Why does TDI have oil cooler?

[Waldek Walrus]

I was asked why does the TDI, that is so cold blooded that it is hard to warm up on a cool day, need an oil cooler. Seeing that I felt rather full of the blarney at the moment I said it was because the oil is used to cool the piston crowns to keep them from burning through when running at high load with full turbo boost. I have found out the hard way that the oil gets REALLY hot in the TDI despite how cool it seems to run otherwise. Was my answer unadulterated BS? There has to be a real reason...

 

[DPM]

It's a heat exchanger- it can heat as well as cool the oil...

 

[Waldek Walrus]

It's a heat exchanger- it can heat as well as cool the oil...

I thought that when I had an IDI diesel long before turbo and it had an oil cooler (heat exchanger). I shared the idea that it was needed to heat the oil with an engineer that used to work for International Harvester on R&D for their tractor engines and he looked at me so much as to say "What rock did you crawl out from under?" But he never did say why there would be so much heat dumped into the oil.

 

[compu_85]

Actually, the old IDI turbo diesels (and the automatic NA ones) got the EXACT same oil cooler as the TDIs until the end of the ALH!

-Jason

 

[BKmetz]

Don't forget most turbo-diesels of any make have oil cooled pistons. This can heat up the oil considerably more than the coolant temperature.

 

[Waldek Walrus]

Don't forget most turbo-diesels of any make have oil cooled pistons. This can heat up the oil considerably more than the coolant temperature.

Good That's what I peddled to the guy who was asking me, so it wasn't total bean soup.

 

[compu_85]

Also, the turbo is cooled by the oil. In fact, I think the turbo's oil feed line connects right after the cooler.

-Jason

 

[DrSmile]

Because TDIs are hot and you're cool to own one?

 

[lupin..the..3rd]

Also, the turbo is cooled by the oil. In fact, I think the turbo's oil feed line connects right after the cooler.

1. The turbo on many newer cars is watercooled. On our TDI's, it's oil cooled. So the turbocharger adds significant heat load to the oil.

2. The oil cooler is actually a heat exchanger. The coolant reaches operating temperature much sooner than the oil does. This heat exchanger transfers heat from the coolant to the oil to bring the oil up to OT sooner. Once at OT, the heat exchanger then takes heat from the oil and transfers it to the coolant where it's dissipated through the radiator.

A very handy little device really. ALL tdi's, heavily modded or bone-stock can benefit from a heat exchanger upgrade. Brings the engine up to OT quicker for less engine wear, and maintains OT better in hot weather. A win-win scenario. (See my sig for the V6 oil cooler upgrade).

 

[tongsli]

I installed the oil cooler to the right.

 

[oEo]

Tongsli,

How much more oil do you add? Or, what is your total capacity now?

Thanks
-Tony

 

[weedeater]

Someone a number of years back put a temp sensor in the oil pan and was surprised to see how hot the oil gets after a while. Yet another reason to use synthetic.

So a bigger cooler is a good thing.

 

[tongsli]

Tongsli,

How much more oil do you add? Or, what is your total capacity now?

Thanks
-Tony

I have no idea. Not enough for me to measure and tell you a number/figure.

 

[rotarykid]

Our engines also have oil sprayers to remove heat from the pistons which adds much heat to the oil that must be removed along with the heat the turbocharger adds to the oil system .

With the above the oil gets at least 100+* F-( 350 - just under 400 * F are possible ) under load above the water temp is possible-( I've seen over 350* F on a heat gun ) so much heat is removed in the heat exchanger system .

 

[Waldek Walrus]

Our engines also have oil sprayers to remove heat from the pistons which adds much heat to the oil that must be removed along with the heat the turbocharger adds to the oil system .

With the above the oil gets at least 100+* F-( 350 - just under 400 * F are possible ) under load above the water temp is possible-( I've seen over 350* F on a heat gun ) so much heat is removed in the heat exchanger system .

This seems a good summary of the situation. I checked the oil after the Beetle sat in a convenience store parking lot five minutes after driving up a mountain (several miles steep upgrade making the TDI run with lots of boost). I can personally attest that the business end of the dipstick was VERY, VERY HOT. The 350 F plus quoted above is entirely possible.

