Lotus Elan

Water Temp

PostPost by: Gasman » Thu Jun 19, 2008 9:02 pm

Following my MOT the guys said it was running a bit hot, this raised a number of questions:-

What is the ideal temp to run at? Does this still apply when using water wetter and how does this stuff work anyway? Is it worth using?
What pressure radiator cap should I be using?

Looking at the weather I guess all this will be irrelevant anyway, but it would be nice to get this set up properly

Thanks for any help

Mark
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PostPost by: gordonlund » Thu Jun 19, 2008 10:49 pm

90deg C /10 psi

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PostPost by: 1964 S1 » Fri Jun 20, 2008 3:32 am

Hello Mark,
I agree with Gordon and it can be a bit higher, mine run near 100 in traffic and fall back in open running. Decades of driving Elans have been similiar.
I'm not sure what water wetter is as I've never used it in forty years of Elan ownership.
How many MOT guys have owned an Elan? Do they know what they're looking at?
I'm so lucky that I don't have to go through what you Brits endure to keep Elans on the road.
If it runs and drives we accept that, (and enjoy Lotuses as they are...)
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PostPost by: rgh0 » Fri Jun 20, 2008 1:01 pm

Water wetter modifies the viscosity of water to increase its heat transfer coefficent. For the engineers in the group it effectively increases the Reynolds number. For non engineers this means that it is easier to transfer heat from inside the engine through the coolant to the air passing through the radiator and as a result the coolant runs at a lower temperature

The desirable temperature for running an engine depends on many factors. Theorectically the hotter you can run the cooling system the more thermodynamically efficent the engine and more power you can extract. This is why formula 1 engines run very high pressure coolant systems running at temperatures around 150C. They also and more importantly run at high temperatures because you can use smaller radiators and thus less drag.

In practice for a road engine however between 80 and 90 c is the norm to ensure the oil is in a reasonable operating temperature range, the heater works, and there is good headroom before the radiator boils at a normal radiator cap pressure level of 10 to 20 psi that the hoses and gaskets can easily handle. Clearances in a road engine and materials for things like head gaskets are selected based on this sort of normal operating temperature and pressure.

You could get more power out of a twink with a 150C operating temperature and also less drag because you could use the smaller radiator but you would have to totally re-engineer the engine to run at this temperature. For a start the head alloy would go soft running at this temp all the time so you would need to cast totally new heads in a new alloy just to demonstrate it is not a trivial exercise

An esoteric, anorak, engineering post but what the heck

cheers
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PostPost by: CBUEB1771 » Fri Jun 20, 2008 1:44 pm

rgh0 wrote:For the engineers in the group it effectively increases the Reynolds number.
An esoteric, anorak, engineering post but what the heck


Further meaning that the boundary layer in coolant, adjacent to the cylinder head and block internal surfaces, is thinned and the temperature gradient in the coolant is made steeper. Film coefficients, great stuff! No need for concern Rohan, you are among similarly afflicted.
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PostPost by: freddy22112211 » Fri Jun 20, 2008 4:27 pm

Many experts say 74?C. See old post below. My car seems faster when the engine is cooler. I used to run a 74?C thermostat, but run without a thermostat these days. Temperature is usually up around 90?C or so.
Gordon

Message 27047 of 27114
From: "Robert D. LaMoreaux"
Date: Tue Nov 4, 2003 11:20 pm
Subject: RE: [LotusElan.net] Next Cooling System Upgrade
> Keith, I do not understand why you have fitted a 87c thermostat? QED
> recommended a 74c thermostat and I am sure I remember comments
> regarding ~74c being the ideal temperature for a twin cam. Surely
> your engine is taking an age to get up to 87c because it naturally
> wants to be running cooler? Or am I missing something here?
>
> Regards, David (+2 with TTR 26R spec alloy radiator/swirl pot).

74C thermostat is probably about right for a normal twincam with the stock
radiator in summer months since there isn't enough cooling to prevent a 15C to 20C rise from the thermostat temp. With an oversized radiator capable of dissipating all of the heat generated by the engine, or in the cooler months an 87C thermostat would be about right.

Most modern cars have a 90C thermostat, but their radiator is designed so
that they can keep the car at 90C on a 50C day. Also most modern cars run at 90C to reduce emmissions, not to improve performance. There is a slight preformaance improvement at the lower temps for two reasons. One is the higher density of the incoming air if it is cooler, the other is the lower
likelyhood of knock.

