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GT6 Radiator - Clean Sheet of Paper


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GT6 Radiator – If we had a clean sheet of paper

OK so my first attempt at starting a thread, so be gentle ! (GT6 Mk2 owner since 197

Have you noticed that Saloon and TR5/6 forum pages rarely discuss cooling issues.
The Vitesse and Spitfires get mentioned sometimes, with the easy fix for the Spitfire being the fitment of the wide radiator.
Whereas for the GT6 it is a recurring subject and there have been several different approaches to improving things, including re-coring/replacement, making the most of the existing system by cleaning and adding a header tank to deal with issues of aeration. Most cars that were raced in period or since seem to have tackled this in various ways, mainly seeming to end up with a larger wider radiator.

Basically it appears that Triumph did the best they could in 1966, with the technology available at the time and presumably the cost constraints of mass production. Given that the space in the front of the engine bay was taken up with the extra two cylinders, narrow and tall was the choice following the fashion of the early TRs, with the width being dictated by the chassis and the height by the line of the bonnet. The deep core and the extra top hose connection from the thermostat housing to the radiator filler neck suggests they were struggling from the word go. Enter the Mk2 with a bit more power and a front bumper raised to meet USA collision regulations, gave a second obstruction to the flow to add to that already provided by the chassis.

Space is clearly the main issue, but logic does suggest that as the grille opening is wide and shallow, the radiator should be also. The VW golf/Peugeot 205 conversions all use modern cross flow radiators but do require the radiator to be canted forwards.  The Honda Civic radiator is a down flow design of similar size to the original but probably a bit more efficient, albeit it doesn’t quite fit and some have tried it without obvious benefit. I have spent a few happy hours trawling the interweb for other options, but none seem any better than those already tried.

So the question is, ‘if’ we were starting from scratch, knowing what we know now, what should the approach be:-

1 – A wide version of a down flow design (similar to a Spitfire wide), omitting the filler neck to maximise the available height. This might look the most authentic and allow an almost normal use of the side valences. Could it be wide enough to compensate for the reduced height ?
2 – A shallow cross flow design to allow the radiator to be set vertically rather than canted forward (is this an advantage or disadvantage).  Bespoke design could provide top n/s and bottom o/s to match current plumbing.
3 - Retain engine driven fan (probably only OK with vertical radiator) or electric fan/s. Some say that our cast iron engines need a continuous waft of air and that waiting for the electric fan to kick in allows the heat to cycle too much.
4 – Construction in copper/brass or aluminium. (is aluminium better?)

A PDF of my thoughts on shapes for down flow and cross flow options is attached, with core area shown as a % of the original.
Something I’m keen to address on my car in advance of the summer and the RBRR as my existing radiator needs attention.

What do we think ?


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Can't be any help on your quest I'm afraid but it would be interesting to hear from anyone that ran a GT6 when new. Reason I ask is I've had a Mk2 for 5 years now and all I did when I first got it back on the road was to flush the standard radiator, fit new cowl and hoses, clear all the crud out of the waterways when I had the head off. The little bugger just doesn't overheat even during the height of summer during long ques into shows, driving in London or being stuck on the M25 !!!!!. I even tested the accuracy of the temp guage as I thought it was duff.

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Only thing I was ever told to do with GT6's is make sure the front scoop and side valances are in place.

Interestingly I was nosing at the 3 GT6's on the TSSC stand yesterday.

1 had standard fixed fan, 1 had the fixed fan and an electric fan, 1 had just an electric fan.

None had the front scoop fitted.

Had the electric fans been fitted as the car seemed to overheat??




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The standard radiator was perfectly adequate when the GT6 was new but I have a feeling that modern fuels burn hotter and more heat has to be dissipated making the standard radiator a bit marginal. However, there are a lot of GT6 owners running the standard set up who are perfectly happy with it. In fact last year my friend and I took our GT6s to France during the heat wave and running a standard radiator albeit with an electric and mechanical fan he had no problems with boiling or over heating.

When I restored my MK3 it was a budget restoration and I fitted a Golf radiator because it was £26.00 delivered compared with a whole lot more for a re-core. My friend Roy gave me a lot of help and the installation worked really well. I did manage to arrange things so that the radiator was only slightly tilted. Like Roy, I used standard GT6 hoses.

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Ive got standard rad, butt  its  well shrouded, like well shrouded
all roond, and underneath too.
ne engine fan either, just a 12 inch 13 blade electric fan infront of rad.

Butt, if air cant get oot frae inside the bonnet area, then it,ll get hooter
let air oot, moer come in, simples


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My car was 3 years old when I got it, & had the standard radiator.  It even had air conditioning from the dealership.  At some point, the cardboard shroud in front and at the top of the radiator was lost, but still the car had no overheating problems driving in the heat & great humidity along the coast of the Gulf of Mexico.  That included city traffic stopping & going up & down the mountain in Birmingham, Alabama.

All my overheating issues were the result of radiator sludge (send the radiator to be boiled out & painted), thermostats giving up, & head gasket failures.

I think there has often been trouble traced to people running the cars without thermostats.

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If you're having trouble with overheating in your Mk2 & are just haunted by evil spirits after trying almost everything, let me assure you that if you fabricate a fan shroud for your car, it will suck the heat out of the rad so hard you will wonder why you hadn't done it first.

I went almost forever with the worst overheating problem ever driving a Jaguar XK140 in coastal Alabama -  tiny grille opening, small honeycomb type radiator, big engine, etc -- and it was just monstrous.  Shrouding the rad to the grille doesn't do much.  An additional electric fan in front was almost no effect.  I researched & talked with lots of folks, & they kept coming back to telling me to just fabricate a fan shroud from aluminum.  I finally mocked it up in cardboard, cut it from aluminum cookie sheet, & BAM, problem solved.  

Notice that ALL modern cars have fan shrouds, & shrouds from the radiator to the grille are not very common.

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Thanks all for the feedback. All good stuff. I had certainly followed Roy's and John's Golf conversions with interest, but would like to keep the car looking original if at all possible.  
My Mk2 doesn't actually overheat, but the electric fan (a 12" Spal) doesn't bring the temp down quite as quick as I would like, or should I say runs for longer than I would like. In normal running, no problem at all and the fan generally kicks in when we stop and then runs on until the  temp drops as it should. I've wired the fan to run on with the ignition off and it just feels weird (and slightly embarrassing) walking away from the car when the fan is still running. I've put the sensor switch (an adjustable one) in the top of radiator quite close to inlet and this may be the problem as the sensor is probably seeing hot static water connected to the head, whilst the fan is merrily cooling the radiator core, with the cooled water not being able to go anywhere as it is not circulating. The core certainly feels quite cool when this is happening.  
The system is all pretty clean, but the radiator is good few years old and I would be tempted to put the original engine driven fan (8 square bladed yellow plastic jobbie) back on for a trial, if it didn't clash with two of the soldered on fan mount brackets.
I've got the front shroud and side valences fitted but the fan to radiator is not shrouded on the rear face. This might be something worth experimenting with as I agree a lot of 'moderns' seem to do this.
Will have a play as soon as I can get the car home from temporary (building induced) storage.
PS Did anyone have any thoughts (+ve or -ve) on the wide down flow radiator idea?
Ian F 😉

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An aluminium rad would (should) work much more efficiently - Ali tends to be used for all sorts of heat sinks etc...

Like quite a few have said, a lot is to do with how clean the rad and waterways are - Also suspect water flow is a key factor too...

When rebuilding my mk3, I looked for ages waiting for a sensibly priced aluminium one to appear - never did (in time) so fitted the new reproduction one, which had to have its neck shortened to clear bonnet. So, my current cooling is standard size rad, all new hoses (Si) plus elec fan only on temp sensor. Fan is same diameter as rad width. I also have fitted aluminium side valances and rad cowel. Oh, the fan is fitted on the engine side of rad - quite loud when running, but does draw through a lot of air.

Temp gauge typically sits to the left of half, but does creep to just over half if sat in traffic.

Not had any overheating issues (touch wood) and have driven a few hot days.

I don't have front bumper fitted, so probably get little extra airflow area with that...

In answer to the original question - I would go for same depth core in aluminium, but make it almost hexagonal in shape (not sure if shape matters so long as water flows through it) so keeping the same overall height also, but gaining quite a bit extra on the sides....prob close to 30% or so.

That would be quite costly to make though I suspect.

Anyone run one of those standard sized Aluminium rads on theirs..?

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Quoted from RedRooster
I am, but it's not over heating that is my problem more like vapour lock in traffic on hot days.

Oh & i also stood the coil off & made a heat shield for that.

This reminds me of my friend Jerry last year in France. It really was very hot and every time he stopped in traffic the engine stopped and wouldn't restart. This was fuel vaporisation. He had a plastic fuel filter just near the exhaust manifold. We got rid of that and things improved but the problem wasn't solved. He then cut up strips of his under carpet insulation and tie wrapped it around the metal fuel pipe from the carbs back to the pump. No more trouble. Problem solved.

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