Cold Start: How to Safely Merge onto Highway

Now that I've had a new engine installed in my Polo, I want to drive it even more gently than I already do. However, I encounter the following situation every day, which is extremely hard on the materials and unavoidable:
- The car is parked outside every day, and after a cold start, I have to merge onto a two-lane highway with heavy traffic within a maximum of 200 meters. To make matters worse, it's also an uphill climb. Now I have the following question: what do you think is less harmful to the engine? 1) Keeping the RPM as low as possible until 2500 RPM, or 2) Staying below 2000 RPM and driving with a lot of load? It's a 1.4 TDI engine.

Joohn wrote:

What do you think is less harmful to the engine: 1) keeping it at as low a load as possible up to 2500 RPM, or 2) staying below 2000 RPM and using a lot of load? It's a 1.4 TDI.

I would go with option 2: Cold oil with high viscosity is very stable, but not yet ideal for lubricating rapidly moving parts.

Depending on how sympathetic you are to the engine, especially during winter, I would also consider a short warm-up period (around 5 minutes) at low speed before getting onto the highway.

As Ulf already mentioned;
When the engine oil is cold, it's better to keep the engine at lower RPMs than to rev it up excessively under low load.

And since it's not working to warm up the engine gently, make sure to pay attention to the oil quality and maybe change it sooner.

Best regards, Georg.

Okay, thank you very much, I will keep that in mind!

Georg-TDI wrote:

Always pay attention to the quality of the oil

.
Hi Georg,

Can you perhaps give me some specific tips on this (besides using oil that meets the VW specifications required by the engine)?

In
http://www.ibiza-forum.de/thread.php?threadid=16730
(take a lot of time to read through )
According to a (presumably) knowledgeable person in the oil industry, it essentially doesn't matter which oil you choose as long as it has the same VW approval, and that expensive oils only benefit the manufacturers/sellers.

To make matters worse, it's also going uphill.

Why, there's nothing better than a mountain to help you warm up! The engine has to work hard and heats up quickly.

Driving downhill on the highway would be a nightmare for a cold engine! It's extremely cold, the engine speed is constantly high, and very little fuel is injected.

It's important to upshift early (in 1st gear at 1300 RPM, in 2nd and 3rd gears at 1600 RPM, in 4th gear at 2000 RPM, and initially only use 5th gear up to 2000 RPM, which should be sufficient for speeds of 80-90 km/h).

Best regards,

SeatArosa1.7SDI wrote:

Why, nothing could be better than a mountain for warming up your engine! The motor has to work hard and will quickly get warm.

Well, but during the rapid heating process, the temperature will initially distribute more "patchily" within the block/heat sink, which increases the thermal stresses compared to a slower warming .

The question is whether this will ultimately be more harmful than a slower warming process with "longer cold" oil, etc., but with lower temperature stresses...

'The important thing is: shift up early (shift to 1st gear at 1300 RPM, shift to 2nd and 3rd gears at 1600 RPM, shift to 4th gear at 2000 RPM, initially only use 5th gear up to 2000 RPM, which should be sufficient for speeds of 80-90 km/h).'

I usually do it that way too, as much as traffic allows! Since it vibrates quite a bit in the 4th gear, mainly at 1600 RPM, I occasionally drove in 3rd gear up to around 2400 RPM. But I will try to keep it below 2000-2200 RPM in the future.

Well, but during rapid heating, the temperature will initially distribute more like 'spots' within the block/heat sink, which increases the thermal stresses compared to a slower warming process .

As long as there are no stress cracks in the block, I think thermal stresses are irrelevant. I've always given my engine a good amount of throttle (full pedal) when it's cold and running below 2000 RPM. It has survived perfectly well for 100,000 km. Although, being a naturally aspirated engine, it is generally more robust due to the lower power density.

And one more thing: As long as the temperature gauge reads below 70°C, I will avoid using the fan, close all the air vents, and wipe the fogged-up window with a cloth. With this limited amount of heat, the engine should be allowed to warm up properly on its own.

The vibrations caused by resonances in the engine mount at low RPMs are a problem. Mine vibrates like crazy at 1300 RPM and under heavy load. That's why I try to stay away from that RPM range as much as possible.

Best regards,

Hi,

Quote:

I've always given my car a good amount of throttle (full pedal press) when it's cold, even at engine speeds below 2000 RPM.

