I claim no expertise whatsoever, and the interweb is full of misleading information to prove right is wrong or wrong is right and that I have spent quite a lot of time on Morgan forums since the mid 90`s reading of the possibility of issues arising resulting in the inability to build oil pressure immediately following an oil change on a +8 and do much else, I thought to ramble on through some of it .. though perhaps best not to depend upon my failing memory...(-:
As best I can remember the general +8 advice was not to drain the oil and change the filter together but to drain and refill the sump, run the engine to ensure oil pressure built up by monitoring the gauge, shut the engine off then change the filter, and as Richard suggests, as much as might be possible put as much fresh oil in the new filter as might be reasonable and re fit it, which on the +8 is a messy business but better that than ending up with risking the inability to build oil pressure following an oil and filter change.
Sure you are mixing old and new oil in the above process, but in reality there will ever be old oil left in places in the engine to cause a degree of mixing old and new... ?
I suspect the more worn the engine might be if you warm the engine up, to thin the oil with the aim of draining as much out of the engine as possible, changing the oil filter dry, then leaving the engine sitting to allow the oil pump to fully drain down over time.... Might be the worst case scenario in terms of risking failure to build oil pressure....?
I have also read of a failure to build oil pressure after a +8 oil change where the pump gears were packed with grease in a bid to increase it`s ability to initially build pressure, which seems a tad extreme but if the pump gears are worn then I guess that could be a work around...?
It seems so much has changed in engineering tolerances and materials used and that lubricants seem to have gone through a similar process of evolution to the extent that it seems very specific lubricants may be specified for equally specific engines, and that modern synthetic oils seem to be so very different from the old mineral oils that were around when the likes of Triumph TR`s or Rovers used the engines that found their way into Morgan engine bays...?
Thin synthetic oils in a worn engine with wider clearances in it`s moving parts would seem likely to create possible pressure building issues. I think around the time that synthetic oils arrived on the scene that Castrol created their MAGANETEC which seemed to suggest that this oil would adhere to bearing surfaces and be less likely, or take longer, to drain back down to the sump as the result of a mix of time and gravity, thus risking the horrible rattle that old engines that have been laid up for months on end can develop when they fire up initially, until oil can fill all the gaps in the bearing surfaces to begin building up oil pressure...?
It seems there are some oil producers who claim to specialise in providing oils which may be more suitable for old style engines... Millers oil..? There will be others, but just how much of that might be smoke and mirrors or just business being business... I have no idea.
Much has changes since the days of removing cylinder heads to de-coke them was a semi regular task, On the few engines I rebuilt I used to spin them over on the starter motor with the coil disconnected to prevent them firing up, till the oil pressure light went out before allowing them to fire up..
It seems the mix of engineering involved betwixt metallurgy and the technological advance in oils seems to have greatly decreased the requirements for oil changes in some machinery, thinking sealed for life gearboxes on some vehicles..?
Porsche suggest bi-annual engine oil changes for the engines on their high performance machines, and are quite specific about the oils used. Just how much of that might be down to business arrangements as opposed to finding the best possible lubricant to suit their high performance engines serviceability...Matters not a jot to me, but I would not care to use any alternative.
Just to use Porsche as an example, since they went to water cooling with 911 derivative engines there seem to have been dogged by a measure of engine issues which at least one UK company have specialised in resolving, and this same company also suggest that a different oil is used in older Porsche engines which may be more suited than the oil Porsche specified when the engines were new.....?
I have run my mid 80`s +8 irregularly, only covering circa 30k miles during the 23 years I have been it`s custodian, thus it has spent rather a lot of time dormant between runs, but fortunately the old thing seems not to have suffered greatly as the result of my less than fastidious maintenance schedules relative to TIME, and fortunately for me still matches normal oil pressure expectations with the engine both hot and cold and the engine runs at a pretty standard temperature when hot, never having boiled over in my custodianship, though the driver and passenger have somewhat overheated when touring in much hotter climate zones, than here at home...(-:
As ever.... more than happy to be proven mistaken on any of the above, this is after all a discussion forum...? (-:
