Lotus Elan and Lotus Elan Plus 2 Forums

My car has the big ol? BDP. So it?s an odd one.

It has a big custom radiator that sits above the rack and is almost full width with a 2.5? (about) gap on the right side. It also didn?t have anything closing the gap under the radiator.

I installed two 9? fans for around town cooling and they work great keeping it under 190f.

On the my first highway trip (90f ambient) it crept up to 210f at which point I slowed down and put on the heater. This seemed to satisfy it and the temps dropped to 195ish.

I wanted to fix the highway overheating issue so I made some aluminum panels to close the gaps below and on the sides of the radiator. It already has a foam piece on the under side of the hood.

I haven?t had a chance to test it other than a quick drive around the neighborhood.

The hood seems to get pretty hot.

My question is, has anyone sealed the gaps around the radiator enough to cause the engine compartment/ hood to get too hot due to all the air passing through the radiator.

Kyle

BDP? What is that? A Ford engine from the 1930s or the 2018s?

Have you cleared out all the crud in the cooling system with one of the proprietary... crud-clearers?

Radiator was removed and boiled out by a radiator shop about 8 weeks ago.

Here's a pic that shows the radiator and one of the new panels on the right.



Before the panel showing the gap on the right.

Go back to your racing days. Any air that enters the nose, should either go through the radiator or the trunking to the carbs, no place else. Do you have the factory recommended holes in the inner fender panels? My S2 has one on each side. This allows hot air to exit into the fender wells. The car still has the original radiator and it is on the marginal side. The multi bladed plastic fan is engine driven.

When I did the 2L Zetec conversion on the Plus2, I bought a DYI aluminum radiator from wizzardcooling.com. On the tall side, 19" and 22" wide, so I had to slip the bottom down inside the nose. At the top of the radiator, I made a flange that goes fender to fender and fits up against the hood with a strip of bulb weather seal that does the actual sealing against the hood. Flanges fit up against the two side tanks on the radiator, more bulb seal. All incoming air is blocked from by passing the radiator. We get 100F/38C days here and the engine temps never get over 190, except in stop and go traffic where they go up to 195. One 12" thermostatically controlled puller fan. The engine has the standard Ford 192F dual phase thermostat. No extra holes in the inner fenders on the Plus2, don't need them.

Thanks Rob.

For a pure racing car, no argument. 100%

In this case, I'm wondering about excessive under hood temps when in around town traffic. But I guess that at around town speeds, air through the nose is minimal, so the gap filling panels likely make little or no difference.

This car does have the vents in the upper side engine compartment panels. They're actually quite large. They were there when I got it. They seem like a good idea. I was even thinking of added a small (~4") fan to the exhaust side vent (in the fender well) to try to move some hot air out of the engine compartment when in traffic.

I may be over thinking this. lol.

-Kyle

Kyle,

I don't see how letting more (relatively) cooler air pass through the radiator into the engine compartment would heat up the hood. The heat is coming from the engine, not the incoming air.

How hot is the hood getting? You can get an IR thermometer for about $20 and test it.

In any event, if the hood is "too hot", the solution is more air passing through the radiator, and out of the engine compartment, not less. Bigger/better fan, vents in the fender wells, better sealing around the radiator, etc..

I'm thinking that you should focus on engine heat, not hood heat. As long as the paint isn't blistering...

Steve

[quote="disquek"
In this case, I'm wondering about excessive under hood temps when in around town traffic. But I guess that at around town speeds, air through the nose is minimal, so the gap filling panels likely make little or no difference.

This car does have the vents in the upper side engine compartment panels. They're actually quite large. They were there when I got it. They seem like a good idea. I was even thinking of added a small (~4") fan to the exhaust side vent (in the fender well) to try to move some hot air out of the engine compartment when in traffic.
[/quote]
I've done a similar gap filling on my street S4, following a heating episode after a track session : fiberglass cowlings around the rad, foam all around closing the gaps including bonnet. The carbs get fresh air from the front.

I can see that the bonnet gets hotter, since it does not get much cool air directly from the gaps - but the radiator has improved in efficiency, as now all the cool air that the nose swallos has to go through for the coolant, and none is wasted pushing the remaining hot air under the bonnet. Electrical fans are enough to cool the engine even in summer traffic jams.

