Lotus Elan

Assessing sufficiency of radiator cooling fan

PostPost by: MrBonus » Tue Nov 06, 2018 4:03 pm

As my car was restored and upgraded roughly 20 years ago by two owners prior, I'm still figuring out what still works on it and what doesn't for a winter refresh.

I haven't driven the car enough in any sort of slow moving traffic but can anyone comment on the sufficiency of its existing cooling fan? Should I just give it a go as-is before trying to spend money upgrading this pinwheel?

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PostPost by: pharriso » Tue Nov 06, 2018 5:54 pm

You have the wide older radiator so you should have plenty of cooling capacity.

One of the keys to good cooling is to make sure that you have the recuperator bottle & that it has fluid in it so fluid can be sucked back into the radiator when the system cools down. I don't see any recuperator bottle in your picture...
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PostPost by: MrBonus » Tue Nov 06, 2018 7:19 pm

pharriso wrote:You have the wide older radiator so you should have plenty of cooling capacity.

One of the keys to good cooling is to make sure that you have the recuperator bottle & that it has fluid in it so fluid can be sucked back into the radiator when the system cools down. I don't see any recuperator bottle in your picture...


Yes, there is one mounted in front of the radiator! Thank you for your input. Since I'm planning on putting a good bit of money into wiring and brakes, possibly a CV joint conversion, I'd rather not get into substantial cooling upgrades as well at this time.
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PostPost by: mbell » Tue Nov 06, 2018 9:46 pm

Yup, the wide radiator should be fine, just make sure its and rest of the system are in good condition. Assuming it clean/good worse case would be swapping to one/two modern fans to help in stationary traffic.

I have this radiator on my car in Texas with couple of modern fans with no issues, fan kick in if idling or going slow for a while but have no issue keeping temp under control.
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PostPost by: 69S4 » Wed Nov 07, 2018 8:57 am

I used the Lotus fan on my (narrow rad) car up till a few years ago when I replaced it with a modern unit. The modern one is better but it's not a day and night difference. It's hard to quantify these things but, roughly, with an outside air temperature around 15C / 60F the Lotus fan would just about hold the temperature steady in traffic whereas the modern one will bring it down. When the outside air temp climbs the Lotus fan loses out but you'd have to be stuck in traffic for a long time before it became critical (2hrs is my worse day so far).

With the wide rad I'd seriously consider two smaller fans rather than one big one if you do decide to 'upgrade'. Most of the air seems to come off of the tip end of the blades so you get a circle of wind coming through the rad. Two small fans side by side would put a lot more air through than one big one.

In the photo you seem to have a strange rad cap that I've not seen before. For the recuperator system to work you need a cap with two vents - one to let the water out under pressure and one to allow it to be sucked back in. Does your cap have both those valves?
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PostPost by: rgh0 » Wed Nov 07, 2018 9:09 am

69S4 wrote:.......
In the photo you seem to have a strange rad cap that I've not seen before. For the recuperator system to work you need a cap with two vents - one to let the water out under pressure and one to allow it to be sucked back in. Does your cap have both those valves?



I have seen those style caps before and I think the red lever allows you to release the pressure safely to the vent pipe before opening the cap. Not sure if they come in a recuperation style where it can suck coolant back in from a catch bottle as the engine cools.

With regards cooling yes the standard narrow radiator and original Lotus fan can work OK in traffic in hot conditions if everything is in top condition. At least it did on my Plus 2 for many years. But there is not much room for any system deterioration especially in a hot climate or if you run into a traffic jam after a long hard run in hot weather. A wide S3 style radiator or aluminium replacement of similar dimensions and two modern ducted cooling fans covering most of the radiator face should be bullet proof

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PostPost by: MrBonus » Wed Nov 07, 2018 2:34 pm

69S4 wrote:I used the Lotus fan on my (narrow rad) car up till a few years ago when I replaced it with a modern unit. The modern one is better but it's not a day and night difference. It's hard to quantify these things but, roughly, with an outside air temperature around 15C / 60F the Lotus fan would just about hold the temperature steady in traffic whereas the modern one will bring it down. When the outside air temp climbs the Lotus fan loses out but you'd have to be stuck in traffic for a long time before it became critical (2hrs is my worse day so far).

