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MG MGB Technical - thermostat temp

Moving on to setting the engine up now. Got a shock with the level of pinking with a tankful of standard BP at the w/e. Previous Texaco hadn't been pinking but there may be other issues so will start setting up at at the beginning.

A quick question,

74°, 82°, 88° were specified for different engine numbers and markets yet the engine and rads were all similar. What do you use?
Rich

Rich - I use the 88°C (190°F) year around on our 66 MGB with a 18V engine in it. The temperature comes right up to 190°F and stays right there unles it is a very hot day (100°F or greater) and I am pushing the car really hard up a steep grade, then I can get it up to 212°F - 220°F. It goes right down to 190°F as soon as the road levels out. Cheers - Dave
David DuBois

Very few, if any agree with me on this one but here it is. In the warmer months I run a 165F (74C) in my 18G engine. That is the original factory spec for the 18G. Now I know that its too cool for efficient combustion but it doesn't stay at 165 for long. Gradually, it creeps to just under 180. Now when I'm stuck in traffic or have hill climb issues I have and extra 10 to 15 degrees of insurance. In the colder months, I run a 190 for cabin heat. Not saying its the right way or the best--just what I do.

Paul
Paul Hanley

Paul,

Sounds good to me as protecting oil from high temps when it will thin and burn off, the downside would be maybe short trips when you want the oil warm.

Paul
Paul

Having been in the motor game a long time I have pulled many engines down and I have found that engines fitted with low temp thermostats (or worse no thermo)have a lot more wear in the front cylinders than the rear cyls. This is because the cool coolent from the the radiator hits the front cylinder or cyls in a V8 first and then heats up as it moves back. I am not talking a little more wear I am talking maybe three times the wear. I would never go below 180*, and use 190* myself in my supercharged B with no heat problems, and it can get pretty hot in OZ. Denis
DENIS

Keep in mind that older cars have colder thermostats in part because old oils couldn't take the heat. Modern oils are much superior to anything available when our cars were new. So I agree with Denis -- I run a 195ºF tstat year-round. Ambient temps here in the summer are usually in the 90s and often over 100ºF. I have no overheating problems.....
Rob Edwards

Paul H - Your observation that even though using a 165°F thermostat in the summer months, the engine will heat up to 180°F illustrates the fact that the thermostat has very little effect on the upper temperature that an engine will operate at. It only sets the minimum temperature where the engine wil operate. I suspect that 180°F is the temperature that the B series engines like the best when they are in good condition. Those of us using 190°F thermostats are forcing the engine to run about 10°F higher. Whether this is good or bad, I don't have the engineering knowledge to say, but everything that I have heard coincides with what Denis of Austrailia stated regarding excessive wear. In all the years that I have had MGs (both MGB and TD) I have not seen any ill effects of operation the engines with a 185°F - 190°F. Cheers - Dave
David DuBois

Engines are more efficient the hotter they run so I would opt for the 88 degree stat.
Chris at Octarine Services

The boiling point is not 212f for a pressurized system. Each pound of pressure cap tension produces about a 3degree F boiling point increase. e.g. a 7 lbs pressure cap increases the boiling point by 21f.

Anti freeze also increases the boiling point depending on the ratio of anti freeze to water. Take a look at the bottle, it will probably show the temperature ratings at different mixing ratios and pressures.

With a later model radiator running 50% antifreeze and a 14 lbs pressure cap, the boiling temperature moves up into the high 200f range.

There are issues before boil over however: 1/ Anti freeze raises the boiling temperature but does not carry as much heat as does water. 2/ at temperatures below boiling there can be hot spots in the engine where the water will be heated to a boiling temperature even thought the system as a whole is below boiling. This problem is usually encountered in hi rpm hi load situations where there is both a hot spot and a low pressure area from the speed of the flow of the coolant.

In No California temps rarely drop below the low 20f range. My engine temp never goes over an indicated 212f. To get adequate freeze protection, corrosion protection and max heat carrying capacity and heat transfer, I run approx 25% to 33% anti freeze and a water wetter additive, the rest tap water. Some people in the colder areas use more antifreeze in the cold season and less in the summer to get the advantage of the greater heat carrying capacity of water over antifreeze during the hot season.