Thanks all for furthering my TDI education

 

[Dimitri16V]

that is the only flaw of the belly pan. It does not allow any air stream to cool off the oil pan and oil cooler. the aluminum pan would drop the oil temps atleast 20F on the highway without the belly pan in place.

 

[burpod]

but wouldn't then you be getting more drag? hence inreasing EGTs?

 

[david_594]

that is the only flaw of the belly pan. It does not allow any air stream to cool off the oil pan and oil cooler. the aluminum pan would drop the oil temps atleast 20F on the highway without the belly pan in place.

Usually when something is intentially designed in a specific manner its called a feature and not a design flaw. If vw felt the oil needed supplemental air cooling via the oil pan, they would have used an oil pan specifically designed for it.

 

[Dimitri16V]

the belly pan was put there to reduce noise and make TDIs more appealing to diesel haters. It increases underhood temps, a good thing for faster warmup in winter but not if you live in areas with high temps all yr around.
It's a compromise.

 

[Bob_Fout]

Oh it doesn't keep dirt and water off front getting into the engine bay?

 

[karlaudi]

the belly pan was put there to reduce noise and make TDIs more appealing to diesel haters. It increases underhood temps, a good thing for faster warmup in winter but not if you live in areas with high temps all yr around.
It's a compromise.

Well, at least on my A4 and Golf TDi the belly pan acts an aerodynamic device in smoothing the airflow under the car. Cooling air enters above and below the bumpers on both cars and exits out the gap between the belly pan and the underbody. I would guess that the airflow flowing under the car, especially at the point about where the pan ends, is at a lower pressure than the air flowing through the engine compartment, due to an induced venturi effect, and therefore improved air flow through the engine compartment occurs, by the "vacuum effect" of the negative pressure higher velocity airflow running under the car, while at the same time reducing turbulence at the lead end of the car as it passes through the air.

In fact, the A4, with a much longer belly pan than my TDi, features two NACA ducts to deliver addition high velocity air, from the under car airflow, to enter between the pan and the body to around the transaxle differential and exhaust system and "scavenge" this area.

My normally aspirated 1988 Audi type 89 80 quattro with a 2.3L 5-cylinder had similar cooling ducts in its belly pan, as I recall.

 

[OilGuy]

Don't TDI's run cooler (coolant temp) than the avg gasser as well?

 

[oilhammer]

FWIW, many modern cars have oil piston squirters. All newer Volkswagen engines, gas or diesel, turbo or not, have them.

The oil cooler is also an oil warmer, since it helps the faster-warming coolant get the slower-warming oil up to temp. Hot oil flows and lubes better than cold oil.

Oil temps are regulated by the oil/coolant heat exchanger. Volkswagens run high oil temps, which is good. Makes sure all the moisture is boiled away and taken out the crankcase via the breather system.

If you have an oil temp gauge, you'll notice the oil temps stay pretty constant once up to temp...there is not any variance really, just like the coolant. The thermostat and fan(s) regulate the temperature quite well.

A larger oil cooler will only allow a faster transfer between the two, it will not "lower" the oil temps really. Just makes it more efficient since it can more easily transfer the cold/heat.

I have experimented with oil coolers in various applications, including VW diesels. On an old slightly modded '81 diesel Caddy I had, the addition of the factory style oil-to-coolant cooler did make the oil come up to temp faster in cold weather (much faster, actually) but had very little effect when hot as to reducing the oil temps. It did reduce the oil temps more in summer heat when I ran the engine with no thermostat.

What drastically reduced the oil temps on that engine was an oil-to-air cooler, which Volkswagen used on some water cooled cars. It was essentially one of the later air-cooled engine's oil cooler with an adapter and lines to go to the special factory oil filter mount. The only cars we would have seen these on here in the states were some 5000 turbos. They even had a little thermostat built in to the adapter. It would easily scrub 30 to 40 degrees off the oil temps on hot summer days on the highway at speed.

But in the end, the best (ideal) oil temps are just over 100 C (212 F). Hot enough to boil water into vapor, but not nearly hot enough to boil the oil. The air cooled engines routinely tag 250 F oil temps (I've had my air-cooled Vanagon up to 270 F a few times when towing). So the regulated temps in the modern Volkswagens is plenty cool.

