Lotus Elan

Thermostat Housing

PostPost by: rgh0 » Sat Jun 29, 2024 12:18 pm

Maybe Ford in their manual copied what they used for the iron head Escorts ? who knows?

The thermostat is a a simple proportional controller ( if you dont know what that is I can explain it) it starts to open at its rated temeprature and opens further as the temperature increases. The actual operating temperature depends on many variables including radiator size and air flow rate. The Escort had a larger radiator and multi bladed plastic fan so a High temp thermostat maybe give a similar operating temperature to a lower one in an Elan. I dont know all the variables but I can easily understand the directional influences. But if you want a post grad degree level class in heat transfer I am willing to give it to anyone who wants to learn.

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PostPost by: 512BB » Mon Jul 01, 2024 7:58 am

'What year was that workshop manual you are reading from Leslie published?'

1971 and included specs for the Big Valve engine.
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PostPost by: berni29 » Mon Jul 01, 2024 7:48 pm

Hi

Not wishing to get into specifics or right wrongs, is it correct to say that the thermostat (once it has opened) regulates the minimum temperature that the engine will run at, and the fan thermostat (or cooling system capacity for cooling) will regulate the maximum. So to get an engine to run at 85deg vs 90deg (for example) would require a fan cut in at 85deg rather than 90deg. Assuming that the fan actually does have the capacity to bring the temp down to the required level.

It seems to make sense that the cooling system should be able to being the engine down to the same temperature as the opening temperature of the thermostat if required.

All the best

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PostPost by: 2cams70 » Tue Jul 02, 2024 10:24 am

rgh0 wrote: But if you want a post grad degree level class in heat transfer I am willing to give it to anyone who wants to learn.


I'm not smart enough to understand all that Rohan. Only the simple things I can understand - food, drink and that other one that starts with "S"

512BB wrote:What year was that workshop manual you are reading from Leslie published?'

1971 and included specs for the Big Valve engine.


Interesting Leslie. Looking at the Ford manuals they changed the thermostat rating at the time of Mk2 Cortina introduction to the higher rated one. Prior to that the rating was the same as the Lotus figure (i.e for Anglia and Mk1 Cortina). Seems either Lotus got the figure when the engine was originally developed and Ford changed the specification later and Lotus didn't pick up on the change, there's a mistake in the manual or there is a technical reason why the Ford application for the Lotus engine is different to the Lotus one. You may be correct that the Lotus application is different because there's probably less airflow around the engine with consequent implications on fuel vapourisation, poor hot starting, etc. In the case of Ford the Lotus and regular engines all have the same thermostat.

Further to Rohan's comment - it does appear that the thermostat "rating" as such is a somewhat of a vague figure. The specs quote a start of opening figure and a fully open figure. When you say you've installed a 78C thermostat I believe it means it starts to open at 78C - what the set point is that it regulates around who knows?? Presumably it's at a figure somewhere midway between the start of opening and end of opening figure??
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PostPost by: Sadbrewer » Tue Jul 02, 2024 5:08 pm

Just to add...back in the day at least the wax operated thermostats weren't precision pieces of kit...we were in the motor trade and my old man possessed an accurate mercury high temp thermometer. He'd drop thermostats and temperature probes into a pan on a gas ring and bring them up to temp to double check the performance.. and they were often well out from what was expected...it seems like a lot of trouble to go for a cheap item, but I remember he did it on every Hillman Imp or badged clone that had temperature issues as they weren't an easy car to work on.
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PostPost by: Phil.C60 » Wed Jul 03, 2024 7:41 am

