Piston Slap: That Slow TSI Coolant Burn?


VW EA888 Engine exploded view, Image: VW

Jonathan writes:


Our 2016 Passat (turbocharged 1.8-liter four-cylinder) appears to be losing coolant at the rate of a quart per year. We are driving the car only 5,500 miles per year in Chicago, so the coolant system isn’t under a whole lot of loan most of the year. I don’t have any spots on the garage floor under the engine, and the dealership checked for leaks and couldn’t find any.

The dealership did say that turbo engines are expected to eat some oil and coolant, and that there is nothing to worry about. Is that really a thing? I am very skeptical, but I know very little about maintaining engines with a turbo.

What say you?

Sajeev answers:

As mentioned previously, many a modern mill is cool with oil consumption. Perhaps tolerances on your turbo’s internal water cooling and oil cooling/lubrication-infused bearings are such that, in theory, the VW EA888 motor and its BorgWarner K03 turbo could burn coolant even at such a young age. But there’s another reason why…

The EA888’s exhaust manifold (that feeds the turbo) is internal to the engine!  More to the point, the engine’s coolant passages snake around the exhaust manifold runners, then spit coolant in (and suck it out) of the turbocharger. Engineering Explained covers this cooling system (starting at 4:20), so we can extrapolate if/how this causes coolant loss.

Can this integrated exhaust manifolding mean coolant is under more heat/pressure to perform? And perhaps does it creep past seals and burn up at those stupidly fast and hot turbocharger bearings?

But I wouldn’t worry about this slow TSI Coolant Burn, because there ain’t much you can do about it. Do whatever maintenance the owner’s manual says (or not). If your Passat consumes a quart of coolant monthly, if the warranty expires, I am sure a rebuilt turbo (built in your specific housing) won’t be too painful on the wallet, since there are standardized guts within that case. And mercifully, that TSI designed case isn’t that unique in VW Land.

What say you, Best and Brightest?

[Image: Volkswagen]

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.