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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

A useful Engine Modification

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  #1 (permalink)  
Old 18-08-08, 05:45 AM
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Default A useful Engine Modification

On the 2 litre Bristol car which was as good as engineers could produce at
the time, there is one problem which the advent of the motorways has brought to
light, that is high temperature air trapped under the bonnet. The answer to
this would be to put some vent holes in the bonnet forward of the fire wall,
however, this would spoil the look of the car.
Since I tend to do some long high speed runs in my 401 (100B2 engine) London
to Glasgow (400 miles) etc.
things use to become very hot in the engine dept. To counter this I fitted
an original Bristol oil cooler, not that good as it was constructed with 1/2"
dia round tube so the hot oil passed down the middle of the tube, but it was
original and did help but I needed to do one more thing. that was to stop the
hot air passing into the engine.
I managed to find at an autojumble a plastic moulding from a VW that was
about a foot long tube with two oval ends which fitted the oval intake hole on
the Volkes air filter perfectly. I cut this in half secured one end to the air
intake with a jubilee clip fitted a length of corrugated aluminium tube to
the round end which I took forward passing the radiator on the left side above
the oil cooler hoses. The other half of the moulding was fitted to the tube
and secured ahead of the radiator thus allowing cooler air to be drawn into
the engine.
This worked fine and was beneficial to the engine, however, one thing I was
not expecting was that there was a drop of 5 degrees in the water temperature
(85 instead of 90f) in view of this I thought it might be of interest to our
friends in Australia where the temp. is slightly hotter than damp old GB.

My regards,
Bellerophon, Chiltern Section
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Old 18-08-08, 08:46 AM
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Default Re: [6 cyl Bristol cars-t-71) A useful Engine Modification

Bellerophon

My 400 has a 100B2 Engine, an 80 degree Thermostat and a
thermostatically controlled oil cooler of a type that I've seen on
other cars. In the midst of this wonderful English Summer it runs at
80 degrees except on long steep hills when it climbs to 85 degrees and
oil temperature never rises above 50 degrees. I've fitted an Overdrive
which gives 75 odd at 3000 rpm and that's about as fast as you'd want
to go because of the noise! Us Bentley owners are used to a trace of
wind noise and little else at those speeds!

Are you referring to very hot weather or are you using a higher
temperature Thermostat?

Ash
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Old 18-08-08, 09:26 AM
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Location: Melbourne, Australia
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Default

Quote:
Originally Posted by Ashley James View Post
Bellerophon

In the midst of this wonderful English Summer it runs at
80 degrees except on long steep hills when it climbs to 85 degrees and
oil temperature never rises above 50 degrees.
That seems like a big differential between water and oil temps?
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Old 18-08-08, 10:13 AM
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Default Re: [6 cyl Bristol cars-t-71) A useful Engine Modification

I don't know, it didn't surprise me because I had a DB5 that had to
be driven very fast for very long distances to get the oil hot. From
I remember the readings were similar.
I've had loads of teething problems after a total rebuild, but the car
seems fast and free revving and what you'd expect. I think it's a good
'un!
Ash
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Old 18-08-08, 05:01 PM
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Default Bristol405 Oil and Water temps

When I rebuilt my 405 some years ago, knowing that I was going to do some continental touring - in particular the Liege - Rome Rally at the height of the Italian summer, I fitted one of Brian May's thermostatically controlled oil cooling systems, and fitted the largest Kenlowe fan I could, still retaining the mechanical fan. I'm glad I did, because temperatures weren't a concern even during really high ambients. The exception was the ascent of the Stelvio pass, where a combination of a fully loaded car, high revs, and, paticularly, low forward speed rendered the oil cooler relatively ineffective and a temp of 120 plus. Water temp went up in concert to about 110 indicated - but it didn't boil. No temp problems on subsequent continental tours. Now, on motorway cruising at 70(ish) the oil temp sits at 70 -85, with water temp 80-90. But I have a rather 'hot' thermostat fitted.

Brian Kidd
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Old 18-08-08, 06:50 PM
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Default Bristol405 Oil and Water temps

it may well be that mine will get that hot when it is used similarly,
so far mine has only done about 800 miles since it's rebuilt. I
suspect mine might be Brian May's oil cooler kit.

