Lotus Elan

Otter Switch

PostPost by: terryp » Thu Sep 10, 2009 5:13 pm

Hello
I've fitted my Kenlowe + overide switch and everything is OK but I did wonder wouldn't it be great if the fan switched on at the right point
Firstly then if my thermostat is 75 degrees , what is the right temp to switch the fan?
Secondly would the below fit my standard plus 2 radiator?

Thanks
Terry
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PostPost by: alexblack13 » Thu Sep 10, 2009 9:18 pm

The engine likes to run at around 70 - 75 deg. Try setting your switch to close at around the 80 mark.The more cooling the better methinks.

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PostPost by: memnon » Thu Sep 10, 2009 9:26 pm

I believe 72 is the optimal water temp for engines... I'd set it to that, how many opinions are you after ;)
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PostPost by: alexblack13 » Thu Sep 10, 2009 9:40 pm

:lol: :lol: Yep I have a 72 thermo' fitted. Temp rocks from about 75 -80 on the guage. My electronic unit set to switch at around the 80 mark keeps it all under control nicely. Even at that setting I find my fan runs quite a lot in town.

Stand by for at least another 10 or so opinions. :lol: :lol:

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PostPost by: 69S4 » Fri Sep 11, 2009 6:44 am

alexblack13 wrote:Stand by for at least another 10 or so opinions. :lol: :lol:
Alex B.... 8)



Well here's the first of them. I'm running at 84 /85C on the open road with the fan holding it at around 90C in traffic.

If you go back through the archives though you'll probably find an advocate for every single degree between 72 and 100. The lower end of the scale does seem attractive in that you've got further to go before overheating panic sets in but in colder weather the heater is virtually non functional.
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PostPost by: terryp » Fri Sep 11, 2009 6:51 am

Too be honest I don't go out in the cold, wet , windy, foggy, dusty, dry, humid, hot, dark, so the heater is better not working! :wink:

My engine does seem to run better at a lower temp. I've bought a 75 thermostat as that was the lowest that TTR had , (Susan Miler had a 76, not sure about PM)
Would a 72 or 71 be better as I could try to source from the US? :shock:

I'm rather confused about the otter switch , but I'm lead to beleive that the temperature isn't that accurate on them anyway, Is there a rule of thumb for a certain number of degrees above the thermostat?

Thanks for the replys!!!! :D

Terry
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PostPost by: richardcox_lotus » Fri Sep 11, 2009 7:27 am

Based upon my dodgy memory, I thought you'd like to set the fan to come in at roughly 10 degrees more than the thermostat setting. Having said that, I didn't think Otter switches were adjustable ? I also don't think they are particularly reliable (I'm on my 3rd) and there is an additional debate as to whether they are sited in the best place anyway (A topic that's been discussed on other threads - notabley ones relating to electric water pumps)

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PostPost by: terryp » Fri Sep 11, 2009 11:39 am

So its back to the manual overide switch then!
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PostPost by: stuartgb100 » Fri Sep 11, 2009 3:19 pm

Terry,

According to my notes, the best Otter switch for the twin cam is rated at 78 deg C.
Its' accuracy is +/- 3 deg C (they say).
I too prefer to run at 72 degrees and have found a thermostat

THERMOSTAT Quinton Hazell QTH 167 Factor Nib on outer flange needs to be flattened. 72 degree rated. Lotus used 3 official thermostats: hot climates - 71degC/160degF, temperate - 78degC/173degF, cold climates - 88degC/190degF.

Having said all of that, I too preferred the adjustment that the Otter does not have, so moved to Kenlowe soon after.
Have now moved on to a fan controller mounted in the top hose.

Be careful not to set your cut-in speed too close to the thermostat setting, or you'll end up fighting the thermostat.

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PostPost by: terryp » Fri Sep 11, 2009 8:48 pm

Stuart
Have you the Pacet type hose switch or a screw in type in an adapter?
I was thinking about a Pacet but was concerned about the wiring?

