running temp

Discuss mechanical problems here.
Forum rules
By using this site, you agree to our rules. Please see: Terms of Use
Post Reply
robandsophie
Minor Fan
Posts: 106
Joined: Sun Oct 25, 2015 3:36 pm
Location: Sidmouth Devon
MMOC Member: No

running temp

Post by robandsophie »

Hi,

What is correct running temp for a 1098 Minor? I have seen on some threads would be high 80's. My runs at between 70 and 80 quite happily. Does engine temp matter? I have recently replaced the coolant (due to engine out). Took right amount of fluid back in, no evidence of air lock.
Any ideas?
firedrake1942
Minor Legend
Posts: 2942
Joined: Tue Aug 25, 2015 6:07 pm
MMOC Member: No

Re: running temp

Post by firedrake1942 »

Have a look at these posts

viewtopic.php?f=4&t=42087
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: running temp

Post by oliver90owner »

Does engine temp matter?

Of course it matters! Everyone should know that a cold engine under-performs and requires a richer mixture (think here cold starts in winter) and an over-heated engine can be damaged quite quickly. Wear is accelerated at low engine temperatures, water is absorbed by the lubricant at low temps. The list could go on. Loss of coolant occurs on over-heat, among other effects.

Temperatures are optimised by the manufacturer to run efficiently on the fuels available. Petrol engines do not run on kerosene without modified manifolds (and reduced compresion ratio, of course). Merlin engines were cooled by neat glycol, so had a much higher operational running temperature than our usual car engines.

There is always a temperature difference between the hot and cooler sides of a metal casting. In a water based non-pressurised cooling system, the water must not exceed 100 degrees or the water at the interface will boil and cause problems.

So the engines are designed to run at the highest practical temperature witout the internal cylinder head surfaces rising to the point of fuel autoignition or too cool to sufficiently volatalise the incoming charge.

Basic outcome of all this is: run at the highest temperature possible, within the manufacture's specification.
liammonty
Minor Legend
Posts: 1185
Joined: Mon Apr 23, 2007 2:32 pm
Location: Dartmoor
MMOC Member: No

Re: running temp

Post by liammonty »

Assuming the rest of your cooling system is functioning correctly, what hasn't been mentioned is that the temperature it runs at will be determined by the thermostat. These are readily available in different specs - typically 74, 82 and 88 C. 'Correct' is subjective - different thermostats were fitted from new, I believe. People would often fit a 'hotter' thermostat for the colder months, and revert to a 'cooler' one for the summer. I have run an 88 C thermostat all year round with no trouble (I've retro-fitted a temperature gauge), even though some say that this is a bad idea, in reality, the Minor engine is so over-cooled that it is fine. It also gives far better heat from the heater in the winter, and I suspect (as per the previous post) leads to slightly more efficient running. I think that the 82 C thermostat is generally regarded as the best for all-year use, but I can't substantiate that claim. From the temperature you say your car runs at, I suspect you have a 74 degree thermostat fitted. If it bothers you, fit a new one of your preferred rating, but be prepared for fun and games getting the thermostat housing off when you do so!
dalebrignall
Minor Legend
Posts: 2528
Joined: Fri Aug 03, 2007 4:06 pm
Location: stalbans
MMOC Member: No

Re: running temp

Post by dalebrignall »

its horses for courses really , i think 82 degrees is the one thats in most circulation
[sig]5641[/sig]
robandsophie
Minor Fan
Posts: 106
Joined: Sun Oct 25, 2015 3:36 pm
Location: Sidmouth Devon
MMOC Member: No

Re: running temp

Post by robandsophie »

Yes I know cold engine not as efficient,and a over heated engine is ruinous. My point (which I didn't make very clearly) was, does a Minor have an optimum temp I should be aiming for. Thanks to Liam and Dale - 82 degrees seems the ideal and as Liam states I probably have a 74 degree thermostat fitted, so will insert a 82 C - should be fun!
dalebrignall
Minor Legend
Posts: 2528
Joined: Fri Aug 03, 2007 4:06 pm
Location: stalbans
MMOC Member: No

Re: running temp

Post by dalebrignall »

its easy as long as the thermostat housing nuts come undone , if they are rusty a good wire brush on the top and some plus gas a day before
[sig]5641[/sig]
MikeNash
Minor Addict
Posts: 781
Joined: Fri Sep 24, 2004 9:09 pm
Location: Hurstbourne Tarrant, Andover, Hants.
MMOC Member: Yes

