Just spoke to Ross, Diesel turbo's run cooler than petrol ones. The turbo on the 1.8T is watercooled and oil cooled whereas the Fabia is oil cooled only. Now who am I to question a master technician.

Also I notice o the Fabia there is only 1 heat shield to protect the brake lines on the 1.8T there are numerous ones.

Ah' date=' right...yes, the exhaust gas temperatures would be lower with the diesel being more thermally efficient.

Thought we were talking intake temperatures...

Rob.[/quote']

Intake temps would be the same before the intercooler but after the intercooler it's anyone guess, it depends on how well the intercooler works and if you have a charge cooler installed.

What good does that do?

I think you need to read the TDI FAQ mate... the car will not warm up AT ALL if its just idling' date=' so all you are doing is wasting diesel.[/quote']

It would start to push oil back into the bearing surrounding the turbo thought ?

Intake temps would be the same before the intercooler but after the intercooler it's anyone guess, it depends on how well the intercooler works and if you have a charge cooler installed.

Well, like for like, they'd be the same...

And surely unless the car had been sat for a long time, there would be oil around the turbo bearings anyway? Everywhere I've read (manufacturers handbooks and the like) all say that idling at startup is a bad thing. They don't say why, but I suspect it's because the engine takes longer to warm up yet is being worn much the same as if the car was moving. Or, they're lying, and they just want everyone's engines to fail so they can clean up on repairs/new cars...

Rob.

Always let car tick over in the morning until the auto-choke drops the revs to mormal(approx 1 min) and whenever i stop i take it easy for the last couple of miles before i get home and let it tick over for generally 2mins.

Well' date=' like for like, they'd be the same...

[b']And surely unless the car had been sat for a long time, there would be oil around the turbo bearings anyway?[/b] Everywhere I've read (manufacturers handbooks and the like) all say that idling at startup is a bad thing. They don't say why, but I suspect it's because the engine takes longer to warm up yet is being worn much the same as if the car was moving. Or, they're lying, and they just want everyone's engines to fail so they can clean up on repairs/new cars...

Rob.

The viscosity of oil when hot reduces, so the likehood of the oil draining out when the engine has been swtich off is higher surely ? So when you start the engine the oil will be in the lowest part of the engine, there will be traces of oil on the bearings possibly but not enough to protect it fully until the oil pressure has built up ?

What good does that do?

I think you need to read the TDI FAQ mate... the car will not warm up AT ALL if its just idling' date=' so all you are doing is wasting diesel.[/quote']

erm....what david said! :eggface:

The viscosity of oil when hot reduces, so the likehood of the oil draining out when the engine has been swtich off is higher surely ? So when you start the engine the oil will be in the lowest part of the engine, there will be traces of oil on the bearings possibly but not enough to protect it fully until the oil pressure has built up ?

Guess a lot would depend on the type/age of the oil in terms of run back.

Still, it's not going to take that long for the oil to be pumped back up to the turbo...certainly not a minute or two...

Rob.

Always let car tick over in the morning until the auto-choke drops the revs to mormal(approx 1 min) and whenever i stop i take it easy for the last couple of miles before i get home and let it tick over for generally 2mins.

It's not a great idea to let the car warm up at idle: it can result in worn bores. Most handbooks advise against this: ideally, you should drive off as soon as you start the engine, but treat it gently until it's thoroughly warmed up.

It's not a great idea to let the car warm up at idle: it can result in worn bores. Most handbooks advise against this: ideally, you should drive off as soon as you start the engine, but treat it gently until it's thoroughly warmed up.

Worn bores or glazed bores ?

Worn bores are going to happen when you drive so no difference there. Personally I let the oil pressure build up first maybe not for 1-2 minutes but for about 30 seconds or so.

I have seen the effects on an engine where the person had driven off briskly from cold.

It's not a great idea to let the car warm up at idle: it can result in worn bores. Most handbooks advise against this: ideally, you should drive off as soon as you start the engine, but treat it gently until it's thoroughly warmed up.