Terry
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PostPost by: bill308 » Fri Sep 11, 2009 11:16 pm

Engine running temperature is an interesting topic. There are tradeoffs here.

A cooler running engine delivers more bhp and torque due to a more dense intake charge.

A hotter running engine delivers less bhp and torque due to a less dense intake charge.

Is it as simple as that?

No, there are tradeoffs. A hotter engine is more efficient (better milage), up to a point. Temperature swings are important from a reliability point of view. The smaller the swing, the better. If one could keep temperatures constant over the operating range, running clearances and tuning could be optimized for this temperature. It may not deliver the best torque and bhp, but engine life would love it.

If an engine has to operate over a large temperature range, all settings should be optimized (averaged) accordingly. If the engine could operate at one temperature, optimization is easier, even if performance suffers somewhat.

Overall heat rejection capacity is determined by the radiator capacity (including an oil radator). A Thermostat will only control temperature up to a radiator's capacity. A lower rated thermostat will open earlier giving more transient capacity. An engine thus equipped, will deliver more performance when the weather is cooler and during short trips.

Assuming a good radiator will limit temperatures to 110 C (2300F) under a worst case driving scenario, maybe stop and go traffic on a 43 C (110 F) day, then from a reliability/wearabilility standpoint it is desireable to run the engine a good bit under this limit. Tuning mixtures should be optimized for say a temperature of the highest available thermostat, if low wear is important.

From a reliability/wearability standpoint, the best case is to get the engine to temperature and keep it there.

Using a low temperature thermostat results in more performace but higher mechanical wear because the engine will likely be operating over an increased temperature range. The converse is also true, run the engine at a higher tempearture and you loose some performce but gain by reduced wear. As usual, there is no free lunch.

Do you want more life or more short term performance?

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PostPost by: CBUEB1771 » Sat Sep 12, 2009 2:10 am

bill308 wrote:Engine running temperature is an interesting topic. There are tradeoffs here.

A cooler running engine delivers more bhp and torque due to a more dense intake charge.

A hotter running engine delivers less bhp and torque due to a less dense intake charge.

Is it as simple as that?


Bill - There certainly are trade offs here and I don't know how to answer without becoming pedantic, boring and probably wrong. My following comments are general. I recognize that inlet charge and cylinder wall cooling are related but very different animals. We only cool engines with by auxiliary means (air/water/oil cooling) because we are still stuck with limitations on the performance of structural and lubricating materials. Remember Carnot Efficiency, we only want to cool the engine by conversion of heat energy into mechanical energy. We want that greatest possible difference between top and bottom cycle temperatures to maximize the performance of an engine. The water cooling jacket of an Otto cycle engine is a parasitic loss, although a necessary loss with current technology. The answer is to run the coolant as hot as you possibly can without causing knocking or premature lubricant failure. I remain excited about the future for the Otto cycle engine. With Porsche/Audi doing direct injection of gasoline and BMW doing linear, electric motor valve actuation we are poised to make advances that make electric vehicles look silly. Step in here M. Pelly!
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PostPost by: stuartgb100 » Sat Sep 12, 2009 7:10 am

Terry,

I decided on the in-line hose type in the end.
See attached photo.
If you've already got a switched electric fan, then your wiring is ready.

The Burton part number was REVEFC32.
Cost ?59.57 inc vat and delivery.

Regards,
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PostPost by: terryp » Sat Sep 12, 2009 7:16 am

Stuart
Can you specifically set the temperature on the switch or do you have to turn a screw up to a "known" temperature
My otter switch is wired as a switched earth , ie constant positive feed to the fan.
How is switch wired as I would imagine it needs powering?

Thanks a lot

Terry
PS I can't seem to find a 72 degree thermostat anywere, even with the QH number?
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PostPost by: paddy » Sat Sep 12, 2009 7:39 am

The switch doesn't need powering, it is literally just a switch.

It is advisable to use a relay for the fan, and not have the switch control the full fan current directly, especially if you have fitted a higher power fan than original.

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