Oil cooler/temp question

[Doug Hillary]

Hi,
as an example; (all temps +/-2C)
Porsche all alloy 5ltr 32v V8 - 320hp (coolant cooled)
Front engined, torque tube to rear transaxle

Coolant
Radiator is heat sink - coolant thermostat operates on bottom hose. Thermostat cracks at 83C and is fully open at 98C (Initial engine warning at 118C, final warning at 120C)

Oil cooler - heat exchanger type in coolest part of radiator. Oil thermostat opens at 87C and is fully open at 91C)

Air flow (flaps) - these are temperature regulated via a variety of inputs. Main input (others are A/c, engine heat, ATF temp)is sensed at coolest part of radiator. This activates flaps to 30% open at 79C. They are sensed and progressively opened at "break" levels up to fully open at 85C via main input. Under body ducted shields are used

Fans (2)- variable speed fans are used. these activate initially at 79C and are at maximum speed above 95C

Note: all systems operate in reverse (from the input matrix) as temperatures decrease

Over many years of testing the maximum recorded temperatures are;
oil = 90C into oil cooler
coolant = 92C

Coolant average = 86C

Core engine temp average is = 89C (vee)

Mostly my air flaps are closed and fans off or at 30% open when the ambient is above about 33C
They are rarely fully open on the open road even at temps around 38-40C and at speeds up to 200km/h+

In very cold conditions the flaps are closed and fans off of course and the engine maintains a "next to zero" air flow regime. In fact I believe in some condition they struggle to get to FI sensor and other actuator sensor temps and this is why the engine has this sophistication

This indicates a very stable cooling system as I live in the Tropics and operate the car in temperatures ranging from -5C to 40C+.
Most of my driving is fast and open road

I believe that this engine has almost perfect temperature regulation

Regards
Doug

 

[Gary Allan]

Doug, you've got an advanced and well balanced system. A bit sophisticated for the aftermarket adaption crowd ..but one surely to admire for "thinking of everything".

Hmm...I wonder if a "shutter-stat" from a big rig can be downsized for use in an appropriately altered auto

 

[jdmboy]

Mmy coolant goes up alright. The problem is the 4.5" think intercooler in front of the radiator.In NC for example but in AZ it makes the cooling system "cooling challenged" despite the double capacity Australian aliminum radiator. You can see in top of it the post above. Really it is only an issue in the summer months but the oil cooler has seemed to cure it.

There is a factory oil to coolant heat exchanger that was contributing to the problem. When the oil got hot the coolant got hot and the radiator has a 4.5" thick intercooler in front of it. Got to cool that 400F turbo charged air. The poor cooling system cold not shed fast enough.

Even at 75mph on the highway it was a problem when the outside temps were 110F+. The oil cooler most certianly fixed the oil and coolant temps. 225hp per litre is tough on a motor. I can spike my oil temps with 5th gear pulls on the highway. Just watch the needle go up really.

The hot is taken care of and the 85C oil thermostat should take care of the colder side. My 6 speed has an oil pump in it so I am going to plumg it to the same core on the other side of the car with a thermostat as well. I just need to get an idea of normal gearbox oil temps to spec the thermostat for that modification correctly.

To get an idea of the Turbo Intercooler size....

[ July 31, 2005, 12:02 AM: Message edited by: jdmboy ]

 

[Doug Hillary]

Hi,
I cannot give you accurate gearbox temp data that is meaningful for your application

I can tell you that synthetic gear oils will tolerate up to around 300F intermittently with ease.
My trucks (Class 8 500hp 42.5t) run with an average at 86C and a high of 120C

I use Castrol Syntrax 75w-90 (GL5) as IMHO the Castrol range of gear oils are amongst the best around - if not the very best

I hope this "ramble on" helps a little
Regards
Doug

 

[Gary Allan]

One intense machine. That oil/coolant heat exchanger will now help your rad shunt some heat to the oil cooler. If you still have coolant issues, you may consider an even bigger oil/coolant exchanger to further enhance using your oil as a cooling medium.