Overheating is to some extent a self correcting situation. (or a stable system) As the coolant gets hotter, the difference between the outside ambient air temp and the coolant temp increases. Because of that differential there is more effective cooling per square inch of radiator surface. A hot radiator will lose more btu's than a cooler radiator. An engine creates the same heat load (btu output) whether it is hot or cold weather.

One of the advantages to running higher engine temperatures is that a smaller radiator can be used.

Modern oils handle these temps. Oil coolers were dropped by the factory in the '70's even though they moved to smaller sump capacity and much hotter running smog control engines.

Running cool and having condensation in the oil from short trips is a bigger risk than running the engine at higher temps with fear of oil breakdown.

Barry

Barry Parkinson

My thinking was the summer heat: the engine temp goes where it wants to be, in straight and level driving, within a few minutes regardless of termostat heat range. But I'm assulting the Rockies twice this summer in July heat. I rationalized that at least on the downslope of a mountain, the engine goes back down to a low stress mode, cools off to 165, and then you have another mile or two of high speed running--upslope before she starts running hot; maybe enough time to crest the next hill. And we'll be crossing dessert.

But what has me rethinking it all and going with the 190 and perhaps a 14 lb cap instead of 7, is the advantage of longer engine life, modern oils formulas, flushed radiator, etc, as you gentleman have so eloquently argued. And I won't have to break the paint on the nuts.

Thanks,

Paul



Paul Hanley

Thanks, I agree with all the replies and have variously thought the same.

A point to clarify first, the stat starts to open at the temp specified but doesn't fully open for another 20°F, so it can set the minimum and maximum temp range. It explains how the engine may show an increase whilst being thrashed or after switching off but will seldom go too far and boil; the stat has 20° in hand and just opens a little more.

Perhaps we can't treat a 50's engine like a 90's one. It's a big cast iron lump with no great technology employed with regard to water flow or materials. Todays engines are engineered to run hotter in the interest of efficiency using aluminium and intricate water galleries which respond quickly to the coolant. Many also are OHC with copious oil supplies to the top which take away a lot of head heat. I accept later B engines were run hotter but think this may have been forced on them due to emission regs rather than designed-in.

Anyway I decided to try following the book as far as possible. Today I fitted a 74°C stat, warmed it up for 30 miles then tried resetting fuel and ignition. Ended up with a good improvement in running using another flat rich on the jets and 2° more advance, without pinking on the same tank of unleaded. Did this without switching off, then realised that, when I did switch off, it didn't run on at all :-) I'll be interested to see how it goes next time out.

(PS sorry, long post, car bought in August with 92° stat fitted, no pinking but running on badly despite MGOC anti-run-on valve fitted by PO. I changed to 82° and ditched the a-r-o valve and it was better, then changed again today.)
Rich

Rich,
The thermostat cannot set the maximum temperature if the rest of the cooling system is not up to par. The only thing the tstat can do is to open and hope that it brings the temp down. If the engine is making heat faster than the radiator can shed it (perhaps due to a partially blocked radiator), then the car will overheat -- regardless of the thermostat's temp rating. (And of course the answer there is to fix the cooling system, not change to a different thermostat.) The only thing a thermostat can do with certainty is to keep the engine from running too cold. IOW, it can "enforce" the lower temp limit, but only "suggest" an upper limit.

HTH!
Rob Edwards

Isn't a faulty cooling system a different issue Rob?
There's a 20°F range over which the stat goes from starting to open to fully open. Seeing variable temp within that range (as David and PaulH mention) would be normal. If it went past that range there may be a fault. Rich.
Rich

Yes, a faulty colling system is a different issue, but too many people believe that switching to a colder thermostat will rectify the fault. Environmental factors can come into play as well. So the thermostat can influence the max temp, but not set it.
Rob Edwards

OK, good point Rob, let's take it that mine's fine and if I stick in a 74 it runs at that, ditto 82 and 92.

So, which to go for? I'm trying to figure why MG went for 74 when they could have chosen anything. There looks to be 3 votes for 88, 2(?) for 74 and 1 for 92. Barry didn't actually say but it was a darn good post so we'll stick him down for a 92 as well :-)

Oil's a good point but I'm sceptical of "better" quality over here. The 20/50 available seems to be cheap stuff, often without an SAE grade even, or deliberately old tech sold as "Classic" at inflated prices. The oil companies must be loving it given that lubricating oil is the most unwanted part of crude refining.

