Bruce In Philly

I've felt the same way... but.... what if the temp is being pulled after the radiator and after the thermostat before entering the engine? It is possible that the engineer's intent is to always shoot in stable 175F water into the engine... there is an assumption, maybe a false assumption, that when the engine is at operating temperature, the thermostat is wide open? Maybe it is not. If you think this through, letting the driver know the water supply is above what the engineer's want, is a sign the cooling system can't shed heat fast enough. It makes sense.

If the water temp is taken as it leaves the block, it would be up and down and not tell you anything... you would have no idea if the cooling system is keeping up and the system is in runaway. I am still thinking the dash needle is correct.

BTW, my 2000 Boxster's needle was always solid at 180F.... but then I sprung a leak on a hot day and that damn thing sure shot up........ it was working and the only time I saw it move up.

Peace
Bruce in Philly

Petza914

I think you guys may be confusing each other. Looks like on the 996 there is an actual water temp gauge, but not an oil temp gauge. On the 997s, there's an actual oil temp gauge that might have some light smoothing but is mostly accurate, whereas the 997 water temp gauge is really useless and like an idiot light. Mine never moves off 175 once warmed up even though oil temps can vary from 180-250 F.

Wayne Smith

Bruce, you make an interesting point, but if you were accurate, can you explain the 175F reading for those who have put in the low temp thermostat? Wouldn't those cars read 160F? Or are we balancing that accurately at 175F?

I'm more inclined to stick with the 175F being fake, but you've definitely provided food for thought. I appreciate alternative theories!!!

Petza914

Once a 160 degree and a 175 degree thermostat are both fully open there is no difference in the engine temperature. The advantage to the 160 degree low temp thermostat is that it starts opening sooner which means the engine is in a warming up state for a longer period of time. The theory is that it's this slower warm up that is thought to reduce bore scoring as it prevents cylinders 3 & 6 at the back of both banks from getting as hot before they start cooling since coolant is flowing to them sooner with the 160 thermostat than with the 175 thermostat.

docdrs

Very nice synopsis Pete. Makes you wonder why they even put a thermostat in these engines. Basically only needed to provide heater warmth on those cold mornings faster. The carbs needed them to help warm the intake manifold faster to help with fuel atomization for faster smoother and more efficient engine performance. The absence of the thermostat would also increase flow and cooling to the score prone areas. It would be interesting to see what the operating temperature would be without a tstat.

Wayne Smith

Pete, we're taking a left turn here, I think, but what are discussions like these for?

It is my understanding that bore scoring is more likely to occur in cold climates. That is, in places where the motor runs cold for a longer period of time. There are many who are smarter than I who tout the colder thermostat, but I continue to struggle to understand their arguments. It seems to me that getting the motor to operating temperature quickly would be a goal. It is argued that idling a cold motor is a bad idea. You should get driving as soon as the idle drops and get to full temperature ASAP. The 160F thermostat seems contrary to that goal.

My point to Bruce was that if the temperature is measured at the inlet to the motor just past the thermostat then, for his point to hold, the cooler thermostat should show a lower value on the water temperature gauge. Since it does not (I think that is a true statement) the conclusion would be that the gauge lies.

Wayne Smith

Odd as it seems from the standpoint of thermodynamics, free flow through the radiator can cause a problem wherein the coolant doesn't have time to cool. If you ever have a thermostat failure in the middle of nowhere running up and down desert streams in your 58 ******, don't remove the thermostat completely. Instead, cut out the center core only and put the body back into the housing. I speak from experience.

The thermostat is needed for regulation. Bad things can happen without it.

docdrs

On the 997.2 the sensor is before the thermostat at the top passenger side on a return from that side. All the tstat does on these engines is allow hot coolant flow out of the motor. The pump is what sucks and pushes the coolant thru the motor. On a winterday the motor would likely run too cold. But for the hot days it would definitely keep the motor a more uniform temperature with a less restricted flow. Cold day start up bore scoring is thought to be more of reduced lubrication from increased oil change intervals from what i understand. Yes I know that is just one of the multifactorial theories on the cause. Although a *****'s is not a flat 6 , your thermodynamic theory of reducing flow to increase cooling intrigues me. I could see how the overall pressure required to pump the coolant to the further reaches may be compromised but I would like proof as this is a closed system

Wayne Smith

Just a quick search came up with a lot of sites indicating the need for a thermostat. Here is one for instance ...

https://www.reddit.com/r/MechanicAdv...e_overheating/

I learned this from the best mechanic and driver I've ever known. Phoenix in the late 70s. Known as The Wizard at Beeline Raceway.