Just my two penyworth, and I defer to Rohan's better knowledge than mine. I have always been under the impression that wax type thermostats are always rated at their "crack temperature" and the fully open temperature is around 5* above that, so full flow through the radiator is not achieved until then. For a 74* stat this means around 79*, and guess what Two Cams, that's exactly what happens with 512BB Leslie's Elan, and also with mine. With a 78* stat his ran at 85* and mine with and 82* stat ran at almost 90*. With regard to which is correct, my 1970 manual lists a 78* stat in the specifications section at the front but with a note saying: "See Section K". Section K states: "The current practice is to fit a thermostat which has an opening temperature of 78*C. However, where climatic conditions dictate it may be advisable to fit an alternative; a 71* thermostat is available for use in hot conditions and a 88* for very cold conditions"
You pays your money, and....you use whatever gives you the controlled temperature you want. My Elan is unhappy above 85* and is obviously less "sharp" so the 74* stat I have works for me. Engine wear clearly was not an issue for the factory with a 71* stat, so i don't suppose it will be with my 74* one. And before someone asks, yes, my heater works just fine.
YMMV,
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PostPost by: 2cams70 » Wed Jul 03, 2024 8:49 am

I always ran the Ford specified thermostat in my Escort Twin Cam with no issues whatsoever even in Melbourne's hot summer climate but yes the Lotus application for the engine is different. Personally I'd just stay with what the manufacturer (in your case Lotus) recommended at the time unless there is hard evidence that you need to use something different as the chances are that they probably put a bit of thought into why it should be the way it is.

Running a lower temperature thermostat gives the system more "headroom" to cope under transient heavy loads because the coolant temperature at the start of the transient load will be lower than it will be if the thermostat had a higher temperature. It's only a temporary fix however because under a steady state heavy load there will no longer be any headroom left to cope.

Obviously Ford had more real estate available than Lotus to design a cooling system that works properly! It's generally more thermally efficient to run an engine at a higher temperature that a lower one. The engine will also be less prone to oil sludging and cylinder bore fuel wash. Although bore wash is affected more by the cooling capacity of the system. Too big a radiator means longer warm up times and more bore wash.
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PostPost by: 2cams70 » Thu Jul 04, 2024 8:31 am

OMG - out of interest just reading about typical coolant temperatures of a BMW M62 V8 engine. There's a car with that engine in the family. 100c+ is just normal operation. Things aren't a concern until temps reach 117c+!!!. Obviously the temperature gauge is appropriately calibrated otherwise customers would be popping blood vessels.
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PostPost by: Andy8421 » Thu Jul 04, 2024 8:56 am

2cams70 wrote: It's generally more thermally efficient to run an engine at a higher temperature that a lower one.


I thought as a heat engine the power output was driven by the difference between the charge temperature prior to compression and the charge temperature as the exhaust valve opens, therefore the lower the engine temperature and hence intake charge temperature the better?
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PostPost by: 2cams70 » Thu Jul 04, 2024 9:24 am

Andy8421 wrote: thought as a heat engine the power output was driven by the difference between the charge temperature prior to compression and the charge temperature as the exhaust valve opens, therefore the lower the engine temperature and hence intake charge temperature the better?


Yes there's many factors involved and it's simplistic to just say "hotter is better". A hotter engine will be more prone to detonation but intake charge air is just that. Depending on the installation you aren't going to get a lot of pre-heating of charge air just because you run a warmer engine temperature. It takes time to heat air up and the air travels quite fast from the point of intake into the combustion chamber. If you are drawing air in from behind the grille rather than the hot engine bay the temperature of the engine itself (within reason) is unlikely to make much of a difference.

There were many experiments with ceramics during the 90' to try and get engine temperatures higher. Nox emissions killed that.

It's all a balancing act and perhaps Lotus would have increased the running temperature of the engine if the cooling system had sufficient capacity. I certainly would not be using any lower rated thermostat than you need to however. Getting rid of heat is getting rid of energy that could be released elsewhere other than the cooling system.
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PostPost by: rgh0 » Thu Jul 04, 2024 11:21 am

I love these well educated discussions on engine thermodynamics but I dont have the energy to respond in detail. My only comment is that the Elan has limited radiator capacity and a poorly designed fan either mechanical or electric in later cars. A lower thermostat opening temperature helps keep things in control and the actual operating temperature in an accptable range.