Unipart Green 20/50 SF and Delphi 20/50 SG seem good but both those specs are late 70s/early 80s so hardly hi-tech. Other "old" oil has junk like seal swellers in it and sold for old bangers rather than old beauties.

Rich

Rich

I used to run a 190 stat year round and switched to a 165 last summer. I agree with the previous poster that there is a 15 degree protection gap and, the stat runs wide open most of the time and the gauge (actual temp) is usually 180-185.

Last winter I did not swap out the stat because there was sufficient heat: I had replaced the heater gasket and cleaned out the heater box.

rn
RN Lipow

http://www.gi.alaska.edu/ScienceForum/ASF7/747.html

http://www.minimania.com/ArticleV.cfm?DisplayID=1506&SCatagory=COOLING&DisplayType=Calver%27s%20Corner&CarType=

Water temps can be run around 120°C: running these higher temperatures means less airflow through the radiators, thus improving aerodynamic performance but this is traded against known power loss and with the abilty to redesign car to take advantage of the aerodynamic performance. For a B?

BMW do not recommend running even a good quality mineral at over 130c sump temp, synthetic oils especially ester based can withstand higher temperatures but this is stll not ideal but are unlikely to be stressed. The average oil temp at bearing is 150c and sump temps will possibly range from appox 1.2 to 1.5 above water temp.

If US oil- it is difficult to souce good quality viscosity improvers which a 20W50 relies upon, and I would not go near a non rated oil, especially as oil is so cheap in US with full add pack.

Paul
Paul

Once again, the point must be made that the thermostat, regardless of the 20 degree range, only limits how cool the engine will run and has no effect on how hot it will get.

One of the most important things, regardless of the engine design, is a consistent operating temp. You want to maintain a temp that does not vary much to avoid thermally stressing the engine. The trick is to find the range that works best for your climate.

I have a '73 B and have run a 192 degree F stat for about 15 years now. Whether it's summer (95-98 degrees F) or winter (30-40 degrees F), my temp gauge varies only from the needle covering the left vertical on the 'N' to covering the right vertical on the 'N'. After testing with a glass thermometer, this variance is only about 10 degrees F. Dead center on the 'N' on my car is about 210 degrees F in the radiator. I run a 7 psi cap and there is no tendency to overheat because the boiling point is raised to about 230 F.

And the proof is in the pudding - I rebuilt this engine in 1980 and have 119 K on the rebuild and consume only about a quart of oil between oil changes.

AND I have real heat in the winter...
Richard Smith 1

There are several articles about cooling system theory and thermostats on Barny Gaylord's site. Look under cooling system.
http://mgaguru.com/mgtech/index2.htm

FWIW, I use a 82 thermostat year round.

Clifton
Clifton Gordon

<< In essence, the thermostat only controls minimum operating temperature within a narrow range, and has nothing to do with maximum operating temperature. The only way to keep the maximum temperature down in the same small range as the controlled minimum is to have such a large radiator as to be constantly overcooled, even with the hottest running conditions. >>

A quote from Barny's site. What he describes in his second sentance is the norm for a competent system in the UK at least. It's not constantly overcooled as, he has just told us, the stat sets the min temp.
Rich

Rich

If UK based a 74c is too low. Oil takes longer to warm up than water and oil really needs 80c plus, and you need to get to this temp and above as soon as possible.

If going back in time check recommended oil viscosity could well be lower than a 50.

Paul




Paul

Hi Paul, All,

Mono 40, 20W/40 or 20W/50 were all specified for temperate climate; there were at least 3 of the latter listed, BP, Filtrate - and the ubiquitous Duckhams Q20W/50 - crikey, was it that long ago? Interestingly, the monogrades were scheduled for 3000 mile changes and the multis for 6000 miles.

All in all an interesting thread and thanks for all the comments. I'm no surer than anyone else but it does no harm to try and understand the original specs does it. I was having problems setting up on unleaded, pinking and running on, which made me dig out the manual and start from scratch.

