Lotus Elan

Engine Mean Temperature

PostPost by: type26owner » Wed Feb 04, 2004 1:20 pm

Readjusting the mean temperature range of my engine from 70C up to 95C seems to have changed the operating temperature of my Webers too. They now tend to be cool to the touch if the car is not stationary for long periods. Use to run so warm I could only touch them for few seconds before it was uncomfortable. I can formulate a theory as to why this might be true but I have no way to actually test it other then to change out the thermostat for a 70C and reverse it. I've not done this so maybe it's just my imagination gone wild. Anyone else notice this effect before?
Keith
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1704
Joined: 18 Sep 2003

PostPost by: elansprint71 » Wed Feb 04, 2004 2:39 pm

No.
User avatar
elansprint71
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 4438
Joined: 16 Sep 2003
Location: Cheshire, UK.

PostPost by: type26owner » Wed Feb 04, 2004 4:08 pm

I've solved my overcooling issues. My thanks to the person that suggested it was the thermostat because that was absolutely correct. Turns out to be quite interesting to learn about how a thermostat works. Particularly the low flow performance of the different types that are available. Learned all of them have a small indentation across the sealing surface which allows any trapped air to escape but it's very tiny. Thermostats have no affect on overheating issues unless it's failed. They are all designed to fail open though.

Tested the 195F Robert Shaw 'balanced' type thermostat. It worked but has huge hysteresis at the opening temperature. On intial warmup it would go to 100C and then inhale a cold slug of water and rapidly cool the engine to 80C within about a second. Not so good. It would then continuously cycle the temperature between 90 and 100C on a period of about one minute. A bleed hole might help stop this and make it a good choice. It's got lots of opening area and not affected by a water pressure differential impeding the opening of the valve. My son should use this one in his 383.

Have installed and going to use from now on a 195F Stant Superstat. It has some mechanism I don't understand yet which catches the plugger from moving intially when the wax actuator starts to melt thus delaying and dampening the low flow problem. It would cycle too just like the Robert Shaw just at a longer period.

Decided what was needed was a bleed hole. Creating one has totally dampened away the oscillating behavior of the Superstat. It has lengthened the warmup time by about 50% but the calmed down the temperature excursions about the mean so changes happen much more slowly. A .12" hole is just about ideal if you allow it to warmup. However if I were to immediately to goto a steady cruise speed of 60mph with a stone cold engine it will only warm to 70C when the ambient is 10C or below. Only question now for me is whether this configuration is going to behave well with my present electric fans temperature regulating setup and the ambient goes up. Worst case is when the really warm weather comes back I'll have to change the thermostat to the next colder one so that the operating ranges don't overlap like they do now. I don't have an overcooling problem when it's summer here. B)

I only was able to diagnose it was a thermostat problem by covering the entire frontal area of the radiator including the top and bottom tanks from the airflow coming through the front grill. Also had to get the heater water valve to completely close using the inadequate stock wire cable (added a spring).
Keith
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1704
Joined: 18 Sep 2003

PostPost by: JACKJABBA » Wed Feb 04, 2004 5:12 pm

Keith,
How lond does it take your engine to warm up to the operating temp of your thermostat, if the car is left to idle from cold? Just interested in the warm up period of other owners cars, as mine can take over 10 minutes, which makes me think it may need changing.

Regards Jack
JACKJABBA
Second Gear
Second Gear
 
Posts: 84
Joined: 17 Sep 2003
Location: Middleton St George, Co. Durham

PostPost by: steveww » Wed Feb 04, 2004 5:18 pm

Must admit that I have never heard of over cooling before but then again my S4 only goes out in the summer. I have always drilled a small (3mm) hole in the thermostat flange to help with the air lock problems you get on the elan. I also find like you have that it makes the temp more stable, if at the exspense of a slightly longer warm up period. I always let the car warm up first before driving off - mainly because my wife will have forgotten something and has to go back in to the house to pick it up :P
User avatar
steveww
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1824
Joined: 18 Sep 2003
Location: Northamptonshire, England

PostPost by: type26owner » Wed Feb 04, 2004 8:35 pm

Jack,
I've not measured the time it takes to warmup from idling alone. Can speculate it takes pretty much the same amount of time for all of our twincams to warmup though. Might be a bit quicker if the engine is running very lean. Little slower if you've still got a fan mounted on the water pump. A failed thermostat would lengthen the time too. If it's sitting stationary with no mechanical fan flailing at the air then I suspect the ambient temperature has very little influence on the time it takes to complete this thermal process. It's mostly due to the amount of thermal mass. Being truthful this is my everyday car so I never just sit there stationary and let it warmup. <_<
Regards,
Keith
Oh, forgot this point. Having the heater water circulating and the heater fan going will have the biggest impact lengthening the time though.
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1704
Joined: 18 Sep 2003

PostPost by: type26owner » Thu Feb 05, 2004 2:23 am

Okay I've saved the best news for last. Elevating the engine temperature has transformed the wimpy heater into like a blast furnace. I was forced to get the heater water valve working for the very first time (been about seven years). Now my warm toasty comfort range is achieved at just half throttle. :D
Keith
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1704
Joined: 18 Sep 2003

PostPost by: gobw2 » Fri Feb 06, 2004 1:52 am

Yeah, Kieth - glad to learn we are on the same page again.
I was going to tell you about my wife's Ford - they all - GM too - have aluminum engines and plastic intake manifolds now. Her manifold went & as it has cooling passages, they had to drain to replace. Rather than put the old stuff back in, I told dealer to flush and put in a new thermostat (my nickel), so I would not have to mess with it for 2 years. Well, the new thermostat is not like the factory original. when it is cold ( below 10 degrees), it gets to operating temperature and holds where it always did at part throttle. but if you step on the gas, the temp drops to cold, then goes a little warmer than normal and slowly back to it's usual spot - every time. My diagnosis - weaker spring on new stat - pressure of waterpump at higher revs forces valve open more than it should, slugging engine with cold water. Cold water cools pellet & it applies greater force.

i suspect Temperature swings like this greatly shorten engine life. Going thermostat hunting when it warms up. George :wacko:
gobw2
Fourth Gear
Fourth Gear
 
Posts: 975
Joined: 25 Sep 2003

PostPost by: type26owner » Fri Feb 06, 2004 3:52 am

Hi George,
You're description exactly fits the scenario where the water pump is forcing the thermostat valve open with excess pressure. The Robert Shaw brand is not the standard planar poppet valve design but instead is a cylindrical design which supposely is not affected by a pressure differential across it. This could just be sales hype but worthwhile checking out.

My engineering style after having thirty-five years practice is to do intensive reference research first on any new subject. I then apply it through thought games by going off in many tangents until I can predict with reasonable certainty what will happen before it really does. Sharing this process with others is called mentoring. So when you mention we're on the same page. I've just taken the time to read and fully understand all the possible pages. It just took me awhile. :)

That said, by my calculations I only need 1:70 (3mm versus 25mm dia) of the total flow the thermostat is capable of providing to maintain 90C when the ambient is between 10 to 0C and when the car is in motion. If it got to -10C ambient, the engine would overcool by wind chilling alone with no water flow through the radiator. Luckily for me it does not get that cold here. I've already gotten spoiled by having a warm cozy cockpit now within five miles. :D
Regards,
Keith (Stunt Driver Bill Hickman fan!)
p.s. Having the Webers operate at slightly below ambient temperature was a total surprise. That wonderful change I didn't foresee.
type26owner
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1704
Joined: 18 Sep 2003

Total Online:

Users browsing this forum: No registered users and 13 guests