With the wide rad I'd seriously consider two smaller fans rather than one big one if you do decide to 'upgrade'. Most of the air seems to come off of the tip end of the blades so you get a circle of wind coming through the rad. Two small fans side by side would put a lot more air through than one big one.

In the photo you seem to have a strange rad cap that I've not seen before. For the recuperator system to work you need a cap with two vents - one to let the water out under pressure and one to allow it to be sucked back in. Does your cap have both those valves?


I'll take a look at the cap when I get home. I imagine that's an easy, inexpensive "fix" if it doesn't allow the overflow bottle to function properly.

Since my car is basically a back roads toy, I am going to punt on the fan upgrade until next summer. If I notice rising temperatures, I will address it at that time.
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PostPost by: nmauduit » Wed Nov 07, 2018 7:02 pm

I think the output for the bottle is a radiator fixture (a tube getting out of the filling neck, above the bottom seating of the cap but below the top seating.
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PostPost by: mbell » Wed Nov 07, 2018 7:58 pm

The radiator cap looks like a standard US part shop replacement. Probably not an issue but i'd swap it out at a convenient time to ensure the car has a cap with the right vent functionality and pressure.
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PostPost by: derek uk » Thu Nov 08, 2018 12:04 pm

As said the cap shown has a flip lever to release the pressure a bit less dangerously than removing the whole cap when hot. With an expansion bottle system, which is recommended, the rad cap is just a blocking cap with no pressure release. This cap only removed for coolant changes. Removing it adds air to the rad which means rebleeding the system. Coolant then flows straight into the bottle which is kept about half full. Coolant expansion then occurs in the bottle. Up when hot and back down as it cools. Bottle cap then works like a standard pressure cap at perhaps 7 or 10 psi in this case.
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PostPost by: Bigbaldybloke » Sat Nov 10, 2018 11:10 pm

My plus 2 had that type of electric fan and I used it for about 10 years with no overheating problems in typical uk weather and traffic. When I came to rebuild the car after taking it of the road for years, the fan was seized and I opted for two smaller modern fans mounted on a custom built aluminium frame, the car is not back on the road yet so can’t say how they perform but they certainly seem to blast a good amount of air through the radiator. Also check the blanking plate is in place under the radiator to force air through it rather than bypassing it, similarly for sealing above the radiator which seems to involve sticking bits of foam to the bonnet.
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PostPost by: Apx » Sun Nov 11, 2018 9:24 am

If your reusing the old radiator, jet water through the radiator to clean out the insides ( and the rest of the engine). Jet water through the fins from the engine side to clean out the debris that gets trapped there, i was amazed at the amount of insects, leaf bits etc that came out. Also if you have access straighten any bent over fins to allow air free air flow. definitely as above comment make sure the sealing panel below the radiator is in place and doing its job. My S4 ran a standard radiator and single electric fan with no heating issues at all.
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PostPost by: JJDraper » Mon Nov 12, 2018 5:53 pm

Apx wrote:Jet water through the fins from the engine side to clean out the debris that gets trapped there, i was amazed at the amount of insects, leaf bits etc that came out.


I strongly advise caution when doing this with a high pressure washer. You will bend over the fins making the radiator even worse. Low pressure or a garden hose yes, but high pressure washer jet - NO. Been there done that..

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PostPost by: Apx » Mon Nov 12, 2018 8:10 pm

Good point above, my mistake in explaining poorly. I meant spray water in a narrow jet and yes i meant from a garden hose so it clears each gap. Thanks for the correction, i'm struggling to think of any job on a classic lotus that i would use a high pressure jet washer for. Neal
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