I moved on last w/e to several hours empirical testing up and down a quiet dual carriageway and finally confirmed the cause back home with the timing light in the garage. In a nutshell, the heavy spring in the dizzy was a little slack. This caused the timing to immediately advance 8° further than it should on start up. Instead of going to static plus 4° auto advance at 600rpm it was static plus 12°!

I didn't realise this initially and, in turn, had retarded 8° which I found by testing had stopped the pinking at lower revs but, of course, the timing was then only reaching 22° at full advance so it didn't want to rev at the top.

The cause was about 50 thou slack on the heavy spring which caused 8° error in a dizzy that otherwise looked fine. A small tweak with the pliers and the spring still looks the same but the curve is now to spec, the pinking is gone, and the engine revs like a demon.

Many thanks to Les and Paul Hunt for the spring and curve info on their sites.

I've taken everything said about the cooling system on board, and have re-installed the 82° stat.

Rich

Rich

Rich,

I occassional wonder about original specs and received some interesting views from a wise mini fan sage, incidentatly they immediately changed 74c thermostat to 78c

( a few extracts)

I did my Engineering training - six years - with BMC - in NZ and in England (Stewart & Ardern, "The Vale" Acton - 1962-63)

The export prototype Mini was my first development project in NZ in 1959
The tragedy of BMC was the lack of funds for refinement and, in the end funds were taken from the very viable Leyland Trucks Division to support the cash hole in the Car Division. However that was long ago and far away

Oil changes on the Mini were done at 1000 miles without fail - but they leaked SO much anyway it probably didn't matter much!
The OCI for other BMC engines was 3k miles max. and Castrolite (20w-20) or Castrol XL (20w-30) were the most common lubricants. Mobiloil Special 10w-30, or BP Visco-static were "not good" in these engines in the 1950-60s!

It is also interesting to note that engine life in cold and hot climates is very similar if the Manufacturers servicing advice is adhered too. Therefore, similar cars starting from a base low (cold) of -25C and +25C will almost always have the same engine life other factors being the same. Does this suggest that the design of the cooling system (for quick warm-up) and the Engineer's designed core temperature have much to do with the engine's ultimate life?



When the Mini came out in 1959 a specially formulated oil was required Duckhams 20w-50. It was the first "heavy" multigrade - 10w-30s had been out for years. You could use the same oil viscosity today in the same engine without an issue of course. We used 10w-30 20w-20, 20w-30, 20w-50 and mono HD oils in BMC "A" "B" and "C" series engines around the world in various markets without problems - as you could today. We got very good engine life at that time.
The '74 MGB I sold a couple of years ago ran well on 15w-50 and 5w-40 synthetics - the 5w-40 wasn't in the Handbook but met the original viscosity "intent" of the Handbook
The engine felt better on the 5w-40 though


the "intent" with the B series engines was to run as I recall 20-20W (Castrolite) or 20w-30 Castrol XL. We also used HD30 oils such as Delo etc. Later this included 20w-50 as these oils became available. We used 10w-30 too and had exceptional engine life with all of these mineral oils if the car was serviced reasonably well. I know of one doing well over 300k miles without work (except for a water pump as I recall)

The availability of synthetic oils changed all this
Paul

Rich, I'm with Chris on this one, both my cars have 88 degree stats and I use a 15lb cap. Both have new rads and run on N all day unless of course you leave it idling whereupon the temperature might rise and run on will then be an issue. This is really minor and best ignored.

I run an Audi A4 1.9tdi so the oil I use is both diesel and petrol compatible. It is obviously highly detergent and considerably in excess of what is required for these old engines. Consumption is negligible.
Iain MacKintosh

Gentlemen,
I have a 180 degree thermostat and 14lb radiator cap. The car is a 74.5 B with an oil cooler. On the ride to work today the temp gauge barely got past C and rose to mid way between C and N only when stopped for traffic just off the highway. Outside temp was in the low forties. The heater was throwing some heat however, (my feet were warm even though the top was down.) The stat was replaced last year so I know that's not a problem. Even with the old stat the temp never got to high above C except in traffic. Could I be getting a false reading from the temp gauge? Or is it running real cold.
John

Could be a false reading, or it could be a bad thermostat. It wouldn't be the first time I've seen parts bad straight out of the box. Have you got a thermometer you can stick in the filler neck to take its temp? Better still would be an infrared thermometer with which you could take the temperature of the thermostat housing. Barring all that, thermostats are cheap. You could try a different one.... Although if it behaved similarly with the previous one, my bet is that it's a false reading.

