage. The Discovery 2's unnecessarily complicated coolant system with the thermostat bypass loop did not help matters. To meet emissions standards, the thermostat ran the engine significantly hotter than before when it was used in the Discovery 1. Land Rover also specified the use of Dexcool coolant, which has known corrosion issues with aluminum parts (like the block and head of the Rover V8).
The coolant passage on a Rover V8 is ahead of the front cylinders and behind the rear cylinders. The head gasket usually fails between this coolant passage and the rear or front cylinders. Common symptoms include misfiring, coolant consumption, coolant system pressurization, and overheating. The only fix is to remove and replace the head gasket. The heads should be checked for warpage and machined flat. We have been hearing that at this point, many engines are on their second, third, or even fourth head gasket replacement, and the heads have been shaved down too many times to be reused – meaning that the only option is replacement heads, or our LS Swap Kit.
The other possible head gasket failures are between the cylinders (in our findings, typically burnt out between the middle two) or an external leak between the outside of the engine and a middle cylinder. The latter leak is commonly accompanied by a misfire and puffing sound. No apparent coolant loss is typical. Driving on these types of leaks can be damaging to the engine if the hot exhaust gas burns a channel through the block and head where the leak is, so they must be corrected quickly. Luckily LS engines don't frequently have head gasket issues!
Cracked Block
This is most commonly found on the 2003-2004 4.6 V8 Discovery models, but can be found on all Discovery models. These models got some of the worst Rover V8 blocks used (discussed more here). The tolerances in the casting were poor and in some blocks the coolant passages between the cylinders were closer to one cylinder than another. Because of this abnormal positioning, the closeness of the coolant passage to the cylinder creates a weak spot in the casting. These weak spots are susceptible to cracking. Typically this requires an overheating event for these weak spots to become known; however, there have been cases where cracks can form without an overheating event on very poor blocks.
Common symptoms with this include coolant consumption, pressurized coolant system, and misfires. This can also manifest by finding coolant mixing with the oil, although this seems to only happen with the worst cases. Since the symptoms are similar to a head gasket failure, many people unsuspectingly replace the head gaskets only to find that after replacement, they still have coolant consumption issue. The best way to tell the difference is to verify which cylinder coolant is leaking into. This can usually be help by checking the misfire diagnostics to see which cylinder is reporting a misfire. The front and rear cylinders (1, 2, 7, 8) are all near a coolant passage, so misfires in these cylinders frequently indicate a head gasket failure. If the misfire is in the middle four cylinders (3, 4, 5, 6), then you may have a cracked block because these cylinders are not near any coolant passages. The best way to verify this is a borescope. After removing the spark plugs, the borescope can be inserted into the spark plug holes to take an internal look at the cylinder. If you find that one of the internal cylinders is steam cleaned and has very little carbon build up compared to the other cylinders, you likely have a cracked block. This can also accompany the slipped sleeve problem detailed below.
The only remedy for a cracked block is a new engine. We, of course, would recommend that engine be a used or remanufactured LS V8 using one of our Discovery LS Swap Kits, so you don't have to deal with all the problems on this list all over again. O-ringed, top hat liners for the Rover V8 can fix this problem somewhat, but installation is quite expensive. Furthermore, we have heard lately of a number of failures of remanufactured Rover V8 engines, even from reputable sources. My guess is that the remanufacturers of these engines are running out of good rebuildable core engines. With engine supplies drying up, worse and worse Rover V8 engines are being rebuilt and sold to customers.
Slipped Cylinder Sleeves
This failure tends to accompany the cracked blocks and is especially common in the 2003-2004 Discovery 2 V8 models. The aluminum block engine has pressed-in steel cylinder sleeves. During assembly the sleeves are cooled and the block is heated while they are pressed in. There are lots of stories about this, but supposedly Land Rover changed the adhesive used between the block and sleeves at some point late in the production run to save money and the new adhesive was not as heat tolerant. Whatever the reason, in the later engines, the sleeves can actually slip up and down inside the cylinder bore. This usually manifests as an annoying low-end tap or light knock that will appear once the engine has warmed up and is at low RPM.
Slipping sleeves are usually tied to some overheating incident, but that is not always required. It can also be related to a cracked block – typically the crack occurs on a cylinder with a slipped sleeve. The sleeve itself bounding up and down in the cylinder can causes issues from constantly banging on the head gasket and head. This can make a circular-shaped indention in the head and can also increase the Rover V8's already large appetite for head gaskets. Once again, unfortunately, the only permanent cure for this problem is replacing the engine. We once again suggest that this would be a good time to consider one of our Discovery LS Engine Swap Kits.
Oil Pump Failure
While oil pumps can fail on any engine, they seem to fail on Rover V8s more often than others. Symptoms of this include the low oil pressure light coming on, particularly at idle (and then promptly going away when revved above idle). The oil pump gears can crack and, therefore, do not create the required oil pressure to lubricate the bearings, rods, pistons, etc. If replaced promptly, despite this job being a bit of a pain, damage to the engine can be adverted. However, if left, then the wear on the engine will probably mean a complete engine rebuild.
Some 2003 Discoveries also had an issue where there was a casting problem with front housings that resulted in low oil pressure. Most of the engines affected by this problem self-destructed long ago and it is not really something to worry about in Discoveries still running today. However, if you are looking at replacing the Rover V8 oil pump check to make sure that there is not wear on the front housing. If there is, you probably should replace the front housing, which is getting increasingly expensive and hard to find.
Walked Camshaft Bearings
This is becoming a more frequent issue with older Rover V8s. The camshaft bearings actually will walk forward partially out of their journals. These can then be worn by contact with the spinning camshaft. The only way to fix this is to break down the engine and replace the cam bearings – meaning, inevitably, another engine rebuild. Are you noticing a theme here?
Worn Camshafts
Another problem found in older Rover V8s – worn camshafts. If your Rover V8 seems down on power from its younger years it could be that the camshaft lobes are worn down. Replacement and higher-performance camshafts can be used, but replacement labor includes removing the front cover and everything above the valley pan. With the amount of labor this involves, I would recommend considering an LS engine swap, where you can get a significant bump over stock power.
Rod Bearings
We have pulled Discovery 2 engines apart at around 100,000 miles to find a bunch of less common, but still troubling issues. One example is rod bearings. After pulling all the rod bearings on one engine, we found that on nearly every bearing the internal copper was showing. The rod bearings really needed to be replaced. Good thing the vehicle was getting one of our LS swap kits!
Coolant leaks, Oil leaks, and more leaks
If you own a Discovery, or just about any car with a Rover V8 engine, you are no stranger to leaks of all shapes and sizes. The Discovery V8 has a few common oil leaks, notably the rear main seal (and other nearby seals), valve covers, valley pan gasket, oil pan gasket, and front cover. These leaks are typically expensive to fix because of the labor involved. Coolant leaks can come from the throttle body heater, the radiator, and the water pump. Coolant leaks can be particularly hazardous because of the other issues that they can cause through overheating like head gaskets, cracked blocks, etc.