The Triumph Dolomite Club - Discussion Forum

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 Post subject: Cooling system pressure?
PostPosted: Wed May 02, 2018 3:07 am 
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The book says a 13 lb/square inch cap for a Sprint cooling system.
Do any of you have any knowledge / experience of using a lesser pressure cap? Say 7 lb/square inch?

I have a mate with a very nice TR7 who runs 7lb and he's been trying to "educate" me saying that the slightly lesser poundage has virtually no effect on cooling a system that's in good order.....
AND reduces the likelihood of failures just that little bit. His TR runs just fine with "normal" temps.

I'm keen to have your advice on this.

Thanks & Cheers,
Rob

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"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it". HENRY FORD
1915 Ford "T" Speedster (Evangeline), 1921 Ford "T" Tourer (Anastasia), 1955 Zephyr 6 (Purdey), 1975 Dolomite SPRINT (Daisy), & a couple of moderns.
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PostPosted: Wed May 02, 2018 5:53 am 
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If you have the plastic expansion bottle, it may not be up to pressure the cap says. There is a height discrepancy between the sealing faces on the bottle. Best thing to try if you have a pressure tester/pump is remove the pipe from the bottle and pressurise the bottle and cap together and see what pressure the cap blows off at. It may be around 10psi already. Personally I would opt for the higher pressure system as it should hold water for longer, and higher pressure means less boiling (until it leaks out of course)

Tony

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PostPosted: Wed May 02, 2018 6:26 am 
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Thanks for answering Tony.
I have the steel expansion tank on my car.
The reason I asked is because I mentioned to this friend that coolant is seeping out the side of the head gasket, under the inlet manifold.
Its seeping from next to cylinder #3 (and I suspect #2) I have a couple of valve cover gaskets coming and as soon as they arrive I'll re-tension the head. His suggestion was to reduce the pressure in the system.
I've noticed from some old forum photos that there is a "blind" in the water jacket in those spots.
Does anybody have any advice on this? Is it a common thing in Sprints? If so what is the usual fix? I don't want to go to all the trouble of replacing the head gasket, facing the head etc; unless I really have to.
Thanks again & Cheers,
Rob

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"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it". HENRY FORD
1915 Ford "T" Speedster (Evangeline), 1921 Ford "T" Tourer (Anastasia), 1955 Zephyr 6 (Purdey), 1975 Dolomite SPRINT (Daisy), & a couple of moderns.
Member #2018011


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 Post subject: Okay........
PostPosted: Wed May 02, 2018 8:26 am 
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Depending on it's age, the TR7 will have a different cooling system to an 1850 or Sprint.

Dolomites have an arrangement which is, by definition, neither an expansion tank or a header tank,
said Dolomite tank being the weakest link of its cooling system.
TR7s had header tanks, albeit plumbed into the top of the radiator
(it is better to plumb into the bottom hose).


It is easy enough to fit a header tank to a Dolomite.
Image



If I was you Rob, I would do this after replacing the head gasket......




Ian.

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PostPosted: Wed May 02, 2018 10:33 am 
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Thanks Ian,
Its much appreciated.
Rob

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"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it". HENRY FORD
1915 Ford "T" Speedster (Evangeline), 1921 Ford "T" Tourer (Anastasia), 1955 Zephyr 6 (Purdey), 1975 Dolomite SPRINT (Daisy), & a couple of moderns.
Member #2018011


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PostPosted: Fri May 04, 2018 1:14 am 
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The lower the pressure you maintain a sealed cooling system under, the lower the boiling point will be. For example at 7psi water boils at 113.4C, but at 13psi, that rises to 119.6C. In 'normal' use that is unlikely to matter, but it does lower the reserve you have to cope with times when the cooling system is stressed. Various factors, especially when in combinations will potentially put a cooling system under stress, these include high ambient temperature, increased workload (long uphill roads), higher engine revs, stuck in traffic (reduced airflow through the radiator)etc. Higher altitude will also reduce the boiling point. I think you would have experience that when driving over the ranges!

Adding antifreeze (50% ethylene glycol) not only lowers the freezing point, but raises the boiling point to 106C (at atmospheric pressure). Good, but unfortunately that mixture has a lower heat transfer rate than pure water so while it boils at the higher temperature, it also takes less heat from the engine and loses less from the radiator than the same volume of pure water does. Thus the coolant may well get to its boiling point faster.

Depending on your climate and the risk of the car being exposed to freezing temperatures, or if the car and cooling system are frequently being put under strain, you may be better to just use pure water and an additive that has both a wetting agent (that will improve heat transfer even more) and the required inhibitors to avoid corrosion within the head and block. Latter is especially important with a cast iron block and aluminium head. The most commonly used product is RedLine's 'WaterWetter'. I've used that for years when racing and also in one of the road cars, but my cars are kept in a garage/ barn and in Auckland we only get a couple of mild frosts a year. Incidentally the race car is also fitted with a pressure gauge on the cooling system and it never gets close to a pressure where it will boil.

All three of my Sprints have thermostatically controlled electric radiator fans, as I know yours has, but mine are powered through the always live circuit as opposed to the ignition controlled, therefore they continue to run until down to temperature after the engine is stopped. While the main effect of the fan is on the radiator, there is still considerable effect from air circulating around the engine bay which helps to reduce the risk of localized boiling of coolant in the engine.

I would stick with a standard 13psi cap, but also perhaps have the system pressure tested. As Tony says, if your system has any leaks and can't maintain it's designed pressure, that will not be helping. I run a 77C thermostat (as that too gives some short term extra reserve cooling capacity against the standard 82) and have found in 'normal' running, the coolant/engine temperature is in the range 80-85C. I moved away from the standard Dolomite temperature gauge and now only use ones that tell me what the temperature actually is in degree C. One of those cheap hand held infrared temperature guns you can buy on ebay is also a good addition to a toolkit for a Sprint!

Hope some of this is of help

Geoff


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PostPosted: Fri May 04, 2018 3:35 am 
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Quote:
Hope some of this is of help
Geoff
ALL of it helps Geoff.
My "Thanks" in Bucketsfull.
Rob

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"When everything seems to be going against you, remember that the airplane takes off against the wind, not with it". HENRY FORD
1915 Ford "T" Speedster (Evangeline), 1921 Ford "T" Tourer (Anastasia), 1955 Zephyr 6 (Purdey), 1975 Dolomite SPRINT (Daisy), & a couple of moderns.
Member #2018011


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