Incidentally, on some advice I found on the web, I drilled a 1/8" hole in my last one to "avoid subjecting the engine to thermal shock and to allow air to bleed out of the system." That 1/8" hole was enough to make it very slow to warm up in warm weather and to completely prevent it from reaching operating temp in cold weather. I put in a new (undrilled) tstat and it reaches operating temp in just a few miles, even in very cold weather. I'm also using a blanking sleeve as outlined in the Barney Gaylord page cited above.
Rob Edwards

Warm it up from cold whilst feeling the top hose. It should stay cool while the temp gauge rises towards N, then get very hot in a rush as the stat opens. If it gradually warms up with the temp gauge it is stuck open. If you get the rush of heat at a much lower temp on the gauge than N then it is opening too early. I've driven mine in temps down to freezing (and the V8 way below freezing) and never failed to have them running close to N, with the heater on and hot (OK, a relative term, but still plenty hot enough so I have to turn it down).
Paul Hunt

Thanks Rob and Paul, I'll give it the hand check tomorrow morning.
John

Paul, I started the "B" today and, despite almost losing a finger to the fan, held my hand on the top radiator hose while the engine heated up. The hose did not gradually heat up but did get hot suddenly, the temp gauge was only pointing between C and N when that happened. I know the stat is working so could it opening early or is the temp gauge showing a false reading, getting plenty of heat in the cockpit.
John

John
Measure the temperature. A baking turkey type thermometer(if you don't have something better) will do. put the thermometer against the head and then against the top radiator inlet and you will get an idea of the temp of the engine and of the the water exiting the engine.
Barry
Barry Parkinson

John,
If the cabin gets cosy it's certainly the gauge. My GT runs with the needle pointing to just the same spot, a little above "C". I had to get an accurate reading when I fitted an electric fan so I unscrewed the sensor at the cylinder head (no need to drain the coolant) and put it in a pan of 80*c water. The gauge sat at its usual lazy point. For reference, with your cooling system in good order 80*c is about the normal running temp for the water, and 90*c is what you get after sitting in traffic for a while. You may want to start with the water boiling so you can see what "hot" equates to on your gauge.
Steve Postins

I'd agree with checking the engine temp when the stat has opened. Electric gauge, I assume. Try grounding the green/blue at the sensor on the head just enough to see if it reaches H. If so, and the temp is OK, the sensor is probably at fault. If not, then possibly the gauge or the voltage stabiliser (although this would affect the fuel gauge as well) or the connections between them all. It would be helpful if someone with correct indications posted the voltage reading on the green/blue with the gauge showing N (both mine are mechanical). This would probably have to be taken with an analogue voltmeter as the 'voltage stabiliser' actually switches 12v on and off about once per second. It would then be useful to take a similar reading from the fuel gauge showing half a tank. If the readings are similar (hoping that only the markings on the face differ between the two gauges) then one could cross connect them and determine whether the sender or the gauge were at fault.
Paul Hunt

Costco has an Oregon Scientific brand oven thermometer for about $30. It has a remote sensor that can read to 199 C or 199 F (that's as high as the digital readout goes) The readout can be up to 100' away.

Buy your wife a gift. Stick the probe on the top hose and drive around read your actual hotwater temp to 1 degree accuracy. You can get creative and check the head temperature - the carb temp - the oil filter temp- the underhood temperature- trans temp- rear end temp. You could probably use it to check your own temp and read it while 100' away.

Barry
Barry Parkinson

Paul - I believe that you could determine what you are looking for by going to Rick Astley's web site at: http://www.mgcars.org.uk/electrical/, click on instruments and then on the gauges you want information for. Rick has a chart of resistance vs temperature for the temp gauge, so all you would need is the resistance for the heating wire coil in the two gauges. Cheers - Dave
David DuBois

This thread was discussed between 29/03/2005 and 10/04/2005

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