For an SDI engine, this might be acceptable (although I'm not entirely sure about that), but I would strongly advise against doing it for a TDI engine. A VTG turbocharger already reaches its maximum boost pressure around 1500 rpm at full throttle, which leads to corresponding engine speeds (okay, those are higher at 4000 rpm because the volumetric flow is greater, but it's likely to be significant even at that lower speed) and a corresponding load on the crankshaft.

Currently, my strategy is to keep the boost pressure below 0.5 bar when the engine is cold, and only give it full throttle and rev above 2000 RPM once the oil temperature reaches 70...75 degrees Celsius.

If I immediately get on the city highway after starting (which is about 500 meters from here), it's not that easy because to keep the pressure below 0.5 bar, you can't really accelerate hard – the full boost pressure often kicks in long before the wheels touch the ground.

Best regards,

January.

Hello,

I've always given my car, when cold, a good 'kick' (full throttle) below 2000 RPM.

When my VTG was constantly sticking after a cold start and unable to build boost, I did something similar, but only up to 2000 rpm. Pure SDI feeling . Since on a TDI, the soot limiter kicks in very early when there's no turbo boost, there shouldn't be any problems because the engine then accelerates very sluggishly. You can press the gas pedal as much as you want, but almost nothing happens (it's not fun when a cyclist pulls away from you at the traffic light ). I think it will probably be similar with an SDI.


If I immediately drive onto the city highway after starting (which is about 500 meters from here), it's not that easy, because to stay below 0.5 bar of boost, you really can't accelerate too much - the full turbo pressure often kicks in long before the wheels leave the ground.

I can confirm this as well, since I also 'warm up' my AFN after the LDA. When slowly increasing the engine speed, around 1600 rpm, the LD pressure quickly reaches 0.7 bar without much throttle input. A slight twitch of the right foot is enough to make the LD pressure jump to 1 bar.
IMO, a pressure of 0.7 bar might be relatively uncritical because while the LD (likely referring to Lambda Direct or similar) is present, the amount injected is limited by the driver. Therefore, the peak pressures in the engine should also be lower since the maximum fuel quantity (driver request < soot or torque limitation) is not being requested. Or am I mistaken ? I'm not a graduate .

Hi,

I studied something completely different... it has nothing to do with cars.

I consider the peak boost pressures at 0.7 bar of boost to be not critical, given that even under light load, more boost is likely to be applied. However, also consider the turbocharger itself. It will receive relatively cold oil and needs to spin significantly faster than it would at 0.5 bar.

Someone posted these charger identification fields at some point; the relevant charger speeds should be readable from them.

That's certainly tens of thousands of revolutions per minute.

Best regards,

January.

Hi,

I consider the peak pressures at 0.7 bar boost pressure to be not critical, considering that even with low load, there is already a lot of knock occurring. However, think about the turbocharger. It will also receive relatively cold oil, but it has to spin much faster than at 0.5 bar.

I had also considered that before, but then dismissed it as insignificant. 0.7 bar is just my personal limit because with 0.5 bar, there's less thrust (which, in my opinion, is also too moderate for the warm-up phase).
But you're right about that, especially since my turbo is now 'tuned' (>> shaft length) and that means the spool-up of the charger is accelerated much faster (higher angle of attack of the variable turbine geometry - VTG) than with a 'normal' factory setting. Therefore, applying the throttle during cold start is even more critical now to avoid unintentionally building up 1 bar of boost pressure .

'It's important to: shift up early (in 1st gear at 1300 RPM, in 2nd and 3rd gear at 1600 RPM, in 4th gear at 2000 RPM, initially only drive the 5th gear up to 2000 RPM, which should be enough for 80-90 km/h)'


Every diesel driver who doesn't do that would constantly have to get a new engine and turbocharger... But I don't feel that kind of demand in the workshop. An engine that is driven normally will also withstand it.

Best regards,

Sure, here is the translation of the text from German to English:

"Hi,"

Many engines can handle full throttle immediately after a cold start and still function. Something won't necessarily break down right away, and I don't think you'll notice the effects quickly, but eventually it will show consequences... perhaps long after 100,000 kilometers.

Best regards,

January.

Well, but can it handle a boost pressure of 0.5 bar? A turbocharger gets hot from the exhaust gases anyway.

Best regards, WarLord.