3.0 runs significantly COOLER on full SYNTHETIC oil!

[fixizin]

Back in early February I gave my low-mileage (52k) Vulcan a "transfusion"... got a sweet deal on a K&R filter and... Pennzoil Platinum 5W-30, and immediately noticed the (factory) temp gauge was down at the 20-25% point, rather than the usual 45-50% range.

At first I thought well, it's "winter" (So-FLA style, lol), and maybe I just haven't been paying attention, but... now it's roasting season and that needle hasn't budged!

Now I've never had an overheating problem with this truck, even off-roading in the deserts of NV and AZ in July w/ the A/C cranked, but this has been kind of eye opening, i.e. as to how much of the heat generated by such gasoline engines is FRICTION--I would've "guessed" it was minimal compared to COMPRESSION and COMBUSTION, eh?

Also, would using synthetic oil early in an engine's life prevent "proper break-in"??

 

[RonD]

Your thermostat is stuck open, just below 1/2 on the temp gauge is 190-200degF, that temp is controlled by the thermostat(192degF t-stat), it isn't, and can't be related, to the oil you use.

Start engine cold feel upper rad hose, let engine idle foe a minute or so feel upper rad hose again, it should still be cold, wait another minute or so, feel it again.
If upper hose seems to be heating up with the engine then t-stat is stuck open.
Upper hose should not be warm for at least 5 minutes, 8 minutes on cold day

Synthetic oils can run a few degrees cooler than "regular oil", that is usually because it does reduce friction better and has a constant viscosity.
Most of the oil heat comes from cooling the pistons and cylinder walls, and the temperature of the oil passages in the block, so temp difference would not be alot, 5-15degF maybe.
Seen some claims of 50degF lower, that is great, hard to believe but still great, but it wouldn't effect coolant temp gauge in the least, minimum operating temp is set by thermostat not oil temp.


You would want to use "regular oil" for break in, unless you are RICH, lol, because you need to change the oil a few times during break in.
You could use synthetic, it would just be very expensive to do

 

[gw33gp]

I agree with RonD's statement about the thermostat. The only time I have seen a significant change in engine temperature by using synthetic vs. conventional oil is in racing. Cooling capacity is in more control of the engine temperature of a full on race engine and you can see the effects of the lower friction oil more readily. Some racers replace the thermostat with a blanking sleeve. I like a drilled thermostat to get the engine up to operating temperature quicker.

The statement about break-in is true of older engines but is not needed in modern engines. You can read the owner's manual and the only thing noted about break-in is to not hold at a constant rpm for expended periods for the first 1000 miles or so. They like to see a variation in speed. I just use the oil that came in the engine from the factory for the first 2,500 to 3,000 miles, then do an oil change with synthetic oil and start the recommended oil change interval. With my Ranger I use an extended oil change interval with an additional bypass micron oil filter. The standard filter still gets changed at 5,000 miles but the synthetic oil goes 20,000 miles. At 185K miles the engine still runs great and so does my old 89 STX (at 250K miles) which also had the extended oil change interval. Neither truck use any more oil at the high mileage than they ever did (about 1 qt. in 5,000 miles) which included a lot of towing all over the country.

 

[fixizin]

That DANG thermostat! (*shouted to the tune of "those dang kids!" *)

So mah Vulcan is running too cold, even in summer? Less than optimal cylinder head temps?...

WAIT... are you telling me that t-stat has been significantly throttled-down forever, even stop-n-go in summer heat, but it is now somehow stuck wide-open???

I'm tellin' ya, now a days it NEVER gets up to the old halfway mark, even after 60 minutes o' town driving, tropical sun beating down on BLACK Ranger...