I couldn't find one reference to a recommended gear oil temp anywhere on the net. Many references to coolers ..but none pointed to a preferred temp. I don't imagine, given your ambient temp, that a thermostat would be required ..unless you decided to go with a 75w-140 GL-5 which has a 100C visc of around 25 Cst ..compared to the 75w-90 which weighs in at around 15 cst (90 weight hypoid is a "40 weight")

 

[Doug Hillary]

Hi,
XJ650 - SAAB also had the roller shutter on both the 3 and 4 cyl engines. The problem was that people forgot to let them down and overheating resulted. They also caused excessive under bonnet temperatures and "vapour lock" under some conditions
IIRC a couple of rear engined Russian cars had radiator blinds too (Zaphrojet and ?)

I think the availability of dependable eletronics and light materials make air flow controls a real possibility for an enterprising after market supplier. They are especially effective in cold conditions below about 5C and where there is a significant chill factor

In the case of the Porsche, when the flaps are shut or 30% open some air is deflected to the dual cold air intakes at the top of the radiator
This enables an air flow over the hottest engine parts and cold intake air too

Regards
Doug

 

[jdmboy]

Hmm, yes I wonder what the Rally application uses. It has real small lines and a real small core upo front. Perhaps 1 qt total. I suspect is uses no thermostat.


Just curious, does one ever have high lead and then switch oil and the symptom goes away? I mean does it ever really pan out to be viscosity related or is one high lead always high lead?

 

[XS650]

quote:

---

Originally posted by Gary Allan:
Doug, you've got an advanced and well balanced system. A bit sophisticated for the aftermarket adaption crowd ..but one surely to admire for "thinking of everything".

Hmm...I wonder if a "shutter-stat" from a big rig can be downsized for use in an appropriately altered auto

---

How about a poor mans version. In the 1950s Volvo has something that looked like a roller window shade in front of the radiator. IIRC, the driver could operate in manually from inside the car.

 

[jdmboy]

sounde like a good idea. Who is Terry, how do I contact him and what do I ask for?

 

[bulwnkl]

Look in the Site Sponsors section for Dyson Analysis. Terry is worth his money.

 

[Gary Allan]

quote:

---

Just curious, does one ever have high lead and then switch oil and the symptom goes away?

---

Well, I've never had a Pb issue, but visc can solve one dimensional wear. The rest of your indicators are normal considering (and even in spite of) your driving situation. You may not have a visc issue with your old oil selection now that you have your oil temp under control

You should really consult Terry. For a few $ added to the next UOA he'll probably short cut a lot of playing around to lock your Pb issue down.

 

[jdmboy]

Thermostat arrived today. It is an 80C not 85C unit. The oil tends to run 90C in the afternoon and 80C when it is really cool out with no thermostat and open oil cooler lines. Coolant Thermostat is 73C.

Send the oil thermostat back for an 85C unit or use the 80C unit I got?

 

[Gary Allan]

I see what you're asking. Is it worth putting in the thermostat for ...nothing? You'll still get warmed up faster with the thermostat by taking the oil rad out of the loop for that period. I still think that your 73C thermostat is doing more harm than good ..unless you never actually have a static condition that it can regulate @ 73C. If that's the case ..then you're just briefly (whatever duration briefly is) delaying warm up to whatever typical temp you see when you're not hammering it (however little you have to hammer it to get it off of 73C).

If this were mine, and given the limitations of the cooling rad, I'd put a 85C coolant stat and really put some research into getting a bigger oil/coolant heat exchanger (in addition to the one already installed). This would allow you to shunt more coolant heat to the oil ..and to the oil radiator ..effectively expanding your coolant capacity. Your current oil rad keeps your oil temp between 80-90C. Well under control. If your coolant exceeds that temp ..then there's "room" for excess btu's in the oil if you can shunt them to it. You can get them to work in tandem to carry the thermal loading of the rad. You've just got to build a big enough bridge between them

If you've got 6-8" of fairly straight upper or lower (or both) rad hose ... it would fit. I would plumb them post oil thermostat - in line with the oil cooler rad. This will shunt more excess coolant btu's to the system that has the most capacity for it. I'd also research the suitability of a PG coolant for this application to avoid localized boiling/cavitation. Since you run hot anyway, you might as well have something that doesn't boil until about 375F. You don't have issues of it getting too viscous in cooler weather. It will, however, probably have you running at a higher temp than an EG alternative.


The shorter answer is send it back for an 85C thermostat ..and really think hard about swapping out the coolant thermostat for an 85C as well.

Good luck!