Lotus Elan

Thermostat Problems

PostPost by: kevinrooney » Fri Mar 18, 2005 12:33 am

my temp gauge is indicating very high readings going into the 130deg zone . Suspecting a faulty thermostat I removed the gauge and the engine is running to cool without the thermostat. Having fitted two replacement thermostats with the same results I am slightly bamboozled The temerature rises steadily to 90 deg then continues up to 130, and drops back to around 98 . It will ocasionly climb again to 130, (presumably when the engine cools slightly and the thermostat closes again)..There is no evidence that the engine is running hot either by rough running or boiling rad. Has anyone else experienced this problem .
I also have a race prepared AH Sprite which runs without a thermostat but is fitted with a flow restrictor in place of the thermostat to ensure that the engine does not run to cold. Does anyone know if these are available for the twin cam engine ?
Many thanks for your help.
Kevin
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PostPost by: type26owner » Fri Mar 18, 2005 12:48 am

Don't know where in Lotusland you're located but if it's here in the USA then I got some news to relay. Stant has been having all sorts of quality control problems lately both with their regular thermostats and the SuperStat. They stick closed or once open they won't close again. I've given up using them entirely. Just fitted a RobertShaw Extra Performance 190F thermostat and have had none of that nonsense since.
<a href='http://www.cooperstandard.com/us/en/Aftermarket/Aftermarket_Products_Thermostat.asp' target='_blank'>http://www.cooperstandard.com/us/en/Afterm..._Thermostat.asp</a>
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PostPost by: john.p.clegg » Fri Mar 18, 2005 6:49 am

Have you noticed this fluctuation with your other guages (oil/fuel) if so replace your voltage stabiliser
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PostPost by: steveww » Fri Mar 18, 2005 12:08 pm

You can just cut the inner out of an old thermostat to make a flow restrictor.

BTW: I always drill a 3mm hole in the flange of the thermostat, I find this helps with air locks and temp stability.
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PostPost by: Hamish Coutts » Fri Mar 18, 2005 12:58 pm

Kevin,

130 deg sound hellish high. If your engine was running at that temp would nasty things not happen to it? Try putting the sender in boiling water to see what temp it gives Suspect there's more to it than a faulty thermostat or gauge though.

Let me know if you do the temp test.

I've had overheating problems recently and it turned out that my rad had the wrong core in it! (it was from a Triumph Herald 1200). Hopefully, the problem is solved now as I pick up my rad with an upgraded core, tomorrow. Will post details of results when I have them.

Think the point on the voltage regulator is valid and I'm going to try the 3mm hole in the flange - a fine idea. :D

Hamish.
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PostPost by: kevinrooney » Fri Mar 18, 2005 10:14 pm

thanks for all your help .
All other electrical gauges seem OK
Ill try drilling the 3mm hole in the thermostat. it may be an air lock problem and this may help. HOWEVER!! This is now the least of my problem I attended a track day for historic racers in MondelloPark In Dublin today . Had a bit of an ooopsie and ended with the front of the car buried in the bank. My shopping list now includes a front quater repair section, new front bumper,chrome grille surround. and a bucket of fibreglass resin.- Any advise on where to read up on fibreglass repairs and sourcing parts. New motto - never try to keep up with a proper race prepared lotus 7 in a stock elan+2. OUCH
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PostPost by: type26owner » Sat Mar 19, 2005 2:32 am

Most thermostats have a tiny indentation across the sealing surface which allows the air to bleed through. Just look closely and you'll see it. When I drilled the hole in thermostat I had overcooling problems here in California. The aluminuim head cools very efficiently in the airstream passing through the enginebay in cool weather like 10C and below. I'm now planning on putting a Fiberglass fabric shroud onto the bonnet with velcro which partially surrounds the head and reduces the convective cooling during the winter months.