With the sensor where you describe it, I am more and more convinced that the temperature gauge lies!!!

Petza914

Wayne, it's a little counter-intuitive, but follow along and let me know what you think.

It is believed by some that the reason bore scoring is more prevalent in colder climates is because of the temperature extremes that exist in adjacent parts within the engine for a very short period of time. Let's look at an extreme case and say you park outside in MN or WI for 4-6 hours to tailgate and watch a Vikings or Packers game in the winter, at temperatures well below zero. When you go to start your car after the game, just about everything is pretty close to the outside temp - block, pistons, cylinders, coolant, etc. Now the car is running and you have hot explosions of fuel happening in the cylinders which start heating the pistons, causing them to expand. These explosions are also heating the engine block, but the block is a much larger mass of metal than each piston, so a larger heat sink, and if the pistons expand faster than the block (cylinders), tolerances become too tight and you score the cylinder walls, especially if oil isn't flowing well, because it's still cold and thicker. Add to this that during the initial warm up cycle, due to emissions regulations, the car has enriched the fuel trim mixture beyond the ideal stoichiometric combusion ratio of 14.7:1 (lower air/fuel ratio #) in order to warm the cats faster and start eliminating combustion pollutants sooner. This is why when it's colder out, the initial idle is elevated and the car exhaust sounds meaner - it's because there is extra fuel making it's way into the exhaust, combusting there and heating the cats up to get them working more efficiently sooner. So now, we have extra fuel in the combustion chambers which can also wash some of the oil off of the cylinder walls, lessening it's ability to lubricate the cylinders. As an aside, this effect may actually be worse in the DFI motors where fuel is being directly injected into the combustion chamber and also why all DFI motors tend to build up more carbon than non DFI motors, but back on topic... Also, it looks like in many cases that bore scoring is down low in the cylinder and caused by contact between the piston skirt and the cylinder wall, not from the piston rings that are designed to seal with the wall as the piston moves in the cylinder. This is why when checking for bore scoring, boroscoping the cylinders through the spark plug holes sometimes doesn't reveal scored walls as well as moving the cylinder to the top of the combustion stroke and scoping up from the bottom after removing the oil pan.

So in a really cold climate, you've created kind of a perfect storm inside the motor - thicker oil that's not flowing all that well, extra fuel washing the oil lubrication from the cylinder walls, and really hot expanding metal next to cold metal that's not expanding as fast with very tight tolerances between the two due to the high-compression of these normally aspirated engines.

What the lower temperature thermostat does is open sooner and with coolant starting to flow through the engine block passages earlier than with the higher temp thermostat, it's actually doing 2 things - 1) helping to warm the engine block sooner, which causes the cylinders to start expanding, and 2) the flowing coolant helps to more gradually even out the heat throughout the block - the heat that's being generated by the combustion process inside the cylinders themselves. If the thermostat remains closed because it doesn't start opening until a higher temperature, these benefits don't start until later in the warm-up cycle.

So now instead of having really cold engine block metal right next to really hot piston metal, you have warmer engine block metal next to really hot piston metal and as the engine block warms it expands, potentially enough to not constrict the hot piston and eliminate the contact with the cylinder wall, thus preventing scoring of the cylinder wall.

Now that being said, not having a thermostat at all would probably not be a good situation either, as it would take far too long for the motor to reach an efficient operating temperature, which means condensation from the warm-up cycle would remain in the oil longer, and people who use their cars for mostly short trips around town would run into milky oil issues, what looked like overfull crankcase problems, which can then result in frothing of the oil as the crank contacts it (this is what a windage tray that's in some of the deep sump kits prevents), no heat in the cabin until they arrived at their destination, etc so it's a matter of finding the right balance to make all the subsystems get along.

It would be interesting to find out if anyone who had a bore scoring issue had been running one of the low-temp thermostats for most of their engine's life and for a lot of miles prior to the scoring making itself evident, but there are also too many other factors that could contribute as well, so unless a scientific study is done by someone with all other factors being the same, except the thermostat, it's impossible to draw a conclusive cause/effect relationship. These other factors are things like the type and weight of oil used (and for used cars, that info from the POs may not be available), oil change service interval, following a proper warm-up protocol before driving aggressively, etc.

To your point about idling the cold motor being bad, yes, I agree, but it's my understanding that there are at least 2 reasons.