If I had a radiator up to it, and in the winter months when my recored to 3
rows radiator is up to it, I like an 85C thermostat or as close to that as I
can get. In the summer months I have a 74C thermostat with a small bleed hole in it.

As for the 20 minutes to warm up, I suspect your thermostat is not closing
fully or you had the heater valve open. If the heater valve is closed and
the thermostat is closed fully the engine will warm up in a few minutes
since no coolant is being circulated, but if one of those is open it will
take much longer. When I had the thermostat with the bypass hole in it in
the car last fall and I drove on cool days it took a long time to warm up.
Changing to a thermostat without a bypass hole allowed it to warm up in a
matter of a few minutes.

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PostPost by: msd1107 » Fri Jun 20, 2008 7:17 pm

Rohan

Interesting comment about radiator size.

In theory, a properly ducted radiator should have a negative Cd. In other words, the heat extracted from the radiator is used to generate thrust - a real heat engine!

In reality, the improvement in thermal efficiency is very small. The absolute temperature difference is just too small to have any effect. The big improvement is the reduction in drag over an non-ducted system.

Of course, our Elans are not set up to take advantage of this effect.

The intake is too large, the airflow immediately turns turbulent without proper ducting, the radiator hardly gets any airflow, and the air exit is pretty obstructed.

And Rob and Gordon are correct about lower temperatures also. There is always a design effort to minimize heat transfer from the hotter areas of the cylinder head into the intake tract. Interestingly, the electronic controller for the Davies-Craig electric water pump allows the temperature to be set, so that it sould be set low for max power and high for better fuel economy.

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PostPost by: bcmc33 » Fri Jun 20, 2008 11:20 pm

The Reylolds Number could be described as the drag of fluid motion ? the lower the better. The best analogy I can think of is what we all understand by the drag coefficient of a car travelling at speed due to the resistance of air ? the lower the better.
I put Water Wetter in my car when I revised the cooling system with a full width radiator and the filler cap on the thermostat housing. I did this with the belief that Water Wetter is simply a wetting agent designed for vehicle engines to make the water ?wetter? by making it more ?slippery? by reducing the natural surface tension. My conclusion was that the ?slippery?, (or wetter water), would move more readily through the system to effect a more efficient cooling cycle.

What I should have done, of course, is to put the Water Wetter in before modifying the system to see if it really works.

Before modifying the system my car would run at 90deg C and the fan would always engage when stationary or in slow traffic.

We have not yet had any hot days this ?summer? so I cannot make a direct comparison, but on warm days the temperature has been 60deg C in normal running and 70deg C in traffic ? and the fan has yet to engage. And I have to say the engine seems to like it better this way.

I am running 82deg C thermostat and 92deg C temperature switch ? both of which I took as the best options from previous threads on this forum.
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PostPost by: bill308 » Sat Jun 21, 2008 12:23 am

You guys are giving me a headach with this tech talk and I should know this stuff as I do heat transfer for a living.

Rohan says Water Wetter changes the viscosity of the coolant and as a result, changes the Reynolds number. I bellive he is correct. So, high Reynolds number means more turbulant flow, which means higher convection, which means better heat transfer. OK. So, for a given ambient temperature, the radiator will run at about the same temperature, because we have not changed the total amount of heat to be rejected to ambient air and the air to radiator fin interface doesn't change. The coolant will run a little cooler because it is more efficient at transferring heat to the radiator. The engine will be cooler still, because it is more efficient at trasferring heat to the coolant. The end result is that the difference between the temperature of the engine and the ambient air is less and the engine runs cooler.

As far as a negitive Cd, isn't this nomencature for drag coeffieient? I don't believe a negative value is possible. I would suggest it violates the laws of thermodynamics. You don't get anything for free, entropy and all that good stuff.

A cooler intake charge means denser air which results in more torque and bhp. One can feel the difference by seat of the pants when running on a cold day verses a really hot day, so its not insignificant. A hotter engine means better efficiency by the law of thermodynamics. The trick is to run the engine hot, but keep the air/fuel charge cool. In large part this is what the twink setup does because there is low heat conductivity interface between the engine intake manifold and the carbs. This keeps the carb and fuel at a relatively low temperature and minimizes the heat transfered to the incoming fuel/air charge. Some heat of course is picked up during the flow through the intake manifold but I would guess this is minimal because of the short duration of charge exposere. A hot engine and dense fuel/air charge mean good output torque and power.

