Havoline Energy is very good, I used it for more than a year, at may improvement sa responsiveness at translated yan eventually to fuel mileage. Its because its a thin oil, so less resistance on the moving engine parts, putting more power on the wheels, so in effect, better response, less use the gas. I'm just a city driver, and though conscious of performance, I don't stress my car ;)
Its downside I noticed is, medyo mabilis siyang umitim (but this also means that its cleaning the engine well), at 30 lang ang rating niya (5W-30) so less protection sa engine on very high temperatures.
In my opinion, ang paggamit ng thicker oil viscosities so that hindi magleleak ang thin oils mga old engines is just a "workaround". Solve the leaks on your engine, replace what needs to be replaced, seal whatever is leaking. Then use the oil that would be the best for the engine.
When I bought a surplus engine, my friend had it change oiled to Catsrol GTX (20W-50). Wala pa akong alam at pakialam sa mga engine oils nun, though alam kong may maliit na leak doon sa valve cover nung engine, hinayaan ko lang, parang hindi lang nakaayus mabuti yung rubber gasket sa palagay ko. Then nung malapit na akong mag due ng change oil, I began to study engine oils and the advantages thin oils can do. We had the valve cover opened, cleaned, gasket realigned, then put it back again w/ high quality sealant. So ayun, no more leak whatsoever.
I risked putting Havoline Energy in the next change oil, hoping na hindi iyon magle-leak sa ibang engine parts na hindi ko nakikita. It did its job well, at hindi nag leak. Maganda car response, mararamdaman mo ang ka-labnawan ng circulation niya doon sa engine. To an extent, yes, it will save you gas. Used that oil for more than a year (kahit na tumagal, pinaabot ko talaga ng 5000kms ang oil na yun)... ayus padin ang performance kahit medyo nangingitim na.
Recently, nag change oil na ulit ako kasi due na eh, this time a more thinner oil, Mobil 0W-40 SuperSyn. Thinner than Havoline Energy at siyempre bagong oil, ramdam ko agad ang difference sa response, idling humming sound, at revving. No leaks whatsoever, for the past more than 150kms ko na ginamit walang bawas sa oil dipstick. I think I'll be sticking to this oil already, better protection pa on high temperatures compared to Havoline Energy. Still, my next best choice would be Havoline Energy.
In summary, Havoline Energy is a very good oil based on my experience as long as your engine has no leaks, highly recommended. For its cost, its one of the best priced quality thin engine oil. Again, if your old engine has leaks, paayos yun permanent solution, using thicker oil grade is just a temporary solution
