There’s nothing worse than having a car that overheats. That terrible
fascination that develops with the exact position of the needle on the coolant
temp gauge as you watch its inexorable movement upwards. Is the needle this side or that side of the ‘M’? Surely it’ll go downwards when I
descend this hill... Oh well, it’s now only at two-thirds, er, three-quarters, er,
four-fifths.
Bugger!
A car that overheats at speed – for example, when climbing hills – has
inadequate radiator and/or water pump capacity. We’ve previously covered in
detail how to go about testing your water pump (see Water Pump Testing)
but what if the problem is the radiator? It’s possible to spend hundreds of
dollars improving the radiator – but how do you do it at half the price? The
answer is to use a secondhand radiator from another, more powerful, car...
The Car
The overheating problem developed on my 1988 2-litre Maxima V6 Turbo.
Initially I noticed that it was starting to run warm in normal urban conditions
– and got hot when climbing the steep country road hills around where I live. I
took the radiator along to a repair place with a vague idea of sourcing a new,
larger core or having the original one cleaned out. However, when I saw the
costs being quoted for new cores (and also even good condition used radiators) I
abandoned the upgrade idea and settled for having my existing rad disassembled
and cleaned. This cost a little under AUD$100.
For a further six months, all was well – then I noticed the same pattern of
increasing temps as before. Either the radiator was again blocked (which seemed
unlikely), the radiator fins were starting to corrode away (which reduces
radiator efficiency very quickly), or the radiator was now getting too small for
the power that the more highly modified engine was now putting out. Or, perhaps
a bit of all three...
This time I decided to replace the radiator with another unit, preferably
from a car boasting a better standard rad.
What to Look For
When sourcing another radiator there are some key points to keep in mind:
Size
This is, um, the biggie! It’s most unlikely that the body opening in the
vehicle will allow the easy fitting of a radiator that is wider or taller, so
these dimensions should be measured from the original and assumed to be the
maximum. However, radiator depth can often be increased without running out of
space. Most radiators are what is called ‘twin row’. That is, when you look
inside the radiator cap opening you will see that there are two rows of tubes,
placed one behind the other. Other designs use ‘triple row’ designs (three rows)
and these are usually thicker. (However, the ‘row’ designation doesn’t tell you
all that much about size – some current radiators use only one row of (long,
thin) tubes that take up as much room as older ‘twin row’ designs.) So in
summary you’re unlikely to be able to go wider or taller but you might be able
to go thicker, possibly by moving to a rad with an extra row of tubes.
- Hose Tails Location and
Diameter
When you view the standard radiator from the engine bay side, where are the
hose connections? Some rads have hose connections on the same side; others have
hose connections arranged diagonally (for example, one hose connects to the
bottom left and the other to the top right). Some hoses connect at the end of
the tanks; others are set inwards perhaps a fifth of the width of the rad.
Without sourcing much longer hoses, you’ll need to keep the location of the
hose connections much the same as original, although the new connections can be
moved along the tank a bit – you just organise hoses with slightly differently
bends.
The diameters of the hose tails should be the same as original – sure, you
can get new hoses of different sizes, but these hoses still have to connect to
the engine – and not too many hoses have different diameters at each end...
Most radiators have a direct filling point, sealed by a pressurised cap.
However, other cooling systems have a pressurised remote filler tank. Again it’s
easiest to stick with the approach you already have. (Note that you should
always try to buy a capped radiator with the original specification cap in place
– having to buy a new cap could make a serious dent in your budget.)
If your car uses an automatic transmission, it’s almost a certainty that a
trans heat exchanger will be incorporated in the radiator. The heat exchanger
will be connected to the trans oil cooler lines with small diameter rubber hoses
– these are easy to see both on the original radiator and also on any new one
that you might be considering.
If the diameter of the hoses is similar, you can connect up to any heat exchanger location without too many probs – it’s dead easy to source longer hoses
(and if you live in a hot country, it’s also a good opportunity to add a trans
oil cooler – see Cooling the Trans).
So if you have a car with an auto trans, make sure that you buy a radiator from
another auto trans car.
If the donor rad comes compete with factory shrouded fans, that’s great!
However, it’s likely to cost you a lot more to source a rad with fans, so if
it’s going to be a case of swapping over the original shroud (engine driven fan)
or the shroud and fans (electric) to the replacement rad, don’t be too worried.
It’s also a good idea to check the original rad for sensors – some use up to
three to measure stuff like temperature (not just for fan on/off but also
sometimes to vary fan speed and even for the dash panel) and coolant level.
Unless you’re prepared to trade-off missing some of these functions (or adapt
new sensors in place of the old), if your original rad has a lot of sensors it’s
a good idea to forget everything I have written and go buy a new or
reconditioned factory replacement radiator.
Mounts
Unless you’re really lucky,
you’ll almost certainly have to make new mounts, so don’t get hung up on finding
a replacement rad with just the same mounting system.
Making the Choice
The best place to shop is a large wrecker that already has an array of
pulled-out radiators to browse through. It’s even better if they’re labelled so
that you know what cars they came from. In my experience, wreckers are vastly
cheaper than specialist radiator repair shops – even for identical,
unreconditioned rads.
In the case of the Maxima what I wanted was a radiator with these specs:
- A
maximum of 670 x 530 x 50mm (but extra depth ok)
- Hose
connections on top left and bottom right (as viewed from rear)
- Hose
diameters about 35mm
- As
many temp sensor screw-in positions as possible (original has two in rad and one
in a connecting coolant pipe)
- A
rad from a car at least as powerful as the estimated power of the modified car –
about 140kW
If your car was available in a more powerful model (for example you have a
six cylinder version and there was a V8 available), check if the more powerful
car had a larger radiator. This then becomes the obvious choice.
However, in some cases you can get even trickier. For example, the U12
Pintara (and Ford Corsair) has a body that under the skin, is very similar to my
older Maxima. So a radiator from one of these cars would more than likely fit
into the same body space. (Sure, these are four cylinder cars and mine is a V6,
but cars built specifically for Australia usually
have much larger radiators than similar imports. My Maxima is an import and the
Pintara/Corsair twins were made here in Oz.)
However, in this case when I examined the Pintara/Corsair radiators I found
that their hose positions are wrong for my application. I then narrowed the
search down to two wrecker radiators – a Holden/Isuzu Rodeo core that looked
nearly new, and an import
Toyota twin-turbo GZ20 Soarer rad.
Interestingly, a locally-delivered Cressida radiator – found next in line on the
rack – was near-identical to the Soarer design, but it wasn’t in such good
condition. