ahh good,, thank you for info will check the head number at first light Sunday,,I constantly watch the coolant temp and oil pressure ! and never drive her hard,, well perhaps I'll do one 0 - 60 to verify, stats,, thank you ps I'll keep an eye on the coolant level !!!! so far it's been good,,Cheers

You can drive it as hard as you want............you won't crack the head by doing so.

The problem comes when somebody loses a water pump, or develops a severe coolant leak. This engine will go from normal temperatures to well over 120C. in a matter of one minute under such conditions. Very few drivers will be on the gauges to detect this condition before damaging the engine.

Nothing much of a preventative measure can be done anyways. Adding a little water wetter to the coolant may or may not help. I have no opinion on that.

Another thing I have observed. The head casting hardness of the aluminium seems to vary. This has been reported by one member testing various heads at one time from these engines. I cannot comment otherwise either on that.

That said one thing that is never mentioned but should be thought about. A running engine has or develops local hot spots. Before turning the engine off it does not hurt in my opinion to let it idle for a few minutes to equilise the temperature and reduce it slower than otherwise in the hot spot areas. if present.

Also this allows the oil feed to remain on the turbo bearings until the turbo spools down. There will be less potential coking of the oil. Instead sucking heat away from the bearings and bearing seals. As the turbo winds down.

I think if I owned one of these engines I would make a small cool down period a general practice if the trip length was long enough that the engine had really gotten warmed up.

Another factor to consider is that the block being cast iron and the head aluminium may enable a more controlled even contraction of the overall head with a small idle run before shutting down the engine.

Where the cracks appear on these heads is not really random. The location of them might be consistant with too rapid expansion and contraction in relation to other metal in their proximity. Especially if they are a hot spot.

All that would result in my opinion by running these engines a little hotter than they should be is perhaps more stress in that area between the valves during the cool down period especially.

These ports are not far apart either. So a consideration has to be the influx of cool air into the intake and really hot air leaving through the exhaust port. But this is just an item that may add or subtract from things.

If a bubble in the coolant were to form or develop from that overheated area with fast shutdowns or hotter engines at shutdowns . That could do it easily in my opinion. The stresses then could go way beyond what they should or otherwise be.

How this engine has been used may contribute in some way as well. Theretically is a lot of short trips over the years versus a mix of short and long etc. The aluminium in that area just might eventually fatigue out.

Sorry for the long response. Especially since there is no way to really prove this easily. Yet it still will not do any harm, Even if what I think is totally wrong to let the engine idle for a minute or two before shutting it down in my opinion.

Good information I will address these items,, as for hot spots in head it is a valid point,, one the the big ones is trapped air pockets some heads will boil the coolant near the exhaust outlets . bleeding the head is something I do on the motorcycles,, difference in thermal expansion rates of block to head in my turbo Chrysler resulted in premature failure of head gaskets,,, in the 60's we used pure copper head gaskets on turbo bikes,, better heat transfer cooler heads,, and running 10.5 compressions copper gave use better sealing. I forgot about the cool down thing,, very good point,, will do !!!
one thing I ran into on moded bikes with turbos in the 70's,, after the oil leaves the turbo we had to use a large diameter oil return line in to sump,, the bearing and speed of the turbo would froth / whip up the oil and create bubbles.. we added stainless steel wool or wire mesh,,at the end of the return tube to break down the frothing,, net result was good constant oil at pump pick up point,,no cavitation due to bubbles in the oil ,,