Turbocharger Cooling -- Oil and Coolant
11-15-2010, 02:58 PM
#1
haole kama'a-ina
Thread Starter
Turbocharger Cooling -- Oil and Coolant
There's been some recent questions about how the turbocharger is cooled; as it regards various oil choices.
It's cooled by both oil and coolant.
The turbocharger may spin at about 10,000 rpm at low engine speed and up to about 100,000 rpm at full throttle. Engine exhaust spins the turbine spool which it turn spins the compressor spool, which delivers pressurized air to the intake. That generates extreme heat in the bearings between the turbine and compressor.
In the RDX, the bearings run in an oil bath supplied by a line at the top of the bearing case. The pressurized oil runs through the bearing case and out a return line at the bottom. This is how most turbochargers are lubricated and cooled. During operation the oil carries away heat as it passes through the bearing case.
The problem arises after shutdown. The bearing case is extremely hot and the oil is no longer flowing. Oil in the bearing case is cooked and burns or "cokes" onto the turbo shaft and bearings. Burned oil deposits interfere with bearing operation and can block the oil supply line. A turbocharger running without oil will burn up faster than Rosie O'Donnell can elbow her way to the front of the Dairy Queen line.
So a Honda approved HTO-06 synthetic oil is critical to protect the turbocharger. Mobil 1, Pennzoil Platinum, etc can withstand the intense heat without coking the turbo shaft and bearings. It is equally as critical to maintain the oil level and change it on schedule.
Honda's first turbocharger is also cooled by engine coolant. The bearing case is surrounded by a water jacket. Pressurized coolant flows around the oil-filled bearing case, carrying away heat. More importantly, when the engine is shut down and oil stops flowing, the coolant continues to flow through the bearing case water jacket. The system is cleverly designed to move coolant by convection through the turbocharger as long as a heat imbalance exists in the cooling system -- no after-run coolant pumps are needed. RDX owners should have a gallon of Honda Type 2 pre-mixed coolant at home and keep the reservior level between the lines.
In the past its always been advisable to cool a turbocharger at idle before shutting down. With their water convection cooling, Honda says this is not needed. However, it's still a good practice to run the last mile easy and off boost before shutting down.
The picture below shows the turbocharger bearings located between the two spools and its oil and water cooling ports.
It's cooled by both oil and coolant.
The turbocharger may spin at about 10,000 rpm at low engine speed and up to about 100,000 rpm at full throttle. Engine exhaust spins the turbine spool which it turn spins the compressor spool, which delivers pressurized air to the intake. That generates extreme heat in the bearings between the turbine and compressor.
In the RDX, the bearings run in an oil bath supplied by a line at the top of the bearing case. The pressurized oil runs through the bearing case and out a return line at the bottom. This is how most turbochargers are lubricated and cooled. During operation the oil carries away heat as it passes through the bearing case.
The problem arises after shutdown. The bearing case is extremely hot and the oil is no longer flowing. Oil in the bearing case is cooked and burns or "cokes" onto the turbo shaft and bearings. Burned oil deposits interfere with bearing operation and can block the oil supply line. A turbocharger running without oil will burn up faster than Rosie O'Donnell can elbow her way to the front of the Dairy Queen line.
So a Honda approved HTO-06 synthetic oil is critical to protect the turbocharger. Mobil 1, Pennzoil Platinum, etc can withstand the intense heat without coking the turbo shaft and bearings. It is equally as critical to maintain the oil level and change it on schedule.
Honda's first turbocharger is also cooled by engine coolant. The bearing case is surrounded by a water jacket. Pressurized coolant flows around the oil-filled bearing case, carrying away heat. More importantly, when the engine is shut down and oil stops flowing, the coolant continues to flow through the bearing case water jacket. The system is cleverly designed to move coolant by convection through the turbocharger as long as a heat imbalance exists in the cooling system -- no after-run coolant pumps are needed. RDX owners should have a gallon of Honda Type 2 pre-mixed coolant at home and keep the reservior level between the lines.
In the past its always been advisable to cool a turbocharger at idle before shutting down. With their water convection cooling, Honda says this is not needed. However, it's still a good practice to run the last mile easy and off boost before shutting down.
The picture below shows the turbocharger bearings located between the two spools and its oil and water cooling ports.
Last edited by 737 Jock; 11-15-2010 at 03:10 PM.
11-15-2010, 03:04 PM
#2
haole kama'a-ina
Thread Starter
In all probability, high-end boutique oils not on the HTO-06 list will serve fine, although they could become an issue over a warranty claim.
11-17-2010, 05:28 PM
#7
Senior Moderator
Thanks for the info. I've been trying to let it cool down before shutting off. I also turn off the heat or A/C before turning off the car. Not sure if that does anything, but I feel like it must be less stress on the system upon start-up. I'm also paranoid about the A/C after my 04 TSX. 
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11-17-2010, 05:53 PM
#8
def less strain on start up - be sure that in the winter, you are starting up with as little draw as possible on the battery - lights on, heat on, seat warmer on; if left on from the night before - will make for much harder starts in the cold weather.
02-10-2011, 02:29 AM
#10
Do you know if those turbo bearings are sleeve type running under pressure (plain bearings like in the engine), or are they some type of ball bearings, like Nissan intro'd all the way back in the '80s?
Any idea of the brand of RDX turbo, which would make it easier to find some technical data on the turbo?
I have been looking for a couple of hours now, but I am not the greatest at using Google to its potential. Thanks.
02-10-2011, 11:38 PM
#11
haole kama'a-ina
Thread Starter
Well, I don't know.
But because of Honda's emphasis on reliability, it is less likely that they would use journal (sleeve) bearings, due to their high dependance on quality oil, proper flow, etc.
The RDX turbo oil feed pipe has a banjo bolt (exiting engine) that appears to serve as a flow restrictor. This would usually indicate the presence of ball bearings, and as ball bearings have a much higher tolerance for oil mismanagement, I'd tend to think that's how Honda would go.
They could even be ceramic.......nah, probably not, as ceramic is pricey and less likely to use water cooling.
But because of Honda's emphasis on reliability, it is less likely that they would use journal (sleeve) bearings, due to their high dependance on quality oil, proper flow, etc.
The RDX turbo oil feed pipe has a banjo bolt (exiting engine) that appears to serve as a flow restrictor. This would usually indicate the presence of ball bearings, and as ball bearings have a much higher tolerance for oil mismanagement, I'd tend to think that's how Honda would go.
They could even be ceramic.......nah, probably not, as ceramic is pricey and less likely to use water cooling.
Last edited by 737 Jock; 02-10-2011 at 11:41 PM.
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