Louis19's Build Thread

**sambb** · 26-04-2018, 11:37 AM

and the sandwich plate, that'll be a thermostated type yeah? I'm guessing you'll ditch the water heat exchanger and straight pipe that section yeah?

**louis19** · 26-04-2018, 04:04 PM

Originally Posted by sambb

and the sandwich plate, that'll be a thermostated type yeah? I'm guessing you'll ditch the water heat exchanger and straight pipe that section yeah?

Yes and yes. 80 degree thermostat and I will remove the heat exchanger completely and plumb the two coolant lines together.

**sambb** · 26-04-2018, 06:15 PM

were your oil/water temps getting a bit out of hand or just a precaution?

**louis19** · 26-04-2018, 08:58 PM

Originally Posted by sambb

were your oil/water temps getting a bit out of hand or just a precaution?

Bit of both to be honest. Being that we run the heat exchanger factory, once on track and hot it appeared as though all the exchanger was doing was putting extra load onto the radiator trying to cool both fluids and just transferring heat between each fluid.

Separating the fluids should take a lot of work off the radiator, having their own independent coolers to do their thing

**sambb** · 27-04-2018, 09:49 AM

yep it might work well on the street in cool climates but I think once your on the track the water and oil temps just drag each other up to which ever one is the highest via the heat exchanger. I'd be curious to see what happens just by ditching the exchanger and not even running an oil cooler. I have a big capacity baffled/door race sump and when that goes in I was thinking I might see whether the separation of oil and water and the extra oil capacity might be enough.

**Sydneykid** · 27-04-2018, 11:55 AM

The much discussed oil temp versus water temp debate. Oil fundamentally has to run at or slightly above 100 degrees C, this is to "boil off" any moisture (water) in the oil. If the oil temp is always less than 100 degrees C then the water will stay trapped which is not good for lubrication. It's actually a bit worse than that as water has a higher specific gravity than oil and as such it sits in the bottom of the oil pan, where the oil pump pickup is.

Within the same thermal thoughts, water boils at 100 degrees C at atmospheric pressure. If we run, say, a 22 psi radiator cap (that's high pressure) then the water will boil at around 125 degrees C. As a comparison F1 cars run at a regs mandated 55 psi which equates to 150 degrees water boiling point. From memory the standard VW caps are around 15 psi, good for around 120 degrees C.

What I always look for is to get the oil temp up from engine start fairly quickly, that's where a water to oil heat exchanger is very effective as they come up in temperature together, faster. On engines with dry sump systems we even run a heater in the tank. In NASCAR they like to run the engine's water temp at around 85 degrees C, they make more horsepower. Over that and they loose power.

My rules of thumb, keep the water below 90 degrees C, make sure the oil gets to 100 degrees C fast but doesn't go much over 125 degrees C. With that in mind I'm not big fan of having a 125 degree C oil cooler directly in front of a radiator that I want to have an exit temp of 80 to 90 degrees. Separating the air flows is worth the extra effort.

Cheers
Gary

**sambb** · 27-04-2018, 08:17 PM

Is it possible to run a water/oil heat exchanger then yet still have a thermostated oil line to the cooler?

**louis19** · 29-04-2018, 09:11 AM

Thanks for the post Gary, that's helpful information and something I will keep in mind when monitoring how the car responds to the new setup.

Sam, yes you can run the factory heat exchanger with the sandwich plate stacked below it, and there is a few others that have done this around the world however on Polo's I think you would struggle for room unless you ran a shorter oil filter. I think if you tried to stack them and ran the factory length oil filter, it would be extremely close if not hitting the plastics on the back of the radiator.

**sambb** · 29-04-2018, 10:01 AM

Ok well that would be best of both worlds I guess. Fast warm up but with the cooler when its needed. I suppose you could stack the exchanger and thermostat and run a remote oil filter.