Coolant Temp Gauge

[type36lotus]

Here is my situation. Near the completion of the resto of my S3 Coupe' I ordered a new Smiths combo coolant temp/oil pressure gauge. This sat on my shelf for a 6 - 8 months. I finally install it and it reads about 40 F low. So I send it out to MoMa for checkout. It comes back, I install it again, same thing. I remove the gauge and immerse the bulb in boiling water, zips right up to about 215 F. Close enough for govt work. Install it back in the engin again, same thing. I do not have a heater (Florida) so the heater spot is taken by a 175 F thermoswitch for my electric fans. My digital meter shows the fans come on about 170 F. So there is coolant. Why does my coolant gauge not work? Steve Smith at Twincam Sportscars was also stumped. At this time I have an Autometer electric installed for coolant temp in place of the Smiths bulb and it works correctly. Any Ideas?

Apologies for long windedness,
Mike Geiger
66 S3 Coupe'

[khamai]

Mike,

Have purged the system of ALL the air??? You may air trapped and it is cavitating in the area of the temp gauge "bulb" causing it to "read" hot air.

Kiyoshi

[LotuSport]

Hi, Mike -

If you have an Autometer electric installed for coolant temp in place of the Smiths bulb and it works correctly, where are you taking the Smiths coolant reading from? ...Or is the Autometer electric just in place temporarily while you figure this out?

If the Smiths reads boiling water correctly on the stove, how confident are you that the Autometer electric really _is_ correct? And are you making certain that the Smiths bulb is reading only boiling water temp and not the bottom of the pan in contact with the heat source? That alone could account for a 40 deg F variation.

Best regards,
Bob
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[type36lotus]

The system is well purged of air, that was the first thing that Steve Smith checked (Steve is a well known in Florida (Sarasota) Lotus specialist. The Smiths Temp gauge is not hooked up. I have coiled the capillary tube and bulb up and stored it under the dash. I also had my digital meter's thermocouple attached. The meter, Autometer and fan thermostat all match with each other, give or take a few degrees. IE Autometer gauge pretty much matches the digital meter. The fans come on about when the digital meter and Autometer gauge show they should. Everything works correctly EXCEPT what has now become the world's most expensive mechanical oil pressure gauge!

Mike G.

[asc]

Mike Are you sure that the "bulb sensor" projects as far into the water jacket as the original one did.From my memory there were a few changes in that area of the gauge & possibly different fittings screwed into the cylinder head. Not projecting far enough into the coolant flow could give a false low reading. Tony

[type36lotus]

My car did not come with a gauge for the Elan. I ordered the one I have from Dave Bean, so having never seen a "REAL" one I would not know. Now as you have mentioned length. Performing a bench fit I was conecerned that the bulb barely extended past the end of the adaptor fitting. Then of course this fitting does not thread all the way in to the head. So that could be it. I would have expected the aluminum head to heat fairly rapidly and therefore have a slow gauge, but not a forever low gauge. It appears in my case that it never really gets there as I drove it around quite a while. What I may do is cut down the adapter so as to allow more of the buld to extend past.

Mike

[elansprint71]

Mike,
I have just been out to the garage to measure my bulb(!). It is just under one and a half inches long, so this may well be your problem as suggested.

Cheers,

Pete

[type36lotus]

Well the saga continues I have made a cut down adapter, it is as short as can physically be made and still allow the threaded parts to thread and not leak. The bulb sticks out quite far now, I am amazed at how far! But no change, still does not want to go over 145 deg F when mounted. I am going to bench test this bad boy once more. Then if it is reading OK on the bench I am going to introduce it to a persuader... my 12 ton hydraulic press, heh heh. Okay, not really. Any chance that the U mounting bracket could be distorting something and preventing movement? I did tap the gauge to see if it was stuck.

Thanx,
Mike G
66 coupe' with recalcitrant gauge

[asc]

Mike The u mounting bracket shouldnt be more than finger tight, I doubt its responsible. If your going to test the gauge, suggest leave it in the car release the sensor from the head, then the hot water treatment, at least that way you should proove the capiliary tube isnt kinked. My original sensor bulb (S2 elan) had hexagon headed adapter in cylinder head on to which a female nut fitted, the replacement unit had reduced diameter bulb and male nut. On initial assembly there was very little of the bulb in the water jacket. Result was I made a new cylinder head adapter out of 2 fittings brazed together and machined internally, that seemed to achieve a decent amount of the bulb into the waterflow and it worked ok, but that is until the tube fatigued and broke, but thats another saga. tony

[type36lotus]

Tony, funny you should mention fatiguing. As I was watching it vibrate about I thought to my self "How long will that last?? Anyway, the unit did pass the hot water test... again... as expected. Does anyone think it will make a difference which port on the cylinder head I install it in? I have no heater (hey it IS Florida) so I installed it in the rear hole. I wouldn?t expect it to make a difference, but...

Mike

[asc]

Mike The original UK build was heater valve to rear , temp sensor to front, worth a try moving it, it could be in a stagnant area. Also fatigue I did realise in the end that if you form a spiral of sensor tube coming straight off the head, this vibrating unsupported mass was most likely to be the cause of 2 factured tubes, hence all the experience with different level gauges & fittings! Latest one has 90 deg bend to rear and then the spiral of tube fairly well clipped up, this looks a lot better. Another comment -every one else I know is trying to get lower temp gauge readings- you got them for free. Tony

[type36lotus]

Free lower coolant temp not withstanding. I have moved the coolant temp bulb to the forward port, no luck, same situation. So I am going to give up, this thing just does not like this car or maybe any car for that matter! So as I have an electric gauge in lieu of the mechanical one, I am simply going to replace the combo gauge with a smiths classic 270 degree sweep mechanical oil pressure only. I will box up the combo for the next victim to spend endless hours on. I can order one from the people, which are restoring my fuel gauge.

Mike G
66 S3 coupe' with recalcitrant coolant temp gauge soon to be no more.

[type36lotus]

Heh heh, well the recalcitrant coolant gauge is no more As I previously stated it is now replaced with a Smiths Classic 270 degree sweep mechanical oil pressure gauge. While the dash (facia) looks different (no more combo), I like it better as all the instrument needles rest at the same angle. The folks at APT Instruments (www.gaugeguys.com) cleaned and calibrated my fuel gauge for $30 and supplied the oil gauge for $85 (tubing and fittins NOT included). From my door and back to my door in less than 2 weeks. Now I CAN say everything on the Elan works and works properly!

Mike Geiger
66 S3 Coupe'

[simonknee]

Now I CAN say everything on the Elan works and works properly!

Yeah right, look at the date!
Can't catch us out that easily