Stuarts Turbo cooldown note

I have installed a thermocouple (type-N) on my exhaust manifold, just above the turbo-outtake, and jamed between the rust (I just love cast iron...), and the heat shield, I run this into an in-cabin digital volt meter, and therefore can monitor exhaust manifold temperature (well, atleast a guide to..)

BTW: I am talking about a 3l MA70 turbo automatic on 96 octane unleaded.

So far I have found the following;

1 - thermocouple scaling: at room temp: 0mV at 100'C (boiling water), 2.1 mV

note: thermocouples are *not* linear, I am working on a mV to temperature conversion, but do not have a good one for type-N yet..

2 - Max temp found so far under bonnet - exhaust piece on turbo ater drive home (20 minutes, being nice..) - 13.5 mV (this is not in the place I now measure..)

anyway: now for readings of the 'standardised' location..

during warmup on cold morning: 2.0mV in 4 minutes idle, engine temp increases 1 'notch' (digital dash - around 5th notch for normal temp.) at this time, increase seems quite linear, first 0.8 mV more quickly.

easy motorway driving, 100 Km/H, around 4.1mV (on way to work, 20 minute+ 5 minute city drive)

hard(ish) overtaking, up to around 130-140Km/H, around 4.7mV, but it takes a good 10-20 seconds to rise, drops even faster when I back off.

Sitting at lights in town: slow drop towards around 3.8 mV

5 minute 'thrash' - OD off on auto, hard suspension, well known emptyish curvy roads at around 140-160 Km/H, 5.6mV peak.

I have yet to really push it, I suspect I can easily excede 6.5mV..

anyway, the important bit: cooldown:

ariving at work: 2 minutes at idle gives cooldown from 4.1mV - 3.5mV. Will keep dropping to around 2.4mV after 10-20 minutes.

I 'feel' that, in the current location, around 3.5mV is a good 'turnoff' temp, so I will start looking at the times required to get to 3.5mV and 3 mV from my 'finishing' temps.

also: it seems hat short 'overtaking' type hard usuage does very little to the exhause manifold temp, perhaps 0.5mV increase, it is the long periods at high RPM/boost (ie: OD off thrashing) that makes the heat.

temp takes around 10-15 minutes to settle from cold with carefullish driving. any longer trips add no noticable increase in temp.

I will start adding to this, then we will have an answer (or at least a few more hard facts) about how we should cool down.

> > No, there is no source of heat that high...
> >
> > I know what you are taking about, the way that when you turn on the
> > engine the 'temperature' guage is higher (say, after 5 minutes) than
> > normal, right???.
> >
> > Remember, this is the *water* temperature, normal is just a bit under
> > 90'C I believe, but the exhaust manifold (what I am reading..) can be
> > around 200 'C after cooldown (and over 500'C when working..)
> > , this heat 'soakes' into the water (and
> > the oil, turbo, etc..) increasing it's temperature. The hot water
> > goes to the top, and your water temp sensor is also at the top, so it
> > reads the highest temp. Don't worry about this, it is perfectly
> > normal. (unless I am taking about the wrong thing here...)
>
> Yes, I realize that.  However, since the turbo is water-cooled and
> oil-cooled it seems reasonable to expect that the turbo temperature
> might go up immediately after shutdown as heat from the manifold soaks
> into the turbo casing.  Are you reading turbo temp or manifold temp?
> >From your previous post it sounded like maybe you are reading the temp
> at the manifold/turbo interface.  Is that right?

heat soak into the turbo is *the* problem.. and I am tryint to guage this, but water will *always* cool the turbo as it is soo much hotter than the water ever gets, and water is quite thermally conductive..

I'm not confused about what you are looking at. my current theory looks like this.

water=coldest.

compressor side of turbo = next coolest

exhaust manifold = next hottest

exhaust side of turbo = real hot (where the exhaust pipe exits the turbo..)

to heat will soak all over the place. I have yet to investigate the exhaust manifold/turbo well for hot-spots, due to the heat-shields (and lack of time..), but I believe this is approx. accurate.