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Rearadiator for a big V8 which one?


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Hi guys,

I'm getting massive problems trying to cool my V8 which is in a 86" 90 fronted hybrid which I use for challenges amongst other things, problems being I'm killing it with heat and not being able to cool it.

V8 90 radiator (kept clean after every event) 2x12" fiamm fans (supposed to be the dogs danglies) pulling from the rear with a cowl both run constantly when warm.

2nd brand new waterpump (just in case first one was carp) no airlocks, 14 degrees ignition advance, mallory electronic dizzy and coil kit, Mark Adams Tornado based chipped with C/O of 2.5 runs absolutely cracking dead crisp and sweet.

Its about 4.4 litre and only just rebuilt but has done a couple of hundred hours now, big torquey cam, gas flowed etc.

OK on the road for normal journeys, OK for playing and trialling,

But gets very hot when winching or getting proper stuck and pulling etc when temp goes up fans will not cool unless get out and about in fresh air for a drive.

Options move rad to back and use a big alloy rad on the back of truckcab with fans on, any ideas please boys?

Pro's and cons, know all about mud cannot get to the back and air cannot flow very well on the road (which is seldom), pipes underneath can get burst, winch can come back a bit into grill.

The bit that bugs me is how do i stop it airlocking and how will the water pump cope and is there an advantage of using a electric waterpump if so what happens to the original , what type of pipe and diameter is best, will it improve being an alloy rad and will it help in the back because of a bigger rad and further to pipe so more chance of cooling.

Last question which rad and fans to use?

Lots of questions but lots of problems and I feel sure I'm not the first with them.

Thanks for any help or advice, but it doing me bleedin box in.

Boothy :unsure:

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You say its OK on the road, if that includes plenty of loud pedal then the only thing missing when off road is airflow?

Two 12" fans will never match a decent 16" or 18". Before you rebuild the cooling system see if you can get hold of a Renault Espace fan, they actually come in pairs!

One minor problem is they are a push fan so need to be fitted in front of the rad but may be worth a try before getting the wallet out.

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Thanks Paul,

On the road it holds it own with temp but gets warm when sitting, about 90" with both fans running but once it gets hot its just very hard to cool it again, could'nt touch the bonnet a Tong yesterday, proper hot, and I've got 12 2"holes in the bonnet sides to aid a bit.

The only problem with front mounted is I spent ages moving the rad right back so i've got the 8274 motor behind the standard 90 grill which gives me a great approach angle but not much room (and then you wonder why you've got problems) but i will try a bloody big fan at the front perhaps even without a cowling.

Thanks Pete for the link its good, mind numming but good, but the question was never answered "did it work or not?"

Thanks guys

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know all about mud cannot get to the back and air cannot flow very well on the road (which is seldom), pipes underneath can get burst

get the airflow right on a rear rad install and it'll cool nicely, the fans are only needed when stationary, ally is going to shed heat a heap more efficiently than a stock rad, Summit racing do a good deal in ally rads :)

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Got an oil cooler? Fit one. It's surprising how much difference they can make. I bought one about a foot square at Sodbury for £3.

As has been said, a rear mounted rad should cool fine. I'd trawl the scrapyard for the biggest fan(s) you can make fit, and make sure they have a good seal on the rad. A big ali rad from a modern van, SUV, 4x4 or people carrier could be a good stop before calling Summit, although their ali rads are ludicrously cheap.

You say the engine runs sweet - is it running lean? Slightly lean will give good response & power but RV8's don't like being lean, if there's any way you can richen it up, give that a try. Replacing the ECU coolant sensor with a resistor to make it think it's a bit cooler than normal can richen the mixture a bit - 400 Ohms would make it think it's about 70C, 500 Ohms is about 62C, 700 is about 50C, 1k is about 40C. You could get sexercisey and use a 4K pot to get the full range of twiddle, with a switch to reconnect the original sensor when the novelty wears off.

Oh and don't listen to the diesel boys (if you can hear them over the rattling), you'd only spend all your time changing cambelts instead :P

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I would try to find out what flow your Fiamm fans have, I did a Google and on the Fiamm main website and they don't even admit to making fans.

Have a look at the flow figures for the Pacet Profans, particularly the hi profile. The 12" models have more flow than the Kenlowe and standard Pacet 16" fans. I have two 11.5" Profans and they shift a lot of air, but they do take up some room.

