Simple Mechanical/Engine Questions

Hi,

I'm new to the forums but have owned a tdi (2 jettas and now a passat) since I have been able to drive at the age of 17 (I'm 40 now!), so I love the car. I searched the forums for a while and can't quite come up with answers to the following few questions. There are a lot of mechanics/service/experienced people here whom definitely know their stuff - I can safely say they have lost more knowledge about tdis/mechanics than I'll ever know, so I thank you for the responses in advance.

1. This doesn't relate to TDIs per se, as it applies to any engine. How harmful is it to drop an automatic out of gear into neutral and just let it coast and then throw it back in. For example there is a long downhill road by my house that I can easily coast down for over a mile, then when I have to stop at the bottom I would throw it back in gear so I can make the turn after the stop. Is this a big no-no or is it ok/not engine harming? I harken this to leaving the lights on in a room because turning the bulb off for a few minutes is bad wear and tear on it (allegedly).

2. Anti-Gelling additive. Whats the temperature that its a "good" idea to add it in? I know each manufacturer has their own specs but what does "real world" knowledge say?

3. Does using the cruise control get better or worse MPGS? I've been reading how much better many people MPGs many people are getting and I'm going to try and drive a bit slower (I do 80-90 mphs every day, 100 miles a day). I currently get 39.5 mpgs at that speed and I in the process now of actually driving the 65 mphs speed limit for two consecutive tank fulls of fuel to see how much it improves....its hard, so very hard to not hop in the left lane.....

Thanks!
Ed

ps I'm attorney so while I'm only licensed in NY and CT, I'm happy to give "advice" on topics if I know what I'm talking about!

I'm sure I'll think of more sooner rather than later.

1 I doubt there is any harm in shifting to N for a downhill coast. But there is also no significant benefit to doing so. Especially if at the bottom of the hill you need to slowdown anyhow. In that case the engine windmilling is burning zero fuel and saving your brakes as well.

2. Your fuel from the station should be ok with no anti gel additive. Also, once running, the vw fuel system adds heat to the fuel so it makes it less an issue.

3. Cruise or foot control will get very similar mpg. A smart foot is better than cruise on ascending/descending so if in hilly runs, ditch the cruise and use the foot.

1. - Coasting in neutral is really a bone headed idea. You will save vary little fuel and loose the engine braking coasting in gear provides. In most places it is illegal because on a very long hill you could cause your brakes to over heat and fade resulting in you rear ending slower traffic.

2. - The only problem you might have is if you fuel were the fuel isn't winterized yet and drive to were the temps are substantially lower.

3. - Cruise is kind of a mixed bag. It can't anticipate times when you might let the speed increase to help you over the next hill.

Probably the best mileage would be achieved by driving at less than 50 MPH with no starts or stops.

Ol'Rattler said:

1. - Coasting in neutral is really a bone headed idea. You will save vary little fuel and loose the engine braking coasting in gear provides. In most places it is illegal because on a very long hill you could cause your brakes to over heat and fade resulting in you rear ending slower traffic.

Click to expand...

Not boneheaded at all. I see his reasoning, and it's an automatic, not a standard, so say goodbye to the compression braking.

He also lives in CT, where the highest hill is tiny compared to WA, so no need to worry about brake fade.

I think the 02E DSG in the 2012 Passat TDI already has a freewheeling feature on decel at higher speeds with your foot off the brake. I do not have my B7 study guide here so I will have to check for sure. But I know it is NOT the exact same 02E as found in the Golf/Jetta/Beetle/A3.

oilhammer said:

I think the 02E DSG in the 2012 Passat TDI already has a freewheeling feature on decel at higher speeds with your foot off the brake. I do not have my B7 study guide here so I will have to check for sure. But I know it is NOT the exact same 02E as found in the Golf/Jetta/Beetle/A3.

Click to expand...

You are once again correct. The DSG will freewheel on downhill until the brakes are applied where it will engage the engine to help reduce speed.

I can't quote this but i had read somewhere that the DSG needs to be engaged in drive to properly lubricate the clutch discs. It may even be in the manual.

Abacus said:

Not boneheaded at all. I see his reasoning, and it's an automatic, not a standard, so say goodbye to the compression braking.

He also lives in CT, where the highest hill is tiny compared to WA, so no need to worry about brake fade.

Click to expand...

It is indeed boneheaded.

All automatics today including the DSG use engine speed to circulate the fluid.

My manual specifically says NOT to move the car in Neutral (under towing section) because of this lack of cooling issue!!!

oilhammer said:

I think the 02E DSG in the 2012 Passat TDI already has a freewheeling feature on decel at higher speeds with your foot off the brake. I do not have my B7 study guide here so I will have to check for sure. But I know it is NOT the exact same 02E as found in the Golf/Jetta/Beetle/A3.

Click to expand...

Correct. I can speak to this irritating feature. I like to have engine breaking instead.

Abacus said:

it's an automatic, not a standard, so say goodbye to the compression braking.

Click to expand...

It's an automated manual, and it does engine brake.

Elfnmagik said:

It's an automated manual, and it does engine brake.

Click to expand...

2009 Jetta DSG, yes, engine braking.
2012 Passat DSG, no, see above.

I'm with TomB on this one...I'd prefer the engine braking (but NOT "engine breaking")

Correct on the DSG in the Passat vs. prior versions of the DSG. I felt as though the statement I quoted was a generalization of differences between the slush box autos vs. manuals.

TomB said:

Correct. I can speak to this irritating feature. I like to have engine breaking instead.

Click to expand...

I'd rather have a proper manual in the first place.

TomB said:

Correct. I can speak to this irritating feature. I like to have engine breaking instead.

Click to expand...

Doesn't the transmission re-engage and disable free wheeling if you touch the brakes?

One more. The family mechanic, who works on Ferrari, Lamborghini, etc (I loved driving my old TDI into his shop with its 350k miles on it and its beat up body and leaving it there) swears that, despite no mention of it in the owner's manual, that starting the car up for a few minutes before actually driving it helps save alot of engine wear and tear because its gets the oils flowing etc. This is similar to the thread of warming up the engine before going full throttle, but slightly different. Any truth to this at all?

Actually, the manual DOES mention this: it says NOT to do it.

dweisel said:

Doesn't the transmission re-engage and disable free wheeling if you touch the brakes?

Click to expand...

Kind of sort of.

I just don't see the same braking as with the 2005's.

It does NOT downshift or anything so I still have to push over to tiptronic and DOUBLE down shift or put in Sports mode. In Sports mode it will downshift for better control.

oilhammer said:

I'd rather have a proper manual in the first place.

Click to expand...

Where is the like button?/