Twinspool

Interesting topic. I must admit, I'm changing my mind as I'm learning more. I can see the reasons that the water cooling system is dumped on race prepped cars and I understand why Porsche put the little water pump on our cars since turbos had a bit of a bad reputation in the 80's. (Chrysler's fault)

I guess if I were running an oil cooled turbo on my car I would like to see a bit bigger oil cooler with temp. monitoring capability since the temps that the oil encounters in the turbo are going to be higher than anywhere else in the engine. This has to be a big contributing factor to oil breakdown. Synthetic oil is better, but the low viscosity is not what the 951 was designed to run on.

"Sure my oil cooled turbo is fine but the #2 bearing is shot and the lifters make noise!"


Bottom line is, I guess I was incorrect in assuming that water cooling was necessary on a street car but water cooling is definately "a good thing" as the Felonious knick-knack queen Martha Stewart would say. Just because the factory put it there and it was designed with that in mind. On another car that is designed to run oil cooling exclusively, like the 930, great! bring on the oil cooling!

MachSchnell

Well, if one were considering an oil cooled turbo, the simple solution, and the one favored in most turbo upgrades for factory built naturally aspirated cars is to simply place a larger oil cooler between the turbo oil outlet and the oil return...
As for the synthetic, why couldn't one just run 20W50 full synthetic? Being a FL fella, I've had nothing but great experiences with Valvoline 20W50 full synth, and it's less prone to the leaking associated with 0W or 5W, yet still retains the high heat capability of the synth...granted you would have to account for the veritable fountain of leaks that will inevitably develop from the higher detergent oil, but I'm a big fan...and will most likely be going with the synth for next oil change (mech stuck 20W50 mineral in after the head gasket change without a mobil 1 filter, much to my chagrin)

TurboTim

Jason,


I never said watercooling was the end all be all solution to turbo longetivity. I said it is not a great idea to rely on oil cooling alone and that we will not sell turbos which are cooled by oil alone. Sure a watercooled bearing section can coke if it is not "cooled down" properly. However, coking is caused by heat and a watercooled and oil-cooled bearing housing will produce less heat then just an oil-cooled bearing housing. Like I said before, water dissipates heat much better then oil.

Now here is a scenario for you to take into consideration. Take two pieces of cast iron and heat them up with a torch. Now dunk one of them into some water. Which peice of iron will be cooler to the touch? See my point.

I know you said that a turbo that was designed to be oil cooled alone should be as reliable as a watercooled turbo but......the oil-cooled turbos I have seen use the same watercooled bearing sections that come on our turbos, they just use plugs to cap off the water entry and exit. These bearing housings are not specially designed for oil cooling alone. They are just watercooled housings with plugs.

keith

KokelnRob said:
[quote] A turbo water pump, separate from the main pump, runs coolant through the turbo once it reaches a set temperature and turns off once it has cooled. Under normal driving conditions where the turbo does not go above this set temperature the turbo pump will not run once the motor is shut off. <hr></blockquote>

This is actually incorrect. The temps get high enough to cycle the pump after shutoff even with normal commuting.

As far as mechanics not drilling the waterpump blockoff, I would be one pissed mother if someone else serviced my car and "missed" that little detail...

It seems almost as if you are painting the water-cooling as a bad thing. That is ridiculous. It may not be necessary, from one's point of view, but you'll be hard pressed to prove it is a detriment to these cars.

IceShark

Keith, I don't think the point is that water cooling is bad just that is may not be necessary with a well designed oil system and this also has the side benefit of reducing complexity and failure points.

As far as this argument about water being a far superior heat transfer material in this application, I believe that is bogus unless someone can show me the significantly inferior thermal transfer rates of common oils. By using the example of heat transfer in un-pressurized quenching shows a lack of understanding of phase shift from liquid to gas. It takes 1 calorie per gram to raise water 1 degree C. The phase shift takes 540 calories per gram to shift water at 100 deg C to steam at 100 deg C. So take a look at the respective boiling points of water and oil at one ATM and you will understand why a water quench is a far quicker heat absorber. However, transfering that result to turbo cooling applications is meaningless unless you plan on flashing all your coolant to steam on a routine basis.