 

[Keith_J]

oilhammer has it right. A larger oil cooler/heater will only help when the oil temps are very high. The stock cooler works well with most dirving conditions.

The belly pan is used for aerodynamic effects as well as sound control.

Engine temp warm-up is greatly enhanced via EGR and additional glop plugs. Only slightly increased via shrouds and then only in very cold conditions.

Oil-cooled pistons are common to VAG engines. My Audi 4000 had them some 20 years ago.

 

[rotarykid]

What drastically reduced the oil temps on that engine was an oil-to-air cooler, which Volkswagen used on some water cooled cars. It was essentially one of the later air-cooled engine's oil cooler with an adapter and lines to go to the special factory oil filter mount. The only cars we would have seen these on here in the states were some 5000 turbos. They even had a little thermostat built in to the adapter. It would easily scrub 30 to 40 degrees off the oil temps on hot summer days on the highway at speed.

I have a couple of those Audi oil coolers in a box somewhere . Along with a few of those heavy duty turbos , intakes & exhaust manifolds from that erra .

On my Audi 5000 TDs in extreme heat high oil & water temps were a problem in high speed high altitude driving as was stated in the owners manual even with the extra cooling given from that oil cooler .

A little background , In the late 80s I learned that in Europe VWAG was inter cooling the IDI TDs to get more power & mpgs out of them . So I applied this knowledge to the IDI TDs I owned .

On my 5000 TDs , I owned 3 of them over the years I modified the intake and made a crude inter cooler out of hose & pipe . It was unbelievable how much difference it made in oil & water temps along with available power .

After seeing this result I did the same to my Quantum's & Jettas TDs . Was able to put more power out and increased mpgs without causing failures .

Now we all have inter coolers & oil coolers so this has been taken far to this point . The newest models of the TDI have inter cooler fans . The only this that might make a real dent in oil temps is an aux. oil / air exchanger like Audi used just as Oilhammer stated .

On our engines being completely enclosed top & bottom , our cars are designed for the best aerodynamics air flow around the car & under the hood .

So VW uses these panels that enclose the engine bay to help funnel cooling air through the engine bay . So if you remove any part of this air flow ducted designed system you can disrupt the entire cooling air flow systems efficiency leading to a possible overheat in extreme heat under high load .

I saw many of the older Audi diesels with the radiators air duct & belly pans missing that were always overheating and the owners had no clue why . I would fabricate the missing panels and install them . After this one change the overheating issue would go away almost every time .

 

[tdisky]

Thanks all, for the great thread; I learned something at lunch today!

Hey rotarykid, I take it that's an RX-2 in your avatar? I know this is off-topic, but it brings back great memories of my '71, which I loved nearly as much as my TDI. Once you hit 3000 rpm in 2nd gear, you're gone. As is your spare cash; 16 mpg with the same driving style as I use in my 47 mpg TDI. Both are lots of fun.

 

[rotarykid]

Thanks all, for the great thread; I learned something at lunch today!

Hey rotarykid, I take it that's an RX-2 in your avatar? I know this is off-topic, but it brings back great memories of my '71, which I loved nearly as much as my TDI. Once you hit 3000 rpm in 2nd gear, you're gone. As is your spare cash; 16 mpg with the same driving style as I use in my 47 mpg TDI. Both are lots of fun.

Rx4

 

[WW_VRS]

That said when cruising at 110mph (yes I know, a tad fast) I would imagine having additional oil cooling wouldn't hurt (thermostatically controlled of course). I've got a PD130 running at 201bhp right now, and it will be tuned up to about 250ish bhp at some stage (injector upgrade still to be done, I've got them but not had time). Also I have propane, albeit turned off right now.

The extra heat load that puts on the engine, plus the detonation damage I had when the cooling system failed on my car, makes me want to be able to take the heat out more quickly. It's most important when you are driving fast (plenty of air cooling the radiator) and you suddenly have to slow down (traffic jam), loads of residual heat to get rid of, and then the heat exchanger isn't all that great...