Lotus Elan

TC Running Temp

PostPost by: prezoom » Sat May 06, 2017 3:14 am

As long as the thermostat opens at the temperature as shown on the gauge and matches the rating, then closes when the temperature drops, it is working as designed. The multi bladed fan is on the water pump pulley, no switch required. The coolest it runs is when driving at speed including continuous running at 5,000 rpm. The radiator was re-cored to include another row of tubes after 40 plus years of faithful service, which is a questionable modification. Increased width would be more effective, thus the factory change from the Marsden to Spitfire style radiators. Agreed, blocking air from entering the engine compartment that does not pass through the radiator or is routed directly, and sealed, into the carburetors is of little use in keeping any engine cool. It also helps in the movement of air through the radiator by creating a low pressure area behind the radiator.

The temperature rating of the thermostat is a subject of great debate with regards to the twin cam engine. IMHO running an engine below 185 degrees, means increased wear, increased oil contamination, increased fuel consumption, increased emissions and loss of power among other things. In my last 4 cylinder racing engines, not tc, dyno testing proved that power increased above 204 degrees of water temperature, and 220 degrees of oil temperature. I am also an advocate of using a water to oil heat exchanger to stabilize both temps and speed warmup. Ford has a nice compact oil to water heat exchanger that fits between the oil pump and the oil filter that I am employing on my Plus2 Zetec conversion. With some minor changes in the water routing, it could be utilized on the twin cam.
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PostPost by: Sea Ranch » Sat May 06, 2017 6:18 am

prezoom wrote:. . . Agreed, blocking air from entering the engine compartment that does not pass through the radiator or is routed directly, and sealed, into the carburetors is of little use in keeping any engine cool. It also helps in the movement of air through the radiator by creating a low pressure area behind the radiator . . .


Sorry, Rob; not following here. Are you saying the foam over the rad is a good idea for cooling, or that it does not work?

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PostPost by: prezoom » Sat May 06, 2017 2:54 pm

Any form used to block the air from getting air past the radiator instead of going through it would be the goal. In my Zetec conversion, since I used an overkill radiator, I made the mounts, which spread across upper the inner fender wells and a piece of aluminum plate bolted to the top of the radiator. Fitted to the top of all this mishmash is a piece of a bulb style seal, similar to that used on sills and trunk/boot openings. The hood/bonnet will press agains the seal, blocking the passage of air. The sides of the radiator area likewise sealed against the inner fender wells. A 12" electric fan is mounted to the back of the radiator.
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PostPost by: Sea Ranch » Sat May 06, 2017 4:05 pm

Thanks, Rob. I know that's the purpose and theory of the foam block atop the rad.

You have to wonder about sealing off the engine bay, though. Lots of heat radiating from the engine into that bay . . . , no? Where does it adequately get pushed out from, and to? IE, from where does fresh/cool air come to push out the heat?
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PostPost by: prezoom » Sun May 07, 2017 3:08 pm

Haven't checked the Plus2 manual for any engine compartment mods yet, but on the Elan, the manual suggests cutting the holes in the inner fender wells to help extract heat. On mine, the PO did not cut the holes on the exhaust side, but placed one in each fender well. I think he had a better idea, and the fact that he works for Pratt Miller, who prepare and race the LeMans Corvettes lends some credence to his actions.

The area in the engine compartment of the Plus2 is much larger, though the basic area around and below the engine is about the same as the Elan. With the low pressure area created by blocking off what I call unused air, extraction of the heated are becomes easier. Another thing the Plus2 has, is a lip in the body where the upsweep joins the under side of the nose. Like a chin spoiler, it also creates a low pressure area, minor, but still more low pressure. To assist this area, I am placing an aluminum plate below the steering rack, the width of the opening to the engine area in front of the front crossmember/vacuum tank. This should also help the extraction of the heated air in the engine compartment, as it blocks off more air that can sneak past the radiator. If, I have an over heating problem here in the reclaimed desert, I may try adding a couple of inches to that lip to further increase the low pressure.
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PostPost by: prezoom » Sun May 07, 2017 3:13 pm

I should have a bit more clear on the plate below the steering rack. It will be fastened to the studs holding the rack, below the mounting plate, and the front edge will contact the upsweep.
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PostPost by: stugilmour » Sun May 07, 2017 11:37 pm

Bob, I may have missed something and coming to the topic late.

Your picture caption asks about using the thermostat housing bung as a port for a thermometer. That is how I checked mine.

I have a Clivey Boy housing with a cap, but the idea is the same. I used a baking or icing thermometer, readily available from a good grocery store for about $10. The temperature range is perfect to track coolant temperature from cold to operating temperature. Any coolant spillage is minimal, and just from thermal expansion of the coolant rather than it actually boiling. The icing thermometer is also perfect if you want to check things out at the stove top as Randy describes.

Would absolutely check the gauge is reading correctly, particularly in the critical 80 to 100 degree range, before I changed anything.

I found my gauge was reading 10 or 15 degrees C high. Solved the issue by soldering two Radio Shack paralleled resistors in series with the temp sender. Needed two resistors to get the correct value and to keep them cool.

I also have ceramic coated headers. Not sure if they were causing the issue, but happy with the fix.

Can you post the appropriate voltages or resistance to use for the two calibration dots? I can't recall if I have done that check on my gauge, and as the engine is being changed out (probably with a different sender) now would be a perfect time to check.


EDIT

Think you already posted them here:

lotus-electrical-f38/temp-sender-details-t32782.html

In the earlier thread you mentioned the sender may not be correct? In any case, for sure check with the icing thermometer before pulling the engine and what all.

