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MG MGF Technical - A day out on B-roads and a infrared thermometer...


Hi all,
I have done some testing as to what temperatures to expect in and around the engine compartement. The driving was performed with closed engine cover (the one with umpteen screws ) but easily accessable in a few seconds so not to disturb accurate measurements.
The instrument was a "Linear Labs C-600E handheld infrared thermometer.All "extras" as normally on my car was returned to normal so no extra airintake scoop etc. was used. And here is whatīs found ;

1. Air entering from underneath and from side-intakes seems to be more than enough when traveling at 40 km/h or above. This is evident as engine lid simply lifts fully at the rear end if not secured by at least one bolt ! With the ability to further escape thru the vents is another story. IMO these vents are far to small. When the boot was opend slightly the lid fell down and stayed down at any (reasonably) speed.

2. Measured temps was after fairly brisk driving.
Inlet water before thermostat : around 70-75 deg. C.
Just after thermostat : around 85 deg. C.
Alu part at the head on intake side: around 90-95 deg.C
Same but at exthaust side : 93-97 deg.C .EXCEPT AT THE RIGHT HAND CORNER ABOVE ALTERNATOR ! Here the temp was 100 to 115 deg. C ! This measured just in the vicinity of the heat shield. After the engine had cooled down enough I removed the heatshield and renewed measurements gave much lower temp ! Now it was the same as on the left corner, i.e. 93-97 deg.C.
The emissivity factor for the instrument was altered but no adverse effect from the shiny heatshield could be measured. So it seems that the heatshield that shall protect the alternator actually worsens the temp at that corner of the head. Funny was that removing the shield had little effect on alternator temp. That was a steady 80-87 deg.C even when engine was running and car was parked. All 4 exthaust outlets had the same variation in temp ,going from around 280 deg.C at idle to a hefty 420 at full throttle.
So the question is ; Is that heatshield doing more harm than good ?? Any comments welcome.

Regards , Carl.
Carl

I promise, Carl didn't ask me ...
.. but here is a picture ;)

Rear look to the just diassembled subframe.
The alternator on the left and the heat shield between alternator and manifold, is it ?
http://www.mgf-net.de/engine/rear_full_cp_3895.jpg
http://www.mgf-net.de/engine/ are two more from above of the area (shield indicated with purple arrow)

Carl, I wonder about that result, cause I meaned the side fan would cool the alternator area ?

It should IMO if the hot car gets parked and the engine compartment temperature sensor forces the fan on for 10 Minutes.
This case should get measured also, with and without shield (IMO)
Dieter Koennecke

I have seen much higher temps on the exhaust side as well when I was doing some testing last Autumn. I haven't restrarted from where I left off, but interestingly the temps measured in the F engine bay were mostly lower than those in our standard Rover 218iS - hence the need to continue the testing.

Rog
Roger Parker

So the heat shield is trapping heat in the exact same corner as the majority of reported HGFs occur...

It certainly seems much more than pure coincidence doesn't it?

If heat shielding is required for the alternator, then perhaps exhaust insulating tape around the manifold could be used in preference?
Rob Bell

I wouldn't rush into dispensing with the heat shield

I have seen a Cup Car engine with heat shield which after racing had melted its plastic alternator end cover. I was told it was a fairly common ocurrence.

jt
John Thomas

Hi,

This is good stuff Carl. I'm always interested when someone throws yet another spanner into the works. I assume that to get the temperature readings you had to stop the car(!), whip open the relevant part of the bodywork, and take the readings as quickly as possible? I also assume that the readings are the surface temperatures of the engine components.

I'm quite surprised that the inlet (i.e. cool side) temps are so similar to the exhaust side, I would have expected quite a difference, what with air and evaporating petrol in one side and raging flames out the other. I wonder what you're seeing, Carl, is a boundary layer temperature? (Well, of course, to an extent it's bound to be, what with combustion temperatures being up in the 2000 to 3000 deg C range.)

I find it difficult to explain to myself how the heatshield could cause such a rise in the engine temperature at that point. Heat from the engine can only dissipated by radiation or convection into the passing airflow. The heatshield hardly looks close enough or large enough to stop much radiation, and it's mainly end-on to the engine. Besides, the two shields seem to concentrate heat onto the centre part of the engine, and not reflect it back to the dodgy front corner. Air-flow does look pretty restricted, with the alternator adding to the congestion in that area, but I would be surprised if restricted air-flow could cause around 15 deg C difference here. It's a large difference, and the air-flow can't be great with or without the shield. The engine bay fan, which is bound to be mentioned, blows across the engine quite a way forward, amd doesn't appear to cool the alternator area much.

Well, what doesn't speak doesn't lie, so if these temp readings (and shield on/off differences) can be repeated then I'll willingly believe them. I'm just trying to rationalise the readings! I'll try to set up my air temp thermometer to take some comparisons. Perhaps we could have a modified heat shield that doesn't shroud so much? Or maybe point the K&N pipes to the top of the alternator?

On another subject, Dieter's pictures show the short bypass hose quite clearly. This is as fat as the heater returm hose (into which it discharges), so maybe there's not much to be gained by having the heater on all the time (as I do), apart from a sense of well-being, that is. Dieter, did the engine in the engine/subframe pictures have air-con, and Carl, does yours?

Regards, Kes.
Kes

>did the engine in the engine/subframe pictures have air-con,

Yes, it had. the compressor is already dismantled from below the alternator, but the three fixture threads can be identified easy as shining points.
http://www.mgf-net.de/engine/rear_full_cp_3895.jpg

Guess Carl hasn't got an aircon. What should it be good for in Sweden :)
Dieter Koennecke


Hi all,
just in from a long journey without IT-facilities so will answer in a short way and respond more later on... I have been unclear about the point of increased heat; it was on the inside of the heatshield NOT on the alternator side ! I too got puzzeld by Dieters pict. as his alternator fixings doesnīt correspond to mine (no air-con.)

Will be back in the weekend with more....

Regards , Carl.
Carl

Just drive the damn car guys !

But anyway - why measure air temp outside of the alternator? This proves nothing about the alternator internals, reflectivity, absorption or conductivity. Just how much hot air is moving around - I'd have thought a probe was required at the very least.

That doesn't even begin to allow for air velocity on the move. Oh no I'm turning into an anorak too....
James


James , itīs an infrared measuring eq, = measures the actual temp on the surface of a part. In this case at a distance of about 20 cm with a measured area about 20 times 20 mm ! Wich means contact-less accurate temp.-measures even at "hard to get at" places.

regards , Carl.
Carl

This thread was discussed between 05/05/2001 and 11/05/2001

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