Sorry to hear about about the off-roading excursion. No way can I stay up with my brother in his Super7 on the track. That's not a level playing field to begin with.
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PostPost by: fatboyoz » Mon Mar 21, 2005 3:56 am

Kevin,
Just a comment on why one fits a restrictor after removing the thermostat. I was always under the impression that the restrictor slowed the passage of water through the engine to allow time for the water to absorb heat and thus aid cooling. You state that it is fitted to reduce flow so that the engine is not cooled too much.
I'm confused.

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PostPost by: M100 » Tue Mar 22, 2005 8:38 am

130 deg C water is only possible if you have something around a 15lb radiator cap - the standard cap is 7lb (10lb +2) which would give you an absolute max water temperature of around 110-115 deg C

A lower (or indeed higher) pressure radiator cap isn't the cure though - your gauge is almost certainly reading incorrectly - there might not be a problem at all
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PostPost by: khamai » Tue Mar 22, 2005 5:58 pm

<!--QuoteBegin-fatboyoz+Mar 21 2005, 03:56 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (fatboyoz @ Mar 21 2005, 03:56 AM)</td></tr><tr><td id='QUOTE'><!--QuoteEBegin--> Kevin,
Just a comment on why one fits a restrictor after removing the thermostat. I was always under the impression that the restrictor slowed the passage of water through the engine to allow time for the water to absorb heat and thus aid cooling. You state that it is fitted to reduce flow so that the engine is not cooled too much.
I'm confused.

Colin. [/quote]
I'm not Kevin...

But, a restrictor is needed to as a way of balancing the heat transfer in both engine & radiator. Ideally it is equal, heat added to the coolant is eliminated by the radiator.

Without a restrictor the capacity of the radiator to eliminate heat would have to be PERFECTLY equal to the heat transferred by the engine.

If the radiator's capacity is greater then the coolant will remain too cold.

If the radiator's capacity is less then the coolant will not have ample time flowing through the radiator to cool. In such circumstances it is possible to overheat without a restrictor.

The job of a thermostat is to be a variable restrictor.
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PostPost by: rgh0 » Wed Mar 23, 2005 8:37 am

A bit of heat transfer and pump theory may help understand what happens in the engines cooling system.

When the temperature of the coolant system is steady the heat input in the engine exactly equals the heat output from the water in the radiator. otherwise the water temperature would either continually increase or decrease.

Increasing the circulation rate increases the rate of heat transfer. The "Reynolds" number is the determinant of heat transfer independent of the driving temperature difference and this increases with flow rate of water around the system. Slowing the flow decreases the heat transfer ability of the engine to the water and the water to air in the radiator.

However The main determinant of the rate of heat removal is the driving temperature difference between the engine and the water and the water and the air passing through the radiator. The thermostat is used to restrict the flow of water though the engine so it reaches around 80 to 90 degrees C at the engine outlet so that the engine runs at the right temperature. The radiator is then sized so that at maximum design air temperatures the heat added by the engine is removed by the radiator.

If at the actual air temperature present is less than the maximum design the radiator removes to much heat and the water temperature at the engine outlet drops. Then the thermostat closes to restrict flow. This lowers the temperature in the lower section of the radiator as the water is cooled to closer to air temperature sooner in its trip through the radiator. Thus limiting the radiators effectiveness until its heat removal balances the engines heat input and the engine outlet temperature is still around 80 to 90 degrees C..

Removing the thermostat creates 2 potential problems

1. To much flow can lead to cavitation at the suction of the pump, this damages the pump and can also stop the flow totally. The cavitation then stops and flow restarts and builds up until cavitation again causes the flow to stop. This surgin can damage the pump and the lack of flow can lead to engine overheating.

2. If the pump flows happily at maximum flow without cavitation you have maximum heat transfer removal available in the radiator at all times. This will normally result in to low an engine temperature unless ambient temperatures are very high or your radiator is undersized for the heat load. A restrictor can hold a reasonable constant temperature in a car used in limited circumsances such as track racing but not workable on a road car.

A lot of other variables and hard to explain properly without a lot of relatively complex equations and diagrams but the best I can do in laymans language.

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