Ally radiator............

[Hamish Coutts]

Can't agree more Steve.

I had my narrow radiator re-cored last year with an uprated 3 row core. Still not sure if it's enough for heavy traffic in the height of a Scottish Summer (about 24degC!!)

Will be going for a wide rad when funds permit. I would advise anybody thinking about recoring or a new rad to go for the wide version instead.

Anybody want a nice, very low milage, re-cored rad?

Hamish.

[rgh0]

Hamish

A good 3 core small radiator works in my plus 2 at 42C in traffic in Australia on the road. On a 24C day the engine temperature sits on the thermostat 78 C setting and the electric fan never comes on.

In my Elan the same radiator handles 180 hp on the race track at 42C (just).

In a Scottish summer if yours does not work you have some other problem with your cooling system that you are trying to hide with a bigger radiator.

The orginal Lotus fans boith the engine mounted and electric were poor when new and worse now. A modern ducted electric fan is far superior, do you have one of these fitted ?

Rohan

[type26owner]

Rohan, sadly, you're wasting your time here...

[M100]

The narrow radiators are just not up to the job.

I've had no problems with the narrow one on my Sprint, It was re-cored like for like about 18 years ago and runs a standard 88 degC thermostat. The fan was uprated to a modern reversed blade one about 10 years ago as the original was getting a bit noisy. Apart from heavy stop start traffic, which I always try to avoid, the fan hardly ever cuts in during normal driving. I know the gauge is pretty accurate too as I ran with a thermocouple in the head tapping a few years ago when I had my temperature gauge rebuilt and once warmed up the temperature swing was about +/- 5 deg from 90, the fan cutting in at about 98. Coolant is 25% antifreeze.

[type26owner]

Hey Martin,
I also used a dual fan puller (reverse) flow setup. Mainly because the bonnet fouls the fans if they are on the upstream side. There's a little aero penalty to pay for doing it that way since the blades are flailing on hotter, less dense air.

You can nearly double the cooling capacity by adding a ducted shroud as Rohan says. Being stuck in traffic should not be stressful for that reason.

[worzel]

Hi all

If you're a cheapskate like me pick up a tatty early plus2 rad- they're cheap enough.

Add the cost of a modern recore and the whole lot only totals about ?120-130.

Pretty effective too!

John

[steveww]

OK after the last comments let me re-phase that:

The norrow radiator with the standard fan is just not up to the job.

Even so when my S4 had the standard norrow radiator fitted the engine temp appeared to be controlled by the cooling capacity of the rad rather than the thermostat value including when moving along at a reasonable pace. With the new much bigger rad the temp is controlled by the thermostat under the same conditions. I now know that some of the ducting for the norrow rad was not in place at the time, even so its cooling ability was still a bit marginal for me. Hey I am just reporting what worked for me, your mileage may vary

[type26owner]

Hey Steve,
Thermostats are not intended to control the highest temperature at all. They are there to make sure the engine does NOT run to cold only.

[wparslow]

What should be the normal operating temperature of a big valve twin cam, and what temperature should never be exceeded? Anyone know?

Thanks

Wayne

[type26owner]

Hey Wayne,
The temperature is limited by causing detonation or blowing the headgasket because the the aluminum head plastically failed from the CTE. Either is bad. I'd not exceed over 125C ever. The trick is just run it up high enough that the air being forced through the radiator can carry off enough heat. The higher the thermal gradient between the water and ambient air temperature, the better the cooling rate. Try it, this works. DON'T fear the heat.

I have the early slightly larger radiator and use a 90C thermostat. The 10psi cap provides a 115C boilover point. My fans come on at 100C and the worst overshoot of heatload causes the temp to soar up to 105C and then it will recover and bring it backdown to 90C again. That's a 10C safety margin to stay away from a boilover condition. Almost all cars are designed with a 10C margin.

You'll have to optomize for the temperature envelope that works best for the smaller radiator by going a little higher possibly is all. Maybe the same temperature envelope that I use would work fine and I would definitely try to use the 10psi cap first. Not only does it solve the overheating but it also makes the cockpit heater MUCH more efficient. I think intentionally Lotus did this to save weight and money on the cooling system. This design change to a smaller radiator was them being rather clever.

Having big temperature excursions that happen quickly are very bad for the headgasket. This is why you don't want too low a thermostat to prevent the headgasket from having the right clamping force from the headbolts. The higher expansion rate of the aluminum comes into play by preloading the headbolts enough for full combustion pressure not to blowout the damn gasket. The headgasket is the other iffy weak point of the twinkcam.

[stuartgb100]

Keith,

Would be interested on your thoughts for this planned setup:

The original (wider) rad, re-cored + an extra row.
No forced ducting.
74-78 degree Otter switch controlling a 9 inch fan, (pushing thru the rad).
10 psi rad cap.
72 degree thermostat.

This is based on Dave Vizard's recommended engine running temp of optimum 72 degrees......although I know your thoughts on the latter.

Would seem to me that the most crucial factor is to ensure no relatively sudden changes in temperature between the head/block interface. This is exacerbated in the Twinc due to the iron/aluminium (sorry... aluminum) components.

Regards,

Stuart.

[type26owner]

Stuart,
See the last posting above. All these things are compromises. There isn't anything cast in concrete but experience weighs in a lot. What works best is what does not break immediately. Headgaskets failures are a major pain for the racers.

Having a thicker core is not always better. There is airflow resistance to consider which can actually reduce the thermal efficiency. I had a bunch of data on this stuff back when I redid my cooling system. It's long gone now.

I have pictures of the fans and shroud if you're interested. It's funky but it works great.

[steveww]

The original (wider) rad, re-cored + an extra row.
No forced ducting.
74-78 degree Otter switch controlling a 9 inch fan, (pushing thru the rad).
10 psi rad cap.
72 degree thermostat.

This is very similar to my set up except mine is runing 82C otter switch and a 10" fan pulling. TTR also recommends a 72C thermostat for maximum power potential.

[M100]

I don't buy this low temperature running for maximum power argument at all. Virtually all modern road cars now run at 90-95 deg C (rather than historically 85-90 deg C) for emissions reasons, to reduce aerodynamic lossy grill openings and to ensure the heater functions well, but despite this change specific power over the years has increased, while specific fuel consumption has decreased (due to more precise control of fuel and ignition)

While I've not done any measurents on the Twin Cam I know from experience with the A Series in the Mini that despite spurious claims to the contrary it made little difference running at 70 deg C rather than 90 deg C, but running progressively lower speeds on the water pump (eventually moving to an electric water pump) and smaller radiators marginally increased power and reduced weight by a couple of kg. Even with the higher temperatures the engines lasted just as long between rebuilds.

While I've seen the circa 70 deg C = more power claims in numerous racing oriented texts, in all the technical texts regarding engine design that I've read I've not found one single reference to back up the low temperature coolant = increased power claims.

[type26owner]

While I've seen the circa 70 deg C = more power claims in numerous racing oriented texts, in all the technical texts regarding engine design that I've read I've not found one single reference to back up the low temperature coolant = increased power claims.

Neither could I find any evidence. They are just unsupported claims. It's rubbish.

Hey Mark,
It does not hurt you to install an ally radiator. They are more efficient in the heat exchange to the air. I can point out a car that does require an aluminum radiator which is a 62 Corvette. I've applied all the forementioned tweaks to the brass radiator and it is still lacking in capacity. The 30% better efficiency of the aluminum one will just tip the balance, barely.