I would look at the fans again before relocating to the rear. I have put a rad in the rear using 38mm ali tube and silicone hose joiners. I was able to get the pipes high enough to avoid damage but it's not easy.

A couple of advantages of electric pumps are that you can bleed the system with the engine off, so you can hear what's going on. Secondly you can cool the engine when it's not running, leave the fans and water pump on and it will cool till it's cold if you want.

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A pair of fans from a V6 Mondeo shift a LOT of air, and the cowling is almost an exact fit for a 90 V8 rad....


Even off road with little/no airflow one fan keeps my 4.2 cool enough. Only once or twice has the second fan had to come on. This is with a standard V8 rad, an ally one would cool even better.

The advantages of rear mounting are, longer pipe run (assuming front engined) so more coolant and more pipe to lose heat through, possibility of bigger rad, doesn't get full of mud. But you need to ensure good air flow, roof scoop etc.

If you are finding the rad is getting seriously clogged with mud maybe rear mounting might be the way forward, if not then maybe you just need more efficient cooling at the front.

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How far back is your radiator? If you’ve got an 86” with the rad flat against the engine and a winch in front of it, it might be easy to pull the air through the grille (around the winch though) but you might be fighting a losing battle to push the air away afterwards down either side of the engine. Does it cool any better without the bonnet on? I’d suggest the rad and fans you have might be quite suitable, and moving it to the back will give space on both sides for air to enter and exit.

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Your description of the build indicates a few ponies …………. and ponies = heat………

To be honest a standard 90 V8 rad is barely up to the job even with a very mundane 3.5 …….. this rad is the same as the 2.5 NAD with a extra bleed pipe in the right tank ………..

A big problem with the standard rads is the core has small louvers on the fins to increase the surface area………… when these get filled with sh!t the rad efficiency drops dramatically, however, cleaning the rad rarely manages to get the sh!t out of the louvers………

I guess the best way forward is to increase the coolant capacity. I did this by having a rad rebuilt up from a donor 2.5TD rad as these were thicker……… the core in mine is a commercial ‘X’ core that has tougher fins (that can be power washed) and no louvers ………….the rad is a 4 core and the core pipes are massive …….. IIRC 13.5 x 3.5 mm. The only problem is that this is not a cheap option …………. Budget on the best part of £300.

In the quest to gain more capacity I also replaced thing likes the heater pipes etc with ¾ bore………………… the cooling system now holds just under 17 litres.

The thermostat is 88C and the rad switch brings the fans on in slow mode (series wired) at 93C (switching off again at about 89C) ………… if the temp rises to 97C then the fans then the second rad switch causes the fans to go to fast mode (fans in parallel) ………..

Even with the engine being thrashed on a rolling road the engine temp never went above 95C …………

Also with the V8 it is important to keep the oil at a sensible temperature and oil plays a very important part in the engine cooling ……………in front of the Rad I have a 19 row mocal cooler that is thermostatically controlled via the sandwich plate. The stat is set at 80C …………so less than 80C and the oil is not cooled ……….. important because cold oil is just as bad for your engine as is oil that is too hot. Mr Castrol told me to keep the oil temp ideally between 80 – 100C …………..



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Deviating slightly, what are the options for mounting an oil cooler? I'm planning on moving my rad to get it out of the carp, and I'll need a new oil cooler to replace the standard RR item that i took off. Putting it near where the rad would have been seems a bit pointless, as it'll get full of carp. I'm guessing the oil pump won't like pumping oil to the back and back again?

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Here goes,

I greatfully thank you for all your advice so far.

BBC, What I have for a radiator is probably exactly as described by you,

the fans are controlled by two independant temp switches mounted in an alloy housing in the top hose, one for each fan the predominant being the one on the power steering pump and alternator side (ie nearside) this switches on at 88" down to 68 before going back to open circuit,

Its mate does 94" (I cannot do degree's thingys) down to 76,

both these fans have an LED on the dash when a supply is sent to the motor, they also have an OFF switch LED which the switches a large flashing LED on to remind me to turn the things back on again arter getting out of water,

dead easy wiring, virtually foolproof operation, and works a treat,

therefore I know which fan is ON, which fan is OFF and which fan has been turned OFF, plus if switch is turned OFF and LED does not flash then there's possibly a supply fault (i.e. fuse gone), hope that makes sense, it does to me.

But all that theory and wiring is carp if they don't cool it,

No i've not got an oil cooler for the sump and yes I know I should have, I will try to squeeze one in.

