Get a cuppa. Lengthy story about modifications done while under warranty. And a good lesson on the importance of temperature and viscosity. ��
2005 I buy a new Harley TC88 dresser. These motors hold about 4 quarts of 20W50 and have a spin on filter. Gerotor oil pumps and the timing chains use a resin shoe to hold tension. Not equipped with a cooler or thermometer and they run HOT. These resin chain tension shoes are considered consumables and are routinely changed every 30-35K miles. No uncommon to replace the chain every or every other service.
On the first oil change and observing oil tank temperatures over 250F I swapped the Harley oil for Red Line HP 20W50 car oil. On the next change I bought a cooler system for a Sportster which, unlike the kit for the TC88, filters the oil before cooling it. It's a sandwich plate. I also bought a second TC cooler, just the radiator. As the sandwich plate extends the filter toward the frame to the point it cannot be removed, I also bought a new factory filter mount. Cut the filter portion off in the bandsaw and machined the block side to make parallel and groove for "O" rings making a 3/8" spacer. Replaced the mounting bolts with longer studs moving the filter forward enough to clear the frame then mounted both coolers in series. Searched the WIX catalogue for a cheaper, larger filter with the same relief pressure and crossed that to a Purolator. Added a pint or so and much cheaper filter. Took it for a ride and now I had oil temperatures on a 100F day of 190F at 70 mph dropping it 60F!
Third change I swapped the RLHP 20W50 for RLHP 10W40. Made blinds for the coolers and maintained an oil temperature of 185-200F for the next 45K miles. Yea, 10K past the service interval at which point the dealer is going nuts and telling me horror stories of guys have complete motors replaced due to the chains eating the shoe steel backing the sending that crap through the roller assemblies. He was sure the 10W40 non-motorcycle oil would be a killer. So, after a while I caved in and had them open the cam chest for service. As I did not want my pushrods cut and adjustable installed (Harley procedure) I had them remove the rocker boxes as well.
My instructions were to measure EVERYTHING and replace ANYTHING not inside NEW spec plus install the new HD high volume pump and new hydraulic tensioner system that came out a few years later. My Shovelheads would be due for overhaul by this mark.
Next day I get a frantic call from the service manager. "You need to come see this or you won't believe me." Cold sweat I hurry down to the shop. The entire shop is gathered around my bike. I squeeze through the human barrier to find my mechanic sitting on his stool having a cuppa with a big grin on his face.
Not a single part of that motor was out of spec. Not even a track in the cam lobes from the lifter. Not a hint of deposits. The shoes? About 10% used up! They would go 100K miles twice over. I had the new system installed anyway and buttoned up. The increased oil flow volume now has me running one cooler blind on everything but the hottest days in the desert. She runs ambient plus 90 degrees and whisper quiet.
Known problem. I fixed the problem. Ignored the warranty implications. I got rewarded for fixing the problem. Not with just havening no warranty issues but by adding multiples to the engine's life. Still own that bike.
AW and EP additives do NOT work on polymers and resins. Straight up viscosity result.
10W40 at 190F is many times more vicious than 20W50 at 250F plus.
Viscosity is a function of the oil's environment, not it's specification.