Looking for a 409 engine bonnet-compatibility?

[pasini s]

Nice anecdote, Stefan😁 but nowadays we face a hotter climate and denser traffic in long immobile queues in the scorching sun, that's where my 409 showed that problem.
The late Martin Barnes once told me that the early V8 Bristol's up to the 411 suffered of serious overheating problems in Central London traffic due to a combination of so much heat generated and preserved in those massive V8 iron blocks and the very narrow engine bay...
Cheers
Stefano

[Roger Morrall]

Stefano

Sorry to hear of your problems. Here are some thoughts re bonnet compatibility and overheating in general

1) May I suggest contacting Dr Stefan Cembrowicz, the Chairman of the Bristol Owners Heritage Trust ,who played a significant part in the rescue of various body bucks when Bristol cars assets were sold during the final liquidation, with a view to discovering if he knows whether separate bucks were created for 407, 408, 409 and 410 or an existing buck modified. If for example an entirely new buck was created during this series comparability would probably be lost, but if there was only one buck that was modified (forward of the bonnet) compatibility seems likely.

2) Graeme Payne at the Classic Bristol Parts Company may also know know about compatibility even if he doesn’t actually have a second hand bonnet in stock. Bristol cars services tended not to throw anything away and anything potentially useful was salvaged and put aside

3) Some panel beating may still be necessary to ensure a good fit, that’s how it was done originally

4) It seems likely that most of the extraneous heat under the bonnet actually emanates from those horrible cast iron exhaust manifolds rather than the block itself. The former are tucked up right up under the cylinder heads and there is simply nowhere for the vast amount of heat they generate to go when you’re stuck in traffic, even though the block itself is still cooled by the radiator. I went for broke £’s wise when I owned PEU186F having had a lot of other trouble with them and went for SLJs magnificent tubular manifolds. I perceived (and these are only my perceptions, they’re not scientifically proven) a significant drop in under bonnet temperature alongside a worthwhile improvement in performance - it felt as though the engine had previously been stifled by the cast iron manifolds. It might well be possible to wrap SLJs manifolds with insulation as they are fitted which should further improve matters as far as temperatures are concerned.

5) if you still have the original Carter carburettor also be aware that the float needle valves wear and leak over time which results in the carburettor bowls overfilling, particularly when you’re idling in traffic, resulting in an over rich mixture and a stall. The hotter the air temperature the richer the mixture will be. Suspect this as a potential issue if the idle needle valves have to be screwed at all far in (from memory once I’d fixed this issue the I found to my surprise that the engine idled most happily about three turns out) or if there is a tendency to fail pick up cleanly from idle.

[dwomby]

Originally Posted by pasini s

....................... so much heat generated and preserved in those massive V8 iron blocks and the very narrow engine bay...
Cheers
Stefano

I have always thought Bristol should have changed the engine bay side sheet metal instead of sitting those V8s in the narrow space designed for the Bristol engine. Did they eventually do that on the later cars?

David

[Kevin H]

Before cutting a bonnet to create louvres I would suggest improving the engine cooling system. The original configuration of electric fans (or a single fan on the 409) mounted six inches in front the radiator, albeit in a cowling, seems inefficient by modern standards.

I would suggest replacing the original radiator with a thicker, higher performance radiator and mounting modern fan or fans directly onto the front AND rear of the radiator - with the rear fans designed to pull rather than push air. This will both improve engine cooling and get more air flowing through the engine bay. Obviously removing the original cowling and fan (or twin fans on the later V8s).

[DODD]

I read these postings with interest. I have considered, all be it briefly on occasions, about installing louvred vents in the bonnet of my 410 but for obvious aesthetic reasons I couldn’t and wouldn’t bring my self to disfigure the looks of that long elegant bonnet.

In my opinion the size of the engine bay in a 410 is just about suitable for a straight six but Bristol managed to shoehorn a V8 inside and yes, it looks and is very impressive. Those of you who do maintenance on your car will know how fiddly it is just to change the spark plugs!

David is absolutely correct in his posting, whereby he notes that Bristol should have changed the side sheets in the engine bay. Let’s be fair, the 410 wasn’t the first model to house a V8. I am sure with a little thought it could have been designed more user friendly to take into consideration the trapped hot air in the engine bay.