I spent a lot of time concerntrating on getting the 8274 motor right back behind the standard 90 grill, which resulted in hardly and space behind rad to water pump (which has had its shaft shortened at the end) and about 5mm between the winch motor and the front of the rad.

The two Pacet fans (I put down Fiamm earlier I'm sorry to Steve Hiatt) are very thin but apparantly have a very high output.

My temprature gauge is a Racetech capillery type, same as the oil pressure gauge.

The temprature it indicates agrees which the onset of the fans which is good and will work underwater, being mechanical is in my eyes infinitley more reliable for the circumstances the vehicle tends to find itself in (sounds posh that but it was a nice way of saying in the sh*t).

I think if I had a bigger rad or an alloy rad at the front now, I would struggle to fit in in around the winch etc and maybe the option is to rear mount it behind the truckcab (on the cage) hopefully in alloy with two Mondeo or Freight Rover fans in a proper cowl, the extra pipe work will vastly improve the capacity also, and stop it from getting clogged with god knows what,

mount behind the grill a big oil cooler using the one of the Facet fans to chill it, also increase the size of the autobox cooler at the same time (now having more room), and not be overly concerned if on the day it does get muddy at the front.

I could also sqeeze under the cage a deflector to push a bit of air down to the radiator whilst on the move.

Just the problem of will the water pump send it to the back and will 2" steam pipe or 2" hydraulic pipe do the job?

Fridge Freezer,

how do I put this,

the diesel boys get an stirring in their jockeys when the V8 blasts up a bank or a mud run (so do I), and never will I give up and go to diesel,

a good diesel reminds sounds like the dishwasher on an intensive wash (a constant clatter clatter clatter), no instant roar of life.

Keep the V8's burning, but not quite so hot!!!

Boothy, now deeper in thought. :unsure::unsure::unsure:

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Having moved a rad to the back to solve the same problem a few years ago I wouldn't suggest it as the first option. (just routing the pipework in itself was hard enough) The fact that the engine does cool down when driving along shows the problem is air flow rather than cooling fluid capacity. You obviously can move the rad but you shouldn't need to.

Have you thought about doing some air flow analysis to see how the hot air flows? I did this using a combination of smoke matches and a little flag on the end of a stick and then comparing with my car. After messing up the bonnet I worked out that improving the airflow where it was already flowing fast was the answer, chopping the inner wings around the exhaust manifolds made a big difference.

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Thanks again guys for all the advice,

After much time trawling scrapyards and the likes Pugwash comes up with an absolute barnstormer of a rad from Summit in the good old USA, which I've just ordered.

Now the thought behind this idea is to stick it in the back (after all) it can and should fit the front if not suitable at the back, if that fails it can always be sold or passed on to the Rangy boys (get the idea).

So going to pipe it to the back in 40mm Hydraulic pipe when it arrives, try the 2 Pacet fans at the back, lump a big engine oil cooler on the front, fan in the bonnet facing up, 2x100 amp alternators, Bobs yer Aunt Fanny = 30 bhp down.

But (here's the clever stuff,we think) the engine gets hot, the rad cools it, the hot air from the rad is now blown from the rad back to the engine, this makes engine hotter, which in turn makes rad hotter , which in turn makes engine hotter, and so on, (we think)

Now if we pipe hot water to back of vehicle and blow into fresh air this should make engine cool, and no crud laying on cores from swamp or mudbath should help the issue, plus winch bitch pratting around at back of vehicle with waffle boards etc will get addititional blast of hot air (this time not from driver, but from engine heat) should get a move on before he overheats, begins to sound good doesn't it?

Thats the thinking, I will post some photo's and let you know the results hopefully soon.

Boothy :D

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I play with Hillman imps quite a bit and we have lots of issues with radiators and mounting them at the wrong end! :D One trick that has been done is to run with 2 radiators. Either one auxillary rad to give a bit of extra cooling or use one small one in the normal position as a large header tank. Heater matrix's make good auxillary rads and are normally fairly easy to fit in. As has already been said oil coolers make a big difference, just make sure that there is some flow past it! :rolleyes: (common mistake on imps!!) One option that was done on one of the race cars was to mount the radiator horizontal with ducting to give a good air flow in. This meant that it could stay cool on the start line without the need for a fan. Good ducting for any position of radiator can make a huge difference. Although on the landies there isn't that much room and you don't want to end up with just a big container for mud! :D



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