Do you have a choice when your this far into the engine? Probably not and if you did have the choice you might as well go ahead and do the head gaskets if you have tore this deep into the engine. But I don't see how you could do anything with the sleeves without doing a head gasket job.

 

Lyroc & 99Discovery, Sorry I didn't make myself clear enough. let me see if I can help to shed more light on issues you have been discussing: Regarding thermostats and radiators, any change to a 180 deg. thermostat is a really good thing---=aluminum engines, with any excess heat, expand and contract considerably more than more traditional cast iron blocks (cast iron absorbs the heat much better, with no ill effects, than does aluminum), easily leading to failures from warped aluminum heads (a common occurrence with aluminum heads on ALL engines). Rover installed the hotter thermostats, so engines would run hotter, and heat up quicker, for more driver comfort, but more to enable engines to produce less pollutants, helping with pollution standards over time too. Heat, especially excess heat, combined with excessively thin aluminum coolant passage walls (created when Rover increased bore sizes to 94mm dia.), further combined with stretch head bolts exerting excess stress in critical areas, located very close to the thin aluminum coolant passage walls, all contribute to what we Rover owners are now familiar with, cracked aluminum walls (cracks occurring usually directly behind, and a very short distance from the base of the head bolt threads) behind cylinder liners, which loosens the cylinder liners, which causes liners to slip sometimes. For engines that were made the way Rover intended, once they recognized the problem, with the cylinder liners butted up flush against a cast aluminum shoulder Rover had cast in at the base of each cylinder bore, the liners couldn't and didn't slip during operation, but for engines that had the liners slip up slightly, generally about 1/8", during the manufacturing process (when they installed the liners, they heated the aluminum blocks considerably, and pressed in the ambient temperature liners, but during cool down, the liners sometimes slipped upward slightly, setting up potential for possible future problems with liners slipping during engine operation, which is what we have seen so much of). Now, let me try to answer your questions directly: "The 4.6 is the better engine, less chance of cracks in block and liner slipping," YES plus only "15% of all the 4.6 engines had these issues." YES "The 4.6 was made with a thicker walls which helped prevent cracks from happening." NO, not made thicker, it was just that Rover had been doing ultrasonic testing of all blocks, to determine, for sure, the thickness of the aluminum walls behind cylinder liners and coolant passages, and color code grading them according to the thickness of those walls. They used only the ones that turned out to have the thickest walls, color coded red, for 4.6 L. blocks, and used all other ones, mostly color coded blue, for the 4.0 L. blocks. " And the liners were fully butted up against the aluminum shoulders at base of each bore and flush against shoulders at their base, which keeps slipping from happening." Yes, for liners that were truly butted up flush against the cast in shoulders at base of each bore, BUT some were NOT fully butted up, as they intended, due to manufacturing glitch (see my detailed explanation above regarding this issue).
"Now the 4.0 is the engine to avoid of the two because it was more prone to cracked walls because the walls are thinner and the liners were not fully butted up against the aluminum shoulders at base of each bore and flush against shoulders at their base." See my more detailed explanation for this, above. " This occurred in 80% of all 4.0 engines." Yes, it did; no surprise, if you pay attention to the numerous discussions of cracked blocks and slipped liners on these websites. Following as many as 3 or 4 massive overheating events, the 4.6 L. engines often needed only head gaskets changed, with no issues involving cracked walls behind liners, no slipped liners, etc., while the 4.0 L engines often needed repair of cracked walls behind liners, slipped liner repairs, along with head gasket repairs, following only 1 or 2 massive overheating events. That isn't to say that a 4.6 is bulletproof; will not experience these problems as often; it is just to say that the odds are more in your favor with the 4.6, because of facts stated above. By the way, original Rover head gaskets are far from the best too; it is much better to use considerably more reliable, much better made high performance head gaskets, such as from Cometic, using their MLS or MLY multi-layer stainless gaskets, or simila--they make them to fit Rover. You can probably get them from Summit Racing. Intermediate head gaskets, such as Reinz or Elrings brand, are reasonably good too, not the best, but better than original Rover. If you do much Rover work, you know how important good gaskets are, and you can't get ones that are too good, especially if you don't like changing them often!
Regarding thermostats, I highly recommend conversion to inline system; that is exactly what I did on my 2004 Discovery. Read and follow this: Inline Thermostat - LAND ROVER CLUB V.I. but, use one or two different hoses, as mentioned by poster on THIS site you are on now, as they fit better (if you can't find that post, send me a PM, and I will let you know what the hose numbers are. " Would this be the way to go? Seems very nice and satisfying for the engine." Yes, no doubt about it. That is what I did, and am highly satisfied with conversion. Original coolant stem is PRESSURE activated thermostat system, pressure from heated coolant, while conversion is more traditional HEAT activated thermostat system. In the modification, the Meziere WN0071 is a beautifully made heavy aluminum thermostat housing, enabling use of traditional Chevrolet V8 thermostat, less than $10.; simple to buy anywhere, 180 deg., or even 170 deg., or whatever you want. Works wonderfully, makes much more room on lower right side of radiator, not cluttered up with that Rover plastic thermostat housing and related junk. Most importantly, it allows Rover to run cooler, with far less worry about possibly overheating issues and related serious problems and expense. For modificatiokn, Don't butcher your radiator shroud, for conversion, as some have done; it is not necessary. Keep that top radiator hose, from aluminum bleeding housing part of mod. to engine, as short as possible, just curling around the alternator pulley/belt, for great fit. When bleeding, be sure to remember to cover the alternator with heavy plastic bag, so as not to get coolant into alternator--(works for me). Radiator issues: When your original radiator gets clogged up, or breaks down and starts leaking, install only one of the good aftermarket ALL aluminum cross flow radiators, with size appropriate to fit into allowable room, no plastic, no junk, only good best quality all aluminum, same or preferably of more capacity for better cooling. Others have done this conversion, so do searches on this site to find details ."So earlyrover, engine-wise, is a 4.6 P38 a fairly safe bet, despite the 88C (190) T-stat?" Yes, but see my explanations above. Get rid of the 190 deg. stat, and install one of 180 deg. even if you have to do modification. The original Rover 96 deg. C. stat, its location within the coolant system; the original small radiator, all contribute to possibility of overheating issues. Beware, too, of course, to watch your coolant level, your water pump, your coolant hoses, etc. for any problems that may crop up over time, for problems with any of them can lead to serious overheating issues.