Re: running temp

Post by MikeNash »

R&S, a few thoughts..
If you've the standard 4psi radiator cap that'll require a coolant temp of 106C before it'll blow off steam so you've quite a lot of "headroom" available for a higher temp thermostat. I ran a 89C thermostat for years without any overheating even when driven hard with a trailer. (But alas, the thermostat failed recently so I'm on an 82C one like you have fitted, at least for the moment.) However, if you're going to go any higher, e.g. a thermostat that's in the nineties (I'm tempted!) then a reliable temperature gauge becomes important. One of the reasons for the higher temps is that in cold weather when you use the heater you'll find that the thermostat hardly opens at all, which is good news for the small amounts of hot water that go in at the top will emerge into the bottom of the engine surprising cold - not a good thing for the engine at all. Reducing the radiator circulation is then a good thing. Alternatively or in addition, of course, you can block the radiator to reduce cooling airflow.
To Oliver, Merlins used a water/glycol mix. Long ago and far away I read an pre-war RAE test note recommending 60/40 water/glycol mix and the "Lancaster Aircraft Mark X Maintenance and Descriptive Handbook" gives 70/30 for summer flying and 45/55 for winter. Incidentally, the maximum permitted coolant temperature for combat power (i.e. for 5 minutes) is 135C which implies a pressure of at least 30 psi gauge (i.e. about 45 psi absolute).
Yours pedantically, MikeN.
Morris Minor, the car of the future. One day they will all look like this!
oliver90owner
Minor Legend
Posts: 1653
Joined: Thu May 12, 2016 6:33 am
MMOC Member: No

Re: running temp

Post by oliver90owner »

Agreed, Mike. They adopted 70/30 glycol water for production engines in the X version onwards. Prior to that it was 100% ethylene glycol.

Glycol, with a boiling point of near 200 degrees, would need no pressure to operate at those elevated temperatures. Further, a 70/30mix would have a boiling point well elevated from that of water, even at atmospheric pressure, so I very much doubt the system pressures would have been as high as you stated. Of course, at their ceiling operating altitude, atmospheric pressure would be somewhat lower than one atmosphere.

Indeed, the first merlin prototypes were run on evaporative cooling, thus cooling by superheated steam at high temperature.

I was being very 'generalistic' using the merlin engine as an example of different engines requiring different optimum operating parameters.

Remember, raising the coolant temperature in a Minor engine cooling system by 10 degrees is a large percentage increase over poorer operating temperature (low enough to allow water absorption and retention in the oil/condensation in the rocker area, per egs). The designed range is clearly 74-88 typically (but that is only the temperature at which the thermostat operates, of course). Additionally, back in the 1950s some were using water only (draining down at night in winter) or ethyl alcohol based antifreeze, which would clearly depress the boiling point of the coolant below that of plain water!

I cannot remember when glycol antifreeze displaced ethyl alcohol versions, but ethyl alcohol versions were still around in the '60s, for sure. Glycol was relatively expensive because it needed careful buffering to avoid corrosion due to its slightly acidic nature and more acidity as the glycol was slowly degraded by heat, etc.

I can be pedantic, too! Having a scientific working life and a practical agricultural upbringing, as well as being old, all helps a bit.
MikeNash
Minor Addict
Posts: 781
Joined: Fri Sep 24, 2004 9:09 pm
Location: Hurstbourne Tarrant, Andover, Hants.
MMOC Member: Yes

Re: running temp

Post by MikeNash »

Oliver,
That's interesting; I hadn't known that Merlins actually flew with 100% glycol. The change to water/glycol mixes makes me think that the test note I'd read as a lad (about 55 years ago!) was probably part of the case for the change for it suggested that the 60/40 water/glycol ratio was the about the right compromise between the reduced viscosity, which allowed faster flow, and reduced specific heat which reduced heat transfer. Some modern background is here http://www.engineeringtoolbox.com/ethyl ... d_146.html
I see that says that a 70% glycol mix is boiling at 118C unlike 100% glycol, which boils at 197C. The 70% glycol mix is usefully elevated over 100% water but not as much as I expected.

Re the A series engine, it's interesting to see that the glycol ratios we might use say 30% glycol/70% water can raise the boiling point to about 105C on its own without pressurisation. The latter adds more, so p'raps we then boil at about 110C. Even more headroom! (That's if our antifreeze has the same characteristics as Glycol, of course.)

Regards, MikeN.
Morris Minor, the car of the future. One day they will all look like this!
Post Reply