mazda skyactiv vs hyundai theta engine

**GTi** · August 22nd, 2015 12:44 AM

I believe many premature turbo failures are because of neglecting to let it idle for a bit before engine shutoff after hard driving. This must've been the cause of numerous problems with Accent CRDi cabs and ignorant cab drivers, the reason why there are so few Accent cabs running around nowadays despite them being relatively new.

Hyundai CRDi's are actually quite successful. Many Starex CRDi's are still running around, most likely with high mileages already, and they are one of the first mainstream CRDi's sold here, besides the problematic Isuzu 4JX1. It hasn't become notorious for any particular problem that I know of besides normal wear and tear or abuse and neglect.

**Jun aka Pekto** · August 22nd, 2015 01:37 AM

Originally Posted by bloowolf

For one, the manufacturer's manual states to avoid idling for more than 5 minutes, which, I think is impossible in the Philippines. There are also the drivers who keep their engines running for 30 minutes at least, just to keep the cabin cool for the boss & for themselves. Exhaust gases still pass through the turbo though the spindle isn't spinning, probably cooking the residual oil. Anyways, the manual says that a 20 sec warm up & a minute cool down is sufficient for a Hyundai, maybe different for a Mitsu.

Hyundai haven't done turbos in their gasoline cars that long. Most likely, they use modern turbos with both oil and water cooling. The water cooling allows the turbo temperatures to drop faster, making coking less of a danger. Mine (both Mitsu and older Garrett turbos) was older and oil-cooled only with coking always a danger.

As for excessive idling. I would think it would be more of a problem with deposits building up in the engine itself rather than the turbo. I haven't had a turbo car for a long time. So, I could be wrong.

**bloowolf** · August 22nd, 2015 08:30 AM

Originally Posted by Jun aka Pekto

Hyundai haven't done turbos in their gasoline cars that long. Most likely, they use modern turbos with both oil and water cooling. The water cooling allows the turbo temperatures to drop faster, making coking less of a danger. Mine (both Mitsu and older Garrett turbos) was older and oil-cooled only with coking always a danger.

As for excessive idling. I would think it would be more of a problem with deposits building up in the engine itself rather than the turbo. I haven't had a turbo car for a long time. So, I could be wrong.

I think it was in YouTube videos I heard this from, but they say that during excessive idling, the oil stops flowing into the turbocharger since it is not spinning anymore. With excessive heat buildup & without adequate cooling, residual oil gets baked (combined with deposits), causing the toothpick sized spindle to fail eventually.

**bloowolf** · August 22nd, 2015 12:43 PM

BTT: this is an engine that I hope makes it into production: Hyundai's Experimental Gas Engine Runs Without Spark Plugs ? Feature ? Car and Driver

**Jun aka Pekto** · August 22nd, 2015 08:21 PM

Originally Posted by bloowolf

I think it was in YouTube videos I heard this from, but they say that during excessive idling, the oil stops flowing into the turbocharger since it is not spinning anymore. With excessive heat buildup & without adequate cooling, residual oil gets baked (combined with deposits), causing the toothpick sized spindle to fail eventually.

With oil-cooled turbos, I think the engine oil (that is used to cool the turbo bearings) continues to flow so long as the engine is running, even at idle. The oil stops flowing when the engine is shut off which then cooks inside the turbo bearings. The turbos get really hot. One night, a few years ago, I went out driving with a friend who had a WRX. He did some mountain climbing with it. At a rest stop, he popped open the hood and the turbo was glowing a dim red in the dark. That's how hot it was. If you turned the engine off right at that moment, the oil would cook really fast and mess up the turbo bearings.

The excessive idle part would build up gunk and deposits in the engine (not the turbo itself) which is also bad for the turbo should they come loose and get in the exhaust. But, you could probably get rid of it by doing a speed run. That's why once in a while, I used to accelerate my Plymouth Laser to 130 mph and get rid of all that gunk.

Edit:

Having a turbo car in idle and moving with cruise control enabled would be very similar in that the turbo boost would be zero and the engine is running in both situations. The only differences concern the transmission and the higher engine RPMs with the car in motion. The negatives with excessive idling has a direct effect on the engine but not the turbo itself.

**yebo** · August 22nd, 2015 09:17 PM

The only 2 ways to "cook" a turbo are 1.) to shut off the engine while the turbo is still hot (no cool down) and 2.) to immediately shut off the engine after pressing the accelerator pedal down, like what old school drivers used to do (vrooom vrooom then shut off engine). The 1st is obvious, the cooling oil stops flowing while the turbo is still hot, causing the oil to "cook" in the bearing. This causes "varnishing" of the oil, leading to smaller tolerances which eventually lead to oil starvation. The second, this causes the turbo to spool up, then when the engine is immediately shut off the turbo is still turning at thousands of rpm and there is no longer any oil flow to lubricate it. Result is a "cooked" bearing.

**glenn manikis** · August 22nd, 2015 10:00 PM

All our gensets have a cool down period of a maximum of 2mins. And out of tens of thousand of units sold only 2-3 was prematurely replaced... Kahit na nga units that are 30years old or units that are made in China... Kahit pa hindi regularly maintained... Lifetime tumatagal...
Sa experienced din namin the moment na nagleak na yung turbo Kahit ilan beses Ka pa magpalit ng repair kit.. Paulit ulit na masisira.. It's suggested na magpalit nalang ng bagong turbo....

**weisshorn** · August 23rd, 2015 10:11 PM

oil starvation or complete stoppage of oil flow will result to early break down of the turbo charger. kahit repair kit replacement/repair basta maayos at "balance" ang rotor assy hindi basta basta mag oil leak yan assuming of course na ang casing is good and the repair was done right.

**Jun aka Pekto** · September 1st, 2015 12:32 AM

Originally Posted by yebo

The only 2 ways to "cook" a turbo are 1.) to shut off the engine while the turbo is still hot (no cool down) and 2.) to immediately shut off the engine after pressing the accelerator pedal down, like what old school drivers used to do (vrooom vrooom then shut off engine). The 1st is obvious, the cooling oil stops flowing while the turbo is still hot, causing the oil to "cook" in the bearing. This causes "varnishing" of the oil, leading to smaller tolerances which eventually lead to oil starvation. The second, this causes the turbo to spool up, then when the engine is immediately shut off the turbo is still turning at thousands of rpm and there is no longer any oil flow to lubricate it. Result is a "cooked" bearing.

That's what I thought. I saw turbo engines idle for long periods without ill effect.

I did the same with my gasoline Mitsu 4G63-T engine, especially during cold winters when it took 10 minutes idling just to bring the engine RPMs down to normal. It took even longer for the temperature gauge needle to start moving which could take another 5-10 minutes of idling. I'm not 100% sure because I usually started the car and then ran back inside the house. Brrrr.

But, I think we're in the same page with regards to the engine shutdown part where the greatest risk for turbos is at.