TurboTim

There is no lack of understanding on my part.I was trying to give an example in lame mens terms. My point was that having water running through the bearing housing along with oil will cool the bearing housing much more then having oil running through it alone.

StanUK951

Layman: Person not in holy orders or without professional or special knowledge.

Lame Men: Umm, a group of men with disabilities?

Sorry, couldnt resist that one! <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />

dand86951

Regarding water cooling the turbo for reliability, weren't the early 80 Audi 5000T turbo's oil cooled only? I had one and tried diligently to let the turbo spool down before turning the engine off and I still had turbo problems, all which related to the bearing section, either seals or freezing up. Fortunately for me these occurred during warranty but sure left a bad taste in my mouth.
My Audi was in Texas so it did operate under hot ambient, but after 16 years of owning a water cooled turbo, my 86 951, with no turbo failures, my vote goes for water cooling a street car even if it ran only synthetic oil.

For a race car without Air and without putting along in barely moving parking lots on 100 degree days and with very few actual running hours put on them I would agree that the simplicity of oil cooling would win out.

On another note lots of aircraft engines are oil cooled only. There are many accounts of aircraft turbos failing due to oil coking. Keep in mind these engines are usually on non boost, reduced power settings, for many minutes during descent and landing and taxi and it is still a known problem. By the way a lot of these are Garrett Turbos.

Just my two bits worth based on a lot of years around various turbo set ups.

<img src="graemlins/wave.gif" border="0" alt="[byebye]" />

SamGrant951

kokelns turbos also start around $1500, SFRs with water cooling start around 999...hmmmmmmm

MachSchnell

Now Sam's point is the best of all (and hearkens back to my original comment that I love the SFR offerings)...this is a case in point for mad props to Tim. My point was in no way to down Tim's comments per se, but more to assure those who were thinking of going oil cooled that it was not the horrid thing that an average joe might have implied from Tim's original post. Sorry Tim, I admit I took the 'end all be all' comment a bit too far, I was exaggerating a bit to make a point, but I was more looking to reassure those who might consider oil cooling that the troubles of the early 80s turbos (as referenced for the Audi above) are largely eliminated quite easily with synthetic oil and a turbo timer. The coking refered to really is something that happens with dino oils, but if you go synth with a higher flash point, and especially if you keep the oil running just a bit after the car stops, it will cool the bearings just fine and not have problems of coking on the bearings. I've seen large numbers of oil cooled turbos run well past the 100k mile mark with no bearing issues.

Alan C.

Polymer quenches are far superior to water in heat transfer. If youd drop something substantially hotter than 100C into water the first thing which happens is a water vapor/steam jacket which will insulate the part from the water. The polymers can withstand higher temps before the same problem arrises.

I beleive Tim was comparing air to water in the case he cited. Just left the air part out.

Alan

jason952

[quote]Originally posted by Danno:
<strong>. In fact, last August when I was at Willow Springs, it was 115-degrees out! My water-temp never went above 2/3rds but my oil-temp was so high, I only had 3.5-bar of oil-pressure from the thinned-out oil.</strong><hr></blockquote>

Is that at full throttle? what weight? thx Danno,

Jason

GrantG

Yeah, my oil got so hot that I was seeing under 3 bar at 6k revs. I just bought a Mocal kit from Terry Morris at KISS and hope to try it today for the first time at the track.

GrantG

BTW, I use Mobil 1 15W-50...

GrantG

Just got back from the track and the temp is down and the oil pressure is up with the oil cooler from Terry Morris at KISS. It requires pulling out the driver-side driving light (replaceable), but it's very worth it!

Water temp now doesn't go higher than top white line maxxed out at the track for many laps and oil pressure stays above 3.5bar at high revs. Before it would get to the red and go below 3 bar...