Further goodness from a hot engine is reduced losses due to lower oil viscosity and improved vaporization of the fuel/air mixture.

As far as engine heat is concerned, one would like to run at a farily hot, constant temperature, for efficiency sake, and get there quickly and remain there. This allows the engine to run at its optimum clearances. So, changing the thermostat for winter verses summer running may not be a good thing. One would want to run the engine at a steady state temperature at all times, for minimal wear and optimum clearance purposes.

OK, time for some more red wine, for medicinal purposes.

Bill
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PostPost by: msd1107 » Sat Jun 21, 2008 8:20 am

Bill,

No reason to worry about the violation of the laws of thermodynamics.

Thrust and drag are the same, but with the signs reversed.

Normally, drag is visualised as what happens when a body moves through a fluid.

Fluid moving through a tube also generated drag.

However, if energy is introduced to the fluid as it moves through the tube, it generates thrust, or negative drag.

A jet engine is a good example. Thrust is what is usually mentioned, but that is negative drag.

Those of us who have had the pleasure of perusing the NACA archives can see some of this.

But a car is not going to be able to generate significant thrust, since the energy rejected from the radiator is not significant enough to generate measurable thrust. Look at the energy rejected into the atmosphere from the engine compared to the energy generated by combusting fuel.

Anybody game to do the math?

David
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PostPost by: freddy22112211 » Sat Jun 21, 2008 8:46 am

At the risk of prolonging this topic even more, - for those of us with the small radiator that's not big enough - the best thing I ever did was fit a hand switch parallel to the temperature switch - which I always switch on when I slow down ie towns, traffic lights etc. Then the temp. stays at 90 all the time, and doesn't rise when slowing right down, before the temp. switch kicks in. Ideally a speed controlled switch would be best, - or - I've just had an idea - a sensor to measure the air speed in the air intake - have to think about that - should be easy!
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PostPost by: bcmc33 » Sat Jun 21, 2008 10:11 am

Isn?t it great how these threads develop ? it?s like conversations in the pub when you start with cars and two hours later end up talking about women.

However, Mark (Gasman) wanted to know if Water Wetter would help his cause in reducing the running temperature of his engine ? I say it would, but by how much?

Mark, try it without any other changes ? not the way I did it so that there is no way of knowing what affect Water Wetter really had on the temperature drop.

BTW, I did mention the significant reduction in running temperature to one of the well known ?usual suspects? from Leicestershire who simply said ?perfect for power?.

P.S. Just noticed the obvious error on the first line in my earlier contribution --- it should read: higher is better.
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PostPost by: SADLOTUS » Sat Jun 21, 2008 3:35 pm

Time for a guinea pig with a pancake on it's head methinks!
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PostPost by: SJ Lambert » Fri Nov 18, 2016 12:26 am

I've got the measurements of the radiator in the open wheeler and the slightly larger radiator in the sports racer somewhere - shall have to dig them out &/or re-measure the open wheeler's. It'll be interesting to see what temp it runs at. I've tested the dashboard gauge and it's accurate and have also tested two thermostats in the same pot and watched them open simultaneously.
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PostPost by: prezoom » Fri Nov 18, 2016 3:57 pm

Under my therapist's direction, my doctor, Dr. L. Otus prescribed a brisk outing.

Yesterday, Holywood3546 and I exercised our Elans with a run up my favorite hill. At the top, a bit over 5,000 feet, we stopped at an overlook for a brief respite, a look out to the Pacific, and among our conversations was, "How hot did your car get?" They were exercised with some vigor going up the hill. Bugs splats on the sides of the cars, minor Hooning, as they say.

Mine has a 190 degree thermostat, and as the water temperature hit that number, the thermostat would open and drop the temperature down to a little under 180 degrees. Then cycle back up to the operating temperature, only to drop back again. James used his electric fan, and his car stayed within his comfortable operating range.

Our discussion brought up modern cars and how the temperature stays stable under almost all operating conditions. So why does the Elan's system have these wild mood swings?
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