I'm quite excited about the car but doing everything I can to reduce
noise levels as otherwise I think long trips are going to be rather
exhausting. I've had new stainless steel floor retaining bolts made
and put felt sealing strips wherever panels are screwed in, I've stuck
bitumastic pads to every single internal panel, I've welded up 29
unnecessary holes in the bulkhead and replaced every grommet and I've
used the best Motor Wilton made with 12mm thick sound deadening felt
underneath it. Most of the noise is now from the exhaust, I'm going to
look for rubber isolators for the main silencer mounting too.

It's a superb driving car and pulls well and I've had the front seats
rebuilt to improve support and comfort, so it's ready to tour once all
the little bugs are eradicated. It's very near now.

Ash
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Old 19-08-08, 11:09 AM
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Default

Quote:
Originally Posted by Ashley James View Post
I don't know, it didn't surprise me because I had a DB5 that had to
be driven very fast for very long distances to get the oil hot. From
I remember the readings were similar.
I've had loads of teething problems after a total rebuild, but the car
seems fast and free revving and what you'd expect. I think it's a good
'un!
Ash
Ashley, I don' think it has anything to do with a good 'un or a bad 'un - a 35 degree differential between oil and water temperatures just aint right once an engine is fully warmed up. How can you have such a big differential when the oil and water is flowing through the same block?

As for the Astons, I've had a DB4 and DB6 and the temp differential was approx 10 degrees when fully warmed up, which is correct. It's exactly the same for the DB5.

regards,
Kevin
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Old 19-08-08, 11:40 AM
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Default A useful Engine Modification

I suppose it's because there's more water circulating round the hot
bits than there is oil and possibly because 30 or 40 miles in this
particular summer doesn't get anything very hot.
The gauges are all re-calibrated so probably a reasonable guide too.

It's a long time ago but I do remember having to drive the Aston at
considerable speed to get the oil temperature up too. It would be
impossible in the UK these days.

I'll keep an eye on it but I don't see a problem.

Ash
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Old 19-08-08, 12:12 PM
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Default Engine Measurements

Kevin & Ash -

It seems logical there should not be a large differential between oil
and water temps, but perhaps the measurements need to be verified
first. I had an Alfa that seemed to be running hot and I chased
several solutions before discovering a bad water temp sensor.

Somewhat related - I've been researching fuel/air analyzers with a
plan to check several cars, including the Frazer Nash in NZ. I'm
leaning towards the Innovate LM-2. The optional "AuxBox" includes a
2-axis accelerometer and other sensors - almost a handheld
dyno. Anyoned with experience with similar units?

Bob

Admin Edit: As this post started a discussion about engine sensors, it has been copied to a new thread titled Engine Measurements and the posts related to this have been moved - see here

Last edited by devadmin; 20-08-08 at 08:55 AM. Reason: Split thread as topic changed
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Old 19-08-08, 01:04 PM
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Default A useful Engine Modification

Ash, I wasn't suggesting there was a 'problem' per se, at least not with your engine, but possibly with a gauge. I did however assume you were getting the engine nice and hot because you said'

"In the midst of this wonderful English Summer it runs at
80 degrees except on long steep hills when it climbs to 85 degrees and
oil temperature never rises above 50 degrees."

With the Astons, I found it was more the length of time it had been
driven that forced the oil temp up, rather than speed. In fact high
speed often made the oil and water temp go down because of the airflow,
I did also have an overdrive on the DB4 and a 5 speed ZF box on the DB6
which helped keep revs down. I find the worst things for any car is
sitting in traffic. Although none of my Astons every overheated even
sitting in traffic on 'hot' days here in Melbourne (34-40 degrees). My
Bristol 411 was always a bit borderline here, until I stuck an air con
condenser in front of the rad, which really pushed it over the edge!

Anyway, it doesn't matter, I just didn't want people to get the idea
that they should expect a 35 degree temp differential on a hot engine.

I wonder what the 'optimum' temp is for engine oil ...
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Old 19-08-08, 01:50 PM
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Default A useful Engine Modification

Right now we're experiencing a balmy 18 degrees and plenty of rain!

My Bentley hates traffic jams especially at Continental Temperatures
and I expect the 400 will be the same.

I think the temperature difference is a climate difference as much as
anything although I expect my oil to exceed 70 degrees on a motorway
in hotter weather.

It obvious to me that Global Warming is driving my oil temperature down!

Ash
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Old 20-08-08, 11:36 AM
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Default Engine Measurements

John -

Thanks for this info. The WBO2 units seem to have the same functions
as the primary Innovate, except the various Innovate units are
measurement and logging only. I'm still surprised about the
possibility of "DIY fuel injection" whereas a "DIY carb" would seem
very difficult.

Bob
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