1. On a 997.1 car with the IMS Bearing (which I know you don't have and is completely unrelated to the temperature and thermostat discussions), the load on the bearing is the highest when the motor is at idle. As the shaft spins faster, the bearing self-centers and essentially spins with very little load on the races or individual *****.
2. As I mentioned earlier, there is an enrichment protocol that happens during initial startup to heat the cats quickly. Sitting there at idle during this process is not as good as being underway, as the extra load on the motor from driving actually helps to utilize this extra fuel in a more positive way, preventing the oil dilution and also warming the engine and cats more quickly.

Anyway, your filter media looked great

Wayne Smith

The way I see it, heat flows to cold, not the other way around. Science supports this premise. Also, objects with more thermal mass heat up more slowly when supplied equivalent energy.

What this means to me is that the pistons warm up faster than the block (which has much more thermal mass).

I figure the goal should be to heat everything up equally.

Any coolant running through the block (not supplying heat, since it is not a source of energy ... no burning) impedes the block's heating up making this worse.

More coolant through the block means a longer time while the overheated (relative) pistons are damaging the cylinders.

So during warm up, my goal would be to keep the thermostat closed.

I used the term thermal equilibrium some months ago and upset a fellow Forum member. So I make this next statement with prior apologies ... engine wear occurs most while the entire motor is reaching thermal equilibrium. This is not thermal equality. That is something different that is not a reality. Ideally all parts would heat up proportionally to each component's operating temperature, allowing thermal expansion to keep tolerances at their best. But I realize this is an over simplification.

You make very good points about fuel mixture. This is one of the reasons we want to get our motors to operating temperature ASAP. Again, an argument in my mind for the higher thermostat.

As for DFI, Porsche seems to have done a much better job of keeping things clean than, say, BMW. The early press releases indicated a spray overlap onto the intake valves. I've read this isn't what really happens, but how many of us have had to toss nut shells into our intakes?

I might argue the opposite ... that without DFI, in a cold motor the chill of the intake manifold creates fuel condensation with a poorer mixture reaching the chamber ... a mixture more prone to large droplets that might be more inclined to not fully vaporize, more likely to not burn, and more likely to wash the cylinder. At least, that could explain why the 997.1 cars suffer more than 997.2 cars.

Yeah, I was very happy with the filter. This speaks volumes in my mind to the quality of the cars we have the privilege of caring for.

caslca

WTF, I came here to read what is the best oil this month.

Wayne Smith

Mobil 0-40, but Pete is going to deny this 8)

Mike Murphy

The thermostat won't affect bore scoring. The thermostat actually helps get the engine up to temps (from 0-160) faster, sooner, and then it helps keep the engine at operating temp better than no thermostat. The difference between 160 or 180 t-stats also won't make difference for bore scoring either.

Bore scoring happens at low temps with oil that doesn't flow well at low temps. And even worse when some folks put the hammer down before the engine and oil are warm enough to lubricate. And happens at very high temps as well if cooling is off the charts.

You can actually hear hear many of these flat 6 engines at cold start. They sound "loose." You can hear all sorts of noises. It's important to get good oil that flows and get the engine up to temps before using a lot of throttle or revs.

Petza914

Wayne is right, I am - don't want to disappoint

IMO, best is Joe Gibbs Driven DT40 which is a 5W/40 unless you're under a Warranty where it has to be a Porsche A40 approved oil, in which case, the best is Motul xcess 8100, also a 5W/40.

Attached are my 2 most recent UOA reports from Blackstone on DT40 - one from my wife's NA 3.8L 997.1 and the one from my supercharged 3.8L 997.1. In the charts, her last 2 changes are DT40 with the 4 prior being the Motul. In the charts on my RUF car, the last one is DT40 with the one prior being the Motul. Note in all cases how the levels of Zinc & Phosphorous (two of the main components critical to preventing valve guide and head wear in our engines) are significantly higher with the DT40 than with the Motul. Based on the results from a 5,000 mile change interval when I was running the Motul, I was gradually reducing the mileage interval to try and achieve higher Zinc & Phosphorous levels, and also looking at the TAN & TBN numbers, along with the viscocity #s until I achieved results I was happy with. With the DT40, the numbers are so positive that I'm going to start working my way back up to a slightly longer mileage interval, so the next change on my wife's car will be done at 4,500 miles and if that looks as good, back to the 5,000 miles which makes it really easy to keep up with when a change is due. The RUF will likely stay at the 4,000 mile change interval because of the additional stresses on the motor from the supercharger, the way that one is driven compared to my wife's, and that I can't afford to have anything happen to that motor or car.

Hope some of that is helpful since quantitative #s are always better than just spouting off about what makes this better than that.

...and now it has become another oil thread