Sep 08, 2021 Chris Kambouris, TurboDirect SA, Turbocharger
Looking after your Turbo powered vehicle fitted with a Stop/Start feature or the latest technology
Looking after your Turbo powered vehicle fitted with a Stop/Start feature or the latest technology that they say does not need to be cooled down or warmed up.
This is not correct, and we would not recommend it says TurboDirect SA to even the latest models. Several car and vehicle owners came back to us on cars fitted with the auto stop start system some being owners of some of the latest innovative turbo models, asking how the daily turbo care routine applies to them with the day-to-day driving.
“So, let me comment on this and shed light on the subject,” said Chris Kambouris founder, owner, and MD of TurboDirect SA. Firstly, I neglected to mention this “feature” in the original article, every vehicle manufacturer is different, and many have added external components to compliment and assist this “feature” in preventing damage to occur to the turbocharger and/or Battery and starter motor. Let me start on the starter motor side, from experience and direct involvement with many of the OEM vehicle workshops, and their technical staff, we have learned that there has certainly been an increase in starter motor failures since the original inception of the Start/Stop “feature” - some of these are covered under warranty, and the warranty replacement over time has been found to have had an upgraded starter motor and/or battery installed, unbeknown to the client. Other vehicles have these fitted to the vehicles as first fit - I have also been told that the software in the ECU’s have also been updated with revisions that monitor the battery voltage and engine state before either activating or deactivating the “feature” Some manufacturers have this software present from day one however each are different,” said Kambouris.
On the turbocharger side this is a little more complicated. VW for one on some of their turbocharged applications, have installed an additional electric water pump to aid the turbocharger cooling which automatically engages - battery and condition dependant - monitored by the ECU when the engine is shut off through the start/stop feature or whether the driver turns off the ignition. As a matter of interest when this water pump fails on a specific VW model, the Diagnostic error comes up as a "Pcode 0299 - boost pressure regulation pressure not reached” everyone scurries to the turbo and solenoids controlling boost etc - when in fact it is merely a water pump issue.
So, what is the issue really? It is called “hot shut down”, a thermal load which burns and cokes up residual oil in the system. The coked oil is in essence carbon build up, which at the next engine start will be forced into the bearing system which naturally acts as a grinding compound and the bearings are the victim. The issue extends beyond just the oil inside the bearing housing itself - it is the oil in the steel oil feed line which connects to the bearing housing inlet which routes approximately 20-30 mm away from the turbine housing and exhaust manifold which see temperatures of up to and beyond 650 degrees C under normal operating conditions. The amount of oil inside the oil feed line is very little and it doesn't take much to increase its temperature to above the oils flash point (The flash point is the lowest temperature to which a lubricant must be heated before its vapor, when mixed with air, will ignite but not continue to burn.) and flame/smoke point (The temperature at which the oil will stop glistening, and begin to burn/smoke)
The result is coking — carbon build up inside the oil feed line - which at next engine start up, the oil pump forces filtered oil through the feed line, forcing this coking through the turbochargers bearings causing the polishing/scoring on the bearing/shaft mating surfaces, and gradual wear between these components which will eventually relate in excessive radial and/or axial tolerance and will allow the wheels to make contact with the end housings causing catastrophic turbo failure.
Let me touch on the oil’s ignition temperature (aka Flame point) where the oil will ignite and burn. Factors that will cause/affect the flame point of oil are EGT (Exhaust Gas Temperature) which can easily range between 150 degrees C at idle and 1050 degrees C (euro 5 engines) at high engine loads. The 120-150 Deg C. flash point of motor oil (depending on the oil grade and make) easily falls within the range of exhaust gas temperatures experienced on our South African vehicles and oil combinations.
While the engine is running, the oil is flowing and will not see much effect in terms of thermal loading high enough to reach the flash point, as the circulation occurs too fast for the thermal effects to take place. However, when the oil flow stops, and the remaining oil lies stagnant inside the feed line, this is where the high temperature turbine housing and manifold will heat soak toward all the surrounding components including the oil feed line and oil inside it. Having said this, this is the normal process and operation of any turbocharger’s life. How do we prevent the oil inside the oil feed line and bearing housing from reaching its flash point? Simple allow the engine to idle to see the thermal loads settle down and lower the under-bonnet temperatures, and more importantly the EGT’s (Exhaust Gas Temperatures) before shutting off the engine. my opinion on the Start/Stop “feature” is somewhat a negative one, as a I am a vehicle owner who takes pride in my vehicles and wish to see them last me and not have to see a workshop every now and then for failures of any kind. Disable this “feature” when starting your engine every time. Always allow you engine to idle to cool the under-bonnet temperatures, before shutting off the engine after your trip, especially after a spirited drive.
If you are travelling to a destination and are able to drive the last few kms “off boost” and low engine loads, this will allow the air flow over the engine to also cool down everything, and by the time you get to your destination, you are able to climb out of the vehicle, unpack your groceries, laptop, or whatever, and then close up and then shut off the engine safely without having to worry about the temperatures. If, however you have an emergency for example - and you are driving under heavy engine loads, to your destination, leave the car to idle for at least 2 -3 minutes before shutting off the engine.
I drive a modified twin turbo V8 which is an OEM vehicle, and the HP has been increased substantially, in other words the rotating assembly runs much hotter than normal at considerably higher boost levels, and so the thermal loads are substantially higher than normal, and I always let the vehicle idle. I have done this for over 50 000 kms with not a single hiccup whatsoever. I have other clients who have bone stock vehicles which are small 1.6 Diesel turbo applications which do not see 25 000 kms before turbochargers fail and when inspection is carried out, we find that everything inside the rotating assembly is discoloured severely, indicating hot shutdowns.
Although the agents will always tell you that you do not have to let your engine idle after running, they are 100% incorrect, why take a chance in the first place. We see the after effects of the turbocharger failures daily and can confirm that if you want a reliable solution, longevity, and a trustworthy car, let her idle and cool down after your trip.
I would also suggest warming your turbo vehicle up when cold or certainly drive off boost to warm it up, until you see oil temperatures around the 50-60DegC if you have such a feature in your vehicle.
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