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Robert Wort
Grand Master
Username: robert_wort

Post Number: 147
Registered: 12-2004
Posted on Wednesday, 16 March, 2005 - 13:32:   Edit PostDelete PostView Post/Check IP

Whilst noticing the possibly bogus thread from an unregistered user, it did remind me that I have on file some info regarding fuel percolation which is quite often confused with vapour lock. The article came from an MG Club's online newsletter so all acknowledgement must go to them. This of course would not affect fuel injected models.
application/mswordProblems with percolation
Problems with Percolation.doc (92.7 k)
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Martin Cutler
Prolific User
Username: martin

Post Number: 56
Registered: 10-2004
Posted on Wednesday, 16 March, 2005 - 13:57:   Edit PostDelete PostView Post/Check IP

Hi Robert,

My MG Magnette does suffer from this, but only occassionally, so I have not bothered to sort anything out. However, I have thought about wrapping the pipes and manifold with some form of lagging to reduce under bonnet heat on the MK VI. Has anybody else tried this? When the motor is hot, the rod to hold up the bonnet is hot enough to hurt. This must be adding to the overall heat generated by the engine.

Martin
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Robert Wort
Grand Master
Username: robert_wort

Post Number: 148
Registered: 12-2004
Posted on Wednesday, 16 March, 2005 - 14:43:   Edit PostDelete PostView Post/Check IP

Yes Martin! They can get Bl*&#y hot can't they?
My Silver Spur (HO4359), is always difficult to start after running on a hot day and although I have lived with it so far, I am seriously thinking of doing something along the lines of the attachment when it returns from the panel shop.As it is an early model, it still has SU's instead of injection so I don't suppose the later ones have this problem. When I do finally have the spondoolicks to get Robert Chapman to convert Charles to LPG, I should imagine that will end the problem anyway (I hope).
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Robert Wort
Grand Master
Username: robert_wort

Post Number: 149
Registered: 12-2004
Posted on Wednesday, 16 March, 2005 - 14:52:   Edit PostDelete PostView Post/Check IP

Incidently, with Mk V1's, Dawns, Cloud's, Silver Wraiths etc. In fact any model with an unpressurised cooling system, it's probably always a good idea to fit and electric cooling fan anyway. It can usually be fitted behind the grille and out of sight so as not to impede on cosmetic originality. And even if it did, in our severe climate it would be worth doing to save the engine, don't you think?
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 640
Registered: 4-2003
Posted on Wednesday, 16 March, 2005 - 21:01:   Edit PostDelete PostView Post/Check IP

Interesting articl. My cars have never suffered percolation, so are not candidates for these mods.

I do have my doubts as well. You can only lag a small portion of the manifolds, and it won't have much effect. Also, overheating old manifolds by lagging them is a questionable virtue. Maybe lagging the downpipes would be useful.

As most of the heat to the carburettors is conductive, surely heat shields would have little effect there.

On the other matter, vaporisation, it is often misunderstood. The part at greatest risk in the system is the line from the tank to the fuel pump, and not the pressurised side of the pump. Once under pressure, the fuel rarely vaporises. Especially on twin exhaust MkVI and R-Type cars it is highly worthwhile to lag the line, particularly where it passes over the RH exhaust.

Of course, a recirculating fuel system is the best, but you need a suitable new pump, pressure regulator and return plumbing.

One very simple aluminium heat shield and air flow deflector which is very worthwhile is the one shown below behind the aerial in the bottom left of the picture. It shields the voltage regulator and cruise control on our T-Series. It reduces the temperature in this region by up to 30C. Electronic devices age more quickly with heat. I have fitted a similar shield over the cruise control ECU on my R-Type: it was subject to radiant heat being close to the exhaust manifolds.

RT.
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Robert Wort
Grand Master
Username: robert_wort

Post Number: 151
Registered: 12-2004
Posted on Wednesday, 16 March, 2005 - 21:13:   Edit PostDelete PostView Post/Check IP

30C? Wow! That's a considerable difference Richard. I'll probably have to rethink my strategy in solving the hard hot starting. It certainly gets very hot under the bonnet on any day. There isn't a great deal of room for the air to escape. Maybe it's caused by something else. Any ideas?
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 641
Registered: 4-2003
Posted on Wednesday, 16 March, 2005 - 21:33:   Edit PostDelete PostView Post/Check IP

Robert,

I hope I didn't mislead you: that's only at the regulator and CC compartment. Radiant heat and hot air flow are vastly reduced.