 

Supplement to my last post.
Found my notes on Radiator modifications as done by one poster, "EX Ternet" on this web site forum: Use GM Chevy universal all aluminum cross flow profile radiator, about $160. 16"x28'x2 1/8 core, 2.5" thick, or similar, preferably larger, as long as it fits in original radiator space, from KMJ performance, kmjent.com. All TIG welded; no epoxy/plastic/rubber to go bad.

For head bolts, do not use them; use only alloy head studs, such as from ARP.

 

Eldonkey: "Lets say a slipped sleeve does occur? What could be done to repair it? Cost? Would doing the head gaskets be advisable at that time as well?"

If you have an engine with one or more cracked areas behind cylinder liner, it can be repaired as follows: The liner(S), of course, must be removed, with liner(S) removed, the cracks are TIG (heliarc) aluminum welded up, a common practice, and machined down by good auto. machine shop, for fitting in new liners. Since you have done this much work, at this point you should have Top Hat sleeves (liners) installed, the ones with "o-rings" at their base. These Top hat liners, essentially, do three things, the "Top Hat" prevents them from moving up or down in bores, so they will never slip. The o-ring prevents coolant from moving down into the oil pan, should the aluminum behind a liner ever crack from serious overheating events, and the top hat seals way better than the original Rover liners (that have a sharp top edge that easily cuts into the head gasket, should the liner slip upward). If installing new top hat liners, of course, you have to put in new head gaskets, as you would have the engine out of vehicle, and in best auto machine shop for installation of the top hat liners (that sort of work is usually not done by most Rover owners, due to machinery needed for the work, and due to skill required to do the work). At same time, you would have same auto machine shop examine the heads for possible warping (all aluminum heads from all engines are very susceptible to warpage from overheating events), wear of valve guides, etc. Machine shop should rebuild heads to good condition; grind in valves.

 

earlyrover thank you for all this information. I will for sure be doing the thermostat and radiator swap/mods. I had messaged previously about swapping the radiator for a different radiator but no one seemed to know about another model of radiator that wasn't like the original. So thank you for providing me and everyone with a better radiator without all the plastic that's prone to cracking/breaking and a great alternative thermostat. These are two things I will for sure be doing as soon as I pick one up. Thanks