Can you just expand on that as I'm a bit :confused: As I understand it, the oil in the engine sits in the sump and when you start the engine, the oil pump sends it round. So oil should reach all parts of the system pretty quickly (anyone know how long?!)? If there is relatively little oil in the engine, as the engine is "cold", isn't it better to let it tick over at 900 rpm rather than drive it at 3k rpm, or are you saying that driving is better at heating the oil which means it's distributed quicker around the engine so you should do that? My understanding is probably wrong though so please be gentle

Chris

Sooner it dies, sooner I can put a better one on without having to justify it to SWMBO, it's broken love

But really I pootle home from m-way, and leave to idle for 4-5 mins if pulling in from A/B blast.

Worn bores or glazed bores ?

Worn bores are going to happen when you drive so no difference there. Personally I let the oil pressure build up first maybe not for 1-2 minutes but for about 30 seconds or so.

I have seen the effects on an engine where the person had driven off briskly from cold.

wonder if my 172 has blown up yet as that was driven hard from cold every day usually to red line by the end of the street lol

fabia i dont let warm up either i dont care tbh if it fails it fails i doubt it will be my car when it does

Nick - dry to an extent. Its not no oil pumping around' date=' but substantially less than if you were to let it spin down naturally.

Rob sounds about right, i'm sure its the air friction causing more heat rather than the thermodynamics of the engine.[/quote']

Hmmm - not so sure about this. What I think we are talking about is a cooling effect, rather than lubrication. Oil has two purposes in an engine, lubrication and cooling. Letting the turbo spin down gently will keep the oil circulating and thus cool it down. I guess if just turned off when hot, the oil can vapourise and leave the bearings dry. Then if restarted immediately there might be damage to the bearings.

Most of the heat in the turbo comes from the fact that it's driven by exhaust gas straight out of the engine - friction should be a negligible component of that, although adiabatic compression probably raises the temperature a few degrees.

Nick I read something about the oil vapourising, it leave a residue on the bearing which can build up and cause issues. It creates a tar like substance which I presume would effect oil flow through the bearings causing premature wear.

Nick I read something about the oil vapourising, it leave a residue on the bearing which can build up and cause issues. It creates a tar like substance which I presume would effect oil flow through the bearings causing premature wear.

Not heard of vapourising, but I've heard of coking which will clog the bearings...though this doesn't happen with modern synthetics...

Nick - do modern turbos really need to be cooled down? Thought this was also a historical hangover from older bearings which used to seize if subject to too much heatsoak?

Rob.

So why all this talk of protecting turbos at all then? The oil vapourising / coking was the only explanation I could think of - although I suppose differential expansion might come into it ...

Not heard of vapourising' date=' but I've heard of coking which will clog the bearings...though this doesn't happen with modern synthetics...

Rob.[/quote']

Remember Rob the oil in the Fabia is Semi syn from the factory.

Remember Rob the oil in the Fabia is Semi syn from the factory.

It is possible for semi-synthetics to comprise anti-coking agents - depends on the oil...

Rob.

So why all this talk of protecting turbos at all then?

No idea...

Rob.

It is possible for semi-synthetics to comprise anti-coking agents - depends on the oil...

Rob.

I thought the idea of adding synthetics was stop sheering of the molecules.

I thought the idea of adding synthetics was stop sheering of the molecules.

Dunno...I'm not an oil engineer, or anything even close to it...

Rob.

You need to protect the engine by idling it before switch off if the engine has been under high loads. This is due to heat soak (the rise in temperature that occurs once the system becomes stationary).

As for bore wear when idling a cold engine: I'm not quite sure why this is necessary, but I've been told to include it in handbooks in the past by engineers. I think it's to do with the fit of the rings in the bore when the engine is cold, and the lack of oil in the bores: you need to get the engine warmed up fairly quickly, so that the pistons become a good fit (stress causes the pistons to change shape as they warm up, which is allowed for when they are designed).

It's mentioned in the Fabia handbook, as well.

The Octavia manual states you should move off as soon as you start the engine.

As for cooling down, taking it easy for the last few miles or running the engine for a couple of minutes is hardly an inconvenience, so i do it as much as possible.

You need to protect the engine by idling it before switch off if the engine has been under high loads. This is due to heat soak (the rise in temperature that occurs once the system becomes stationary).

But TDIs don't get hotter when stationary... You can't just sit on the driveway in the morning and wait for the engine to warm up, 'cos it won't. It needs to be driven.