It improved so much because the small area is now largely separated from the rest of the underbonnet, and you deflect fresh air in there instead. It's not uncommon to have, say, 70C or higher underbonnet with a 20C ambient, so the pickings there are easy.

For other underbonnet areas, there's not muck scope short of scoops etc.

Remember the '70s Jag XJ6s, with their special battery cooling fans and heat exchangers on the fuel lines tied to the aircons ? Even then the batteries only lasted about 2 years due to the heat: much worse than on a Silver Shadow.

On MkVIs and R-Types, York Motors routinely removed all but two undersheets to implove ventilation. Only the brake pedal and brake servo undersheets were retained.
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Robert Wort
Grand Master
Username: robert_wort

Post Number: 153
Registered: 12-2004
Posted on Wednesday, 16 March, 2005 - 22:18:   Edit PostDelete PostView Post/Check IP

No Richard, you haven't misled me.
But as you say, there isn't much there to lag so I really don't think it will solve the problem.

I'll have a good look at it when the car comes back. My underbonnet layout is somewhat different to yours so I'm not sure if the heatshield will work. I'll check it out anyway.

Thanks Richard,
Rob
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Martin Cutler
Prolific User
Username: martin

Post Number: 60
Registered: 10-2004
Posted on Thursday, 31 March, 2005 - 16:58:   Edit PostDelete PostView Post/Check IP

Hi Richard

I'm interested in your comment about removing undershields on the MK VI's. I only recently removed mine, didn't seem to make much difference, (heat rises?) One friend thought that it would work better to leave them on, as it drew the airflow past the block. What do you think?
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 682
Registered: 4-2003
Posted on Friday, 01 April, 2005 - 04:56:   Edit PostDelete PostView Post/Check IP

Martin,

I agree with your implied opinion. I find it hard to believe that the undersheets made much difference. Remember, Yorks did this alone routinely well over half a century ago. Thoughts of ventilation may have been one reason. Huge build-ups of mud and gravel on the shields when driven in the country may have been another at the time. Remember, Yorks designed the chassis welding, as adopted by R-R for the R-Type, due to savage road conditions unheard of elsewhere.

I think that the fan and road speed are the 99.9% influences on ventilation. Mind you, I could definitely say that underbonnet heat has never been a concern to me on my R-Type, nor has engine overheating with a good head gasket, thermostat and clean radiator, especially with a modern matrix.

I assume that the flat heat deflectors bolted to the chassis above the exhausts are still in place, along with the lagged silecer covers held on by large Jubilee clips ?? Otherwise the floor may be getting a little warmish.

RT.
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 683
Registered: 4-2003
Posted on Friday, 01 April, 2005 - 05:13:   Edit PostDelete PostView Post/Check IP

Robert,

Your car of course has quite a different layout from the '72 I pictured.

All SSII cars, and SZ cars until chassis 9533, have the voltage regulator relocated into the boot next to the battery to keep cool, and later cars have it inside the alternator and therefore positively-ventilated when the motor is running. On SSII onwards the CCs have the ECU under the top roll on the top right, and the CC bellows is sirectly above the RH rocker cover until the electric VDO SZ 20,000-series type.

Don't waste your time looking for an application of the shield I mentioned on your car. It's only useful on cars before SSII.

RT.
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Martin Cutler
Prolific User
Username: martin

Post Number: 61
Registered: 10-2004
Posted on Friday, 01 April, 2005 - 11:51:   Edit PostDelete PostView Post/Check IP

Hi Richard,

The heat deflectors under the floor are inplace, I fitted new ones when the stainless steel exhaust was fitted, nice and shiney aluminium to help reflect the heat. The original silencer covers had rotted away with the remains of the silencers, so new heat deflectors where fitted above the silencers as well. I still fitted 4 silencers, however much lighter in stainless, and it now sounds as a Bentley should. Big improvement in torque as well.

Marty
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Richard Treacy
Grand Master
Username: richard_treacy

Post Number: 685
Registered: 4-2003
Posted on Friday, 01 April, 2005 - 22:20:   Edit PostDelete PostView Post/Check IP

Martin,

Glad to hear that you now have a stainless steel exhaust system. You will never regret that decision.

Now you can forget about decaying mufflers and pipes forever.

RT.