HTH

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PostPost by: Quart Meg Miles » Tue May 09, 2017 10:17 pm

AHM wrote:With the old capillary type temperature gauge; if the bulb isn't in far enough it will read high. I replaced the fitting it screws on to for a nice new one which hadn't been chopped about and it read around 100c I put the old one back with its very short thread and it was fine.

You don't say why but I assume you mean because of radiation from the manifold.

I had an oil temperature gauge stuck through the sump plug for 30 years, but when, nine years ago, I moved it to its own socket on the exhaust side and deeper into the sump it read higher. Thinking it was due to the proximity of the exhaust (the original expansion box) I wrapped insulation and foil around the fitting to no effect. Now I have a 4-branch manifold, presumably hotter, and the readings haven't changed.

So the deeper the bulb the hotter the reading in my case.
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PostPost by: KevJ+2 » Wed May 10, 2017 8:56 am

I fitted this pot between the sender and gauge and used it to calibrate the gauge against readings from an IR thermometer and my electric fan dial switch.
The pot hangs behind the dash should I ever need to recalibrate.
http://www.ebay.co.uk/itm/5W-Wirewound- ... hash=item0
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PostPost by: Chancer » Wed May 10, 2017 10:55 am

I did that with the fuel sender on my 87 Westfield, it became non linear afterwards, I could trim it to give a true reading at full, empty or anywhere between, I think that I settled on a true reading for the last 2 gallons, it would stay on full for maybe 1/3 of the tank before descending faster than the fuel was really being consumed, TBF my Skoda is a bit like that.

Trim the guage to your correct/desired running temp and then just use it as a comparator.
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PostPost by: Sea Ranch » Wed May 10, 2017 4:10 pm

Nice idea, Kev and Chancer. :mrgreen: Must easier/faster than a fixed resistor. And the 5 watt wire-wound potentiometer should handle what's pushed through it. I will attempt to do the same :)

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PostPost by: Sea Ranch » Wed May 10, 2017 4:23 pm

For those interested in detail, an XJ-S owner has written up a pretty extensive overview of testing gauge and sensor separately and making adjustments with resistors:
http://www.efsowell.us/ed/jag/coolingsy ... eGauge.pdf

I must say I still hold to the idea that it is more efficient, simpler and the end result just as valid if you test/calibrate both gauge and sensor together, measured against a known thermometer, by simply removing sensor from it's port and placing it in a pot of water which is on a portable electric hotplate. Only minor difficulty is rigging up a litle platform for the hotplate in a location close enough so that the sensor and it's wiring will reach. Otherwise, everything else on the car can stay in place.

If the gauge/sensor combination needs adjustment, then the article above is a good guide to selecting appropriate resistance range needed. Then cut the sender's wire someplace convenient and solder in a potentiometer and start playing with values and needle position. :mrgreen:

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PostPost by: Chancer » Wed May 10, 2017 7:56 pm

You are right Andy, the advantage is that (at S.T.& P.) water will boil at exactly 100?c, infra red temp guns (I have a couple) are great as comparators but the indicated value will change according to the surface finish of the item, its not the best way to measure coolant temp.

I have a problem on my Skoda, the guage which was always rock steady at 90?c now sits at 80?c and sometimes goes up a bit, used a 330 ohm resistor and got the half scale deflection so guage OK, IR temp gun inconclusive, its either the sender (been replaced once for fast idle problem) or the stat sticking open a bit, tested stat in pan of boiling water, it opens fully but inconclusive regarding 80 or 90? so I will soon be putting the sender in a bioling kettle and will know for sure what to replace.
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PostPost by: gus » Thu May 11, 2017 12:27 pm

just for reference, my 47 year old temp gauge with a replaced temp sensor agrees within an immeasurable amount with a digital 4 wire platinum RTD in the top of the radiator.

A friend has an original smiths calibration box, and we may have calibrated it 20 or 30 years ago, I cannot recall.
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PostPost by: Bigbaldybloke » Sun May 21, 2017 11:13 pm

Several suggestions, first do as someone has suggested and remove the sensor and calibrate it against a known good thermometer or thermocouple, three points should be enough, cold tap water which is around 10 degrees, boiling water straight from a kettle which will be just under 100 degrees and somewhere midway should be fine to prove if the gauge is reading ok. The immersion depth should make minimal difference as long as it is around 10mm or more into the water. If the gauge is reading wrong which way is the error, if it's reading high that explains your problem, if it's correct the engine is running hot but not dangerously so, if the gauge is reading low you have a serious problem. Assuming the gauge is reading accurately what coolant are you using, water based with antifreeze, if so what % antifreeze, stronger will help, if proprietary non water based, that's as good as it gets. Do you have air locks, does the heater work well (mine was clogged up with what appeared to be balls of rusty coloured muck about the size of maltezers which I back flushed out). Check the radiator with an ir thermometer is all the radiator getting hot or only the top section, indicating the bottom part is blocked up reducing its cooling capacity. If this is clear, remove and check the thermostat, again in a pan of water gradually heated up with a thermometer to see when it opens, does it match the stated setting of the thermostat. If ok next check is the water pump flow, you should be able to see this through the radiator cap, remove it when cold and watch it warm up, you should see flow once the thermostat has opened, blip the throttle to increase the flow. Check the fans start and go the right way, this is a common mistake and easy to check! If all this is ok, it's serious and the head needs to come off to check its water ways and the waterways in the block. The block tends to block up more than the head - sediment sinks due to gravity. Hopefully this helps and you don't have to open up the engine.
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