When I stand back and look at the bonnet of my 410 on a sunny day, I can see a slight bloom in the centre where the finish on the paintwork has changed. This is due purely to the heat from the engine bay not being able to escape once the car has stopped and the engine turned off.

For a long time I have been going to replace the radiator on my car. My car has always had a tendency to get very hot in standing traffic, necessitating the use of the override switch for the cooling fan before the thermostat cuts in and turns it on.

This has very recently come to the forefront of my projects on the car. I have recently installed an independent ATF oil cooler, this has left the existing oil cooler in my radiator defunct.
I currently have a new radiator on order with a slightly thicker core. Additionally, I have purchased a new very high performance 16” cooling fan (the largest and most powerful I could find) and fitted it to my existing radiator while waiting for the new one.

I agree with almost everything Kevin noted in his posting, except having a fan on both the front and rear of the radiator. I had a brief discussion regarding this very point when talking with a specialist cooling fam manufacturer, asking his advice. Unfortunately, they no longer fabricate for the aftermarket sales but nevertheless he shared his knowledge. Basically, having a fan on both sides can give other issues insofar as they must operate at exactly the same speed at all times, the blades must also be the same and positioning has to be considered very carefully and that’s before taking into consideration any voltage irregularities between the fans. All in all he advised me against it; apparently, in cooling fan design for cars, Amps are King.

None of this solves the problem of heat build up in the engine bay once the car stops and the engine is turned off. Unless you fit a thermostatically controlled override switch to the fan, which personally, I wouldn’t do.

As an afterthought, If the bonnets on the 407,8,9 and 10’s are all the same, it might be worth considering having a batch of fibreglass units with louvres manufactured!

Brian

[Kevin H]

Brian,

The reason I suggested putting a fan on the rear of the radiator to pull air through, is because I have done that on my 411.

I'd had air conditioning installed in the 411 and once the radiator had a condenser placed in front of it, the cooling system as no longer sufficient. The original A/C installers had bodged the job so as part of a much larger project the A/C installation was re-done and I was persuaded into replacing the radiator and reconfiguring the cooling system. We removed the original fans and cowling and installed the new radiator forward of the original position, with two modern electric fans sandwiched between the condenser and the radiator. Unfortunately this was still borderline in terms of cooling on a 30+ degree day, sat in traffic. So we added a large electric fan to the rear of the radiator; this dramatically improved the cooling, so even on the hottest days the engine will not overheat.

As far as I am aware there was no consideration given to the speed of the front and rear fans, but it definitely works.

We also did away with the original Otter switch for the electric fans, which I believe the 409 also has, and replaced it with a modern variable thermostat which can be set to turn the fans on a little earlier that the original 98 degrees C. We also fitted a separate ATF cooler.

If I was a 409 owner with a borderline cooling system, I'd probably start by just mounting a slim electric fan directly of the rear of the radiator and see what difference it makes. It's a relatively small cost in the scheme of things. You might need to install a relay to power the new fan, triggered from the original fan power feed.

[pasini s]

Hello all,

thanks for your suggestions, all of them very helpful, but I'd like to point out that after I did fit a new set of electric fans behind the newly recored radiator and an electronically controlled thermostat, I never had any problem with the engine temperature. It remained well under control anytime, even during last week's hot queues. My problem is the engine bay heat that makes the carburettor boil and, as a consequence, the engine stalls.

The opening of some louvres on the hood would surely help lower the engine bay temperature, as no obvious exit was provided for this heat. The fact is that all the heat produced in the combustion chambers of the iron-block 318 is enclosed in a nearly completely sealed 'box' that is the 409's engine bay and this heat cannot escape at all.

I'm sure that Roger is right in suggesting to remove those heavy cast-iron manifolds to put in some tubular manifolds would make a significant improvement, but the cost and modifications would be a bit too much for my taste; apart from that, I think that as the manifolds do not produce that heat, they just transmit it, it would not probably cure my problem completely.

My idea of buying a spare 409 hood would be to make some experiments; I'm sure that I could solve the problem with some judiciously studied louvres but I need to try.

Thanks again for your help,

Stefano