If the fear of damaging the paint is becoming an issue, an additionnal fan would help moving hot air, but I would not just pull through the side opening as the efficiency of catching hot air above the head won't be that great because of the distance and alternative paths of least resistance (unless you cowl the head/outlet fan path... rather extreme), I would rather try to push it away - which is to some extent what the rad fans are doing, if with air that has been warmed up. Maybe as suggested measuring actual bonnet temp would help decide if something needs to be done other than adding a manual rad fan switch?

Good points.

My thought about hood temp was that it would be a function of heat directly from the motor plus heat from the air that had passed through the radiator.

In a race car where there is a ton of air moving through the radiator at speed the delta t of that air is very small (a few degrees). But I?m thinking in a street car in traffic where almost all air movement is from electric fans, the delta t of the air going through the radiator is far higher.

So I was thinking that letting in some cooler ambient temp air would help. But this would be a compromise as it would hurt at highway speeds.

I have IR temperature guns and pyrometers. I will measure the hood temp. That?s a good idea. But I have no idea how hot is too hot. I?ve measured the motor directly (cam cover). It was 210f ish. Which matches several modern cars where I?ve done the same. So likely the hood is in that range.

I?d thought that the Elan capturing heat under the hood was something of an known issue.

It would be interesting to put some yarn pieces in various places and see if things are working as expected. Specifically the vents to the fender wells.

Also, the fan I was considering for the fender well vents would be pulling air out of the engine compartment and into the fender well.

Kyle

disquek wrote:I have IR temperature guns and pyrometers. I will measure the hood temp. That?s a good idea. But I have no idea how hot is too hot. I?ve measured the motor directly (cam cover). It was 210f ish. Which matches several modern cars where I?ve done the same. So likely the hood is in that range.

I would start being worried above 60?C (140f), and definitely at 80?C (152f) when I think fiberglass may start to deform (esp. if under strain). Also paint discoloration over time may occur at high temperature, depending on the paint, so if you have a hot spot it will show more than a hot area...

disquek wrote:It would be interesting to put some yarn pieces in various places and see if things are working as expected. Specifically the vents to the fender wells.

Also, the fan I was considering for the fender well vents would be pulling air out of the engine compartment and into the fender well.

you'll have to stick cameras under the bonnet or near the wheels to check the yarns... in any case I would wonder if a small fan at the side would not just pull nearby air from the bottom as much as hot air heated by the cam cover, you may try in the open how far your small fan can pull before attaching it to the body...

disquek wrote:I?d thought that the Elan capturing heat under the hood was something of an known issue.

it is, but that changes with actual engine (yours is more powerful, hence uses more heat when running, then how much of that heat actually stays, convected or otherwise, remains to be checked)...

As a first step I still would try a minimal approach which would be a manual switch to force the 2 fans on so that a massive amount of air is pushed into the engine bay, certainly a lot more than what the side fan would suck. This would stir the hot air bubble forming above the engine, even if it is air warmed through the radiator, it would be a lot cooler than the hot air bubble.

Also, the exhaust is usually an important source of radiation inside the engine bay : you may want to wrap your header as a first step to investigate that lead.

disquek wrote:
My thought about hood temp was that it would be a function of heat directly from the motor plus heat from the air that had passed through the radiator.

But the source of the heat (the engine) is the same. The radiator isn't adding any on it's own. So if there isn't any "heat from the air that had passed through the radiator" then that heat would still be in the engine, or radiating from the engine to the engine compartment. Resulting in either a cooked engine, or the same heat in the compartment, or somewhere in between.

nmauduit, Great stuff! Thank you! The header is ceramic coated. My thought was to put cameras to watch the yard. I have a great cheap bluetooth endoscope that should work for this.

Steve, good point. The heat is staying under the hood regardless.

It's worth mentioning that the car has had this motor and paint for a looooong time. So it's likely that it'll be fine.

I'm just trying to be very careful and to improve it where I can.

Thanks for the help!

-Kyle

Some people drive with the bonnet (hood) slightly open, others install a vent in the bonnet (hood). I have an Australian friend, it's hot where he comes from, who had these cars when they were new, and never had an overheating problem. I am inclined to think that the problem is limescale inside the water jacket. My engine was badly scaled when I overhauled it.

Richard Hawkins