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Joined: Nov 16 2016
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Wonder if there are any real world benefits from keeping the throttle body heating on a P38?
Bit ironic that the subject should fall under 'oily bits' section lol - you wouldn't want oil in the water.

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Joined: Dec 30 2015
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Yes there is if you don't want it icing in cold, damp weather. The air intake is under the inner wing so the air being drawn in is at ambient temperature so will ice on the throttle butterfly in the right conditions. Of course it falls under oily bits, as it says, if it leaks, it's in here and the hose for the throttle body heater is known for leaking, which is why it gets replaced with silicone hose.

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Joined: Mar 22 2016
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Typical, I’m late coming online, I have a top hose with the plastic tee, brand new, I butchered one of the hoses from it, lol..

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Joined: Dec 30 2015
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It's OK Chris. For the price I may as well get the whole thing replaced. I'll keep the old hoses in the useful bits bin. I might swap the jubilee clips on the new one for the proper clips on the old one, assuming they're still good.

I've got my temper back now, I was getting a bit p'd off that I'd turned a working car into a broken one and burnt myself in the process. Now my arm has calmed down I think I'll just chill until the weekend and swap it all over.

I'm still confused as to why the aircon compressor wouldn't lift off - have I missed any bolts? I've got all four obvious ones.

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Joined: Nov 16 2016
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Gilbertd wrote:

Yes there is if you don't want it icing in cold, damp weather. The air intake is under the inner wing so the air being drawn in is at ambient temperature so will ice on the throttle butterfly in the right conditions. Of course it falls under oily bits, as it says, if it leaks, it's in here and the hose for the throttle body heater is known for leaking, which is why it gets replaced with silicone hose.

I know the theory but wondered if they really do suffer icing in the wrong UK conditions if unheated, plenty injected vehicle models don't have tb heating (I don't remember if L322 BMW V8 tb's are heated), the iav isn't heated..
Second line was meant in jest..

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Joined: Dec 30 2015
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Mine was fine last winter, and I did drive it during icy conditions. I suspect it's only a factor in places like Canada or the NW states of the USA. Maybe it's a hangover from carburetor days.
I guess the ultimate test would be to drive it at a constant throttle opening through freezing fog, not that I'd dare :)

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Joined: Jan 05 2016
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I think the throttle body heater is only really useful in seriously cold climates while the engine is still cold. The coolant will warm it up quicker, but once the massive block of metal is up to temp below it, I can't see it adding anything.

Either way mine is gone all together.

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Joined: Mar 22 2016
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I can’t see any reason why with the 4 bolts undone it didn’t lift, there it a locating dowel which it must be stuck on, get a lever under the AC pump and give it a wiggle.

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Joined: Dec 30 2015
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Yeah, I got a decent sized spanner under it and braced it off the alternator. I gave up when the spanner started bending! From what you say it sounds like the side loading would have jammed it on the dowel. I'll find the dowel and plus-gas it before I try again.
Thanks Chris!

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Icing happens when the temperature is above freezing, anything up to 5 degrees, but when there is a lot of moisture in the air. The airflow through the throttle body is accelerated so cools and forms condensation on the throttle butterfly which turns to ice with the airflow. Yes, it is worse on an engine on carbs because the venturi in the carb body accelerates the air by a greater amount so gives a greater cooling affect. That's why older stuff had a swivelling nozzle on the air intake with summer and winter settings so in winter it drew air in from around the exhaust manifold. You certainly know about it when it happens as the air intake gets partially plugged with ice so the mixture goes ridiculously rich and the throttle won't close due to the ice build up. Idling a cold engine at 4,000 rpm isn't to be recommended......

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Joined: Mar 22 2016
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Morat wrote:

Yeah, I got a decent sized spanner under it and braced it off the alternator. I gave up when the spanner started bending! From what you say it sounds like the side loading would have jammed it on the dowel. I'll find the dowel and plus-gas it before I try again.
Thanks Chris!

I’ll pop mine off later and send you some pics, gotta have a play as my ABS pressure sensor has died,, woo hoo when you hit the brakes and pedal keeps sinking, lol

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Joined: Nov 16 2016
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Agreed icing is much more likely on a carb engine because the throttle plate has a mist of petrol flowing over it, some evaporates as it shifts from the atmospheric pressure to the low pressure side (with velocity increasing etc), as the petrol evaporates it has a high cooling effect that is in addition to the cooling effect of air pressure and velocity changes. An AC system filled with just pressurised air would still work but only very slightly not to the extent you'd notice but filled with a substance that changes phase from liquid to gas it works a lot better.

Besides the dowel, does the AC compressor have any collared bolt holes... so as you tighten the bolt the collar in the bolt hole pulls into a recess in the compressor (same as often seen on alternator mountings)? Some vehicle models do.

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Joined: Jul 12 2016
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Might be worth giving the Ac compressor a tap with a rubber mallet?

Mine has always come off easily with the bolts removed.

The locating dowel is only a short little stubby thing - a few MM high. I can't imagine it would cause the whole compressor to seize in place.

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Joined: Dec 30 2015
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I suspect pixies. The aluminium eating pixies :/

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Joined: Dec 30 2015
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So, guess what? They sent THREE PLY the morons :/
It says single ply on the shipping note, and they asked for a review - so they're going to get one.

I'm trying to route the stupid thick pipe but I've made a cockup. I cut the wrong pipe off the expansion tank :(
Worse, I can't find where the original pipe went because it snapped off when I grabbed it and the other end seems to have run away.

Could anyone tell me where the small (forward) pipe from the top of of the expansion tank runs? I'm hoping I'll have enough pipe left over to replace it. Otherwise I'll be off the road another week :(

I'm looking for diagrams now... but if anyone knows off the top of their head I'd be grateful!

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Joined: Dec 30 2015
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ROFL - it's a breather pipe! No wonder I couldn't find where it ran to :)

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Joined: Jul 12 2016
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Yup, vent pipe. Should have the end cut on an angle.

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Joined: Dec 30 2015
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That's the one :)

OK - it's done! Topped up with coolant and I even re-fixed the cruise control into the bargain. For a Special Needs mechanic, I'm chuffed!
The new top hose is on, but I didn't bother with the hose to the thermostat, it looked like hard work/jacking the car up. I re-used the original pipe without disconnecting it from the thermostat. Let's see how long it is before that comes back to bite me....

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Joined: Jul 12 2016
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I managed to do mine without jacking the car up, it wasn't too difficult.

I think the biggest thing that would have made it easier would have been some light. I was doing it at half 6 in the morning as it was supposed to be going off for MOT. In the dark it annoying trying to route the hose the right way.

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Joined: Mar 22 2016
Posts: 1097

Morat wrote:

That's the one :)

OK - it's done! Topped up with coolant and I even re-fixed the cruise control into the bargain. For a Special Needs mechanic, I'm chuffed!
The new top hose is on, but I didn't bother with the hose to the thermostat, it looked like hard work/jacking the car up. I re-used the original pipe without disconnecting it from the thermostat. Let's see how long it is before that comes back to bite me....

Just treble check you have put any twist on the pipe as it will find a moving part , lol