What i put in bold is where you and i are having a problem. I was responding to the question of High HP or modified engines. Let me give you an example. GM3800 GENII stock, manufacturer publish a spec and with an oil pressure and temp gauge i agree you can use that as a starting point, no problem. I am in full agreement with you so far. But now add a forged crank, high volume pump, bigger cam with modified heads and a 16 psi turbo. now what? The manufacturers spec just went out the window for the most part. So lets say i have both gauges and everything looks good on 5w30 then coming of an highway on ramp i hammer it. There is no way from the guages for me to know if the crank hit the bearings or not. IMHO this is the correct way to get around this issue. By all means keep the gauges but go up a weight from OEM spec like Mobil 1 0w40 or 5w40 make sure the op and temp are good, then do a UOA and another to see which way the wear metals are going. Do quite a few UOA's so you can see a real trend not just a one off from break in. That's the only i know f to find out if lead or aluminum is being shed from the bearings. If the UOA's are good then i see no point in going thinner, why mess with a good thing but if they show wear is excessive then decide which way to go or what to do to fix the issue. I see no way the gauges could provide me all the info i need to base my oil decision on without multiple UOA's in this engine. High spring weights, double roller chain and huge crank shock loads are sure to play havoc with the oil.
Originally Posted By: CATERHAM
There are many reasons why heavier oil grades are specified by some manufacturers but that is a separate question to your original point that, "Adding an oil pressure gauge is not a bad thing it is just not going to give you enough information under all conditions." What I've tried to explain is that statement is simply not true. An OP gauge (in conjunction with an oil temp' gauge for very high temp's) will tell you what you're operational viscosity is in a running engine; nothing else will. What an OP gauge will not do is tell what OP level is too low if that info hasn't already been determined. Your original comment about an OP gauge not being able to pick up crank flex is immaterial since that is not the purpose of an OP gauge. But if you knew that the operational viscosity level associated an OP level of say 45 psi did allow metal to metal contact under maximum load when crank flex occurred and that 50 psi didn't, then an OP gauge would be a very useful tool indeed to establish and maintain the minimum operational viscosity requirements to deal with that particular issue. Every engine has a safe minimum operational viscosity that can be readily established; the manufacturers OP test spec's are a good place to start.If one is going to experiment with different oil viscosities I know of no other way to keep track of where you're at than with the use of OP and OT gauges. You could drop down an oil grade to a 20wt from a 30 wt, run a UOA and get a good result but it still wouldn't tell you what you're really doing in terms of actual operational viscosity; you're still experimenting blind. Did you test the OEM OP test spec's and if you did how often and under what conditions? When you thought the engine oil must have been really hot on that 100F up hill climb, was it really? It's OP and OT gauges that tells you what really going on.
Originally Posted By: Trav
That makes the assumption that a 2.6 cP oil is enough to protect a high HP/output engine under all conditions it might encounter. The Europeans don't seem to have much faith in this theory, most of their oil for these engines are HTHS 3.5+. You can say i am over thinking this but i would say you are under estimating the importance of HTHS and block/crank rigidity and the boundary film offered by higher HTHS oils in engines that by design require it. Marine engines are a perfect example of the necessity of stiff blocks and bottom end. GM in this case has gone to great lengths to stiffen the bottom end. http://gmpowertrain.com/2013_pdf/FHR_REV_6.0_Marine_010713.pdf My question to you is why do they bother going to 6 bolt mains and super stiff block if the most relevent criteria is maintaining oil pressure with an oil of 2.6 cP? Like i said i have no problems whatsoever using xw20 or xw16w oils in engines designed for them but they are putting warnings out for the xw16 oils about backwards compatibility. Why is that if the xw16 with less than 2.4 cP couldn't be used in any engine as long as they can maintain oil pressure? Could it be that unless the engine was specifically designed for this oil a less than 2.4 cP isn't enough to protect the engine? Couldn't the same be said for a 2.6 cP oil in an old school engine? I believe it could. I guess you and i will have to agree to disagree on this magical 2.6 CP number is able to provide optimal engine protection in any engine under any conditions.
Saying that you can't run a 2.6cP 20wt oil (or even something lighter) in an engine implies that you can't maintain adequate OP. Because if you can maintain the previously established safe minimum OP then by definition you are maintaining an adequate operational oil viscosity