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PostPost by: 2cams70 » Thu Jul 04, 2024 12:33 pm

rgh0 wrote:I love these well educated discussions on engine thermodynamics but I dont have the energy to respond in detail. My only comment is that the Elan has limited radiator capacity and a poorly designed fan either mechanical or electric in later cars. A lower thermostat opening temperature helps keep things in control and the actual operating temperature in an accptable range.

cheers
Rohan


I think we basically agree but I'd add that you are not doing yourself any favours by using a thermostat lower rated than you need. An engine operates on the basis of a big explosion in an enclosed cylinder. If in one engine the walls of that cylinder are cooler than another engine all else being equal you'll have more heat being transferred through the walls of the cylinder into the cooling system on the cooler running engine versus the hotter one. That is wasted heat that is going into the cooling system rather than contributing to the big bang explosion inside the cylinder. That's a simple explanation of the effect (never mind oil sludge and other potential issues).
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PostPost by: mbell » Thu Jul 04, 2024 9:43 pm

2cams70 wrote:OMG - out of interest just reading about typical coolant temperatures of a BMW M62 V8 engine. There's a car with that engine in the family. 100c+ is just normal operation. Things aren't a concern until temps reach 117c+!!!. Obviously the temperature gauge is appropriately calibrated otherwise customers would be popping blood vessels.


M62tu owner. It's an interesting engine in that respect, it has a 110 degree thermostat but also a heater element in the thermostat unit. So under load the ECU enables the heater that causes the thermal to open more lowering the engine temp back towards 90 for better power.

The thermostat are known to fail but also is everything in a m62tu engine cooling system. Basically have to replace entire system every 60k miles to be sure of reliable operation.
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PostPost by: 2cams70 » Fri Jul 05, 2024 12:16 am

mbell wrote:
2cams70 wrote:OMG - out of interest just reading about typical coolant temperatures of a BMW M62 V8 engine. There's a car with that engine in the family. 100c+ is just normal operation. Things aren't a concern until temps reach 117c+!!!. Obviously the temperature gauge is appropriately calibrated otherwise customers would be popping blood vessels.


M62tu owner. It's an interesting engine in that respect, it has a 110 degree thermostat but also a heater element in the thermostat unit. So under load the ECU enables the heater that causes the thermal to open more lowering the engine temp back towards 90 for better power.

The thermostat are known to fail but also is everything in a m62tu engine cooling system. Basically have to replace entire system every 60k miles to be sure of reliable operation.


Ours has 230,000km on the clock and as far as I can tell radiator, hoses etc are all original. Thermostat has been replaced at some stage. Cooling system so far is fine but timing chain tensioners and that masterpiece of german engineeering the ZF 5HP24 transmission - aargh!!

I doubt the thermostat is lowering the temperature under load for more power. It's more likely to be doing it for thermal management reasons to protect the metal parts from becoming too hot under high loads. Admittedly I haven't looked into the details as to how it works. They must have thought though that raising the temperature was good for a reason because they have obviously put a lot of money, time and effort into developing such a system
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PostPost by: mbell » Fri Jul 05, 2024 10:49 am

2cams70 wrote:Ours has 230,000km on the clock and as far as I can tell radiator, hoses etc are all original.


Got mine at 108k miles, now about 203k. Within the first year the top hose failed, had that replaced along with new expansion tank. (New expansion bottle failed very quickly due to manufacturing fault so had to pay for genuine bmw one)

The water pump failed a few months later. Then a few years after that the bottom hose failed. Also had the secondary water pump fail. It's had a radiator replaced within first few years of it's life.

A couple of years ago I fitted new houses, water pump, thermostat, fan clutch and fan, expansion tank and belts/tensioners.

The car has didn't it's while life in Texas so quite a harsh environment for cooling systems with a lot of plastic. Not sure what your climate is like but it's find it surprising if cooling system is completely original on your car.

2cams70 wrote:I doubt the thermostat is lowering the temperature under load for more power.


I've read on Internet that it's about power but I wasn't there when they designed it, so who knows. The heater is certainly there to let the ecu have some control over opening the thermostat more.
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