Lots of opinions here and taking all the previous posts into account;
My feeling is max cruising speed 3500rpm on a light throttle. In my bus with standard transmission and almost stock diameter rear tyres, that equates to roughly 55mph (according to prat nav), so I sit with the big trucks most of the time. Very occasionally one will pass me (usually east european....) and several times I will pass them.
Theory is the engine is rated as max rpm 4500 so 3500 seems plenty for prolonged running and a light throttle means less stress on the engine. Also, seeing as that is close to peak torque, the engine is less stressed, fuel consumption will be at its best and you are at the prime spot if a bit more speed is needed to overtake due to being bored reading 'Eddie Stobbard' and 'long vehicle' for the last hour!
With standard running gear and the cooling system in full working order, driven sympathetically there probably is no need for extra guages. Whilst Jaguar, MG, and lord knows how many others fitted extra dials, VW didn't feel the need, even for extreme climates. Maybe drivers expectations were not so high and they were driven much more gently then....? That said, I would be happy to monitor oil temp/pressure. A mate of mine refers to them as 'worry meters', he may have a point?
Oil temp, if it were only 80 degrees, which is quite probable in recent wintery temperatures, I would be glad I had used a 15W/40 rather than a straight 30 grade but would still be wary of working the engine too hard. If the oil ain't overly warm then neither are the engine components, they probably are not at optimum temperature, treat it as a cold engine.
Lorry speeds, I am informed that the legal limit for over 7.5 tonnes are 40mph on A roads, 50mph on dual carriageways and 60 mph on motorways. That is the
UK limit on motorways, but this cowardly government kiss the arse of the EU and
recommend the 90kph EU maximum (56mph) which most HGVs are mechanically/electronically limited to.
In the 50s and 60s, 50mph was considered a more than respectable cruising speed, indeed many vehicles were almost flat out at that rate. Trying to make a standard (and probably worn/tired) engine from that era accelerate and travel at modern day speeds has to be a recipe for disaster.
All the above is 'just my opinion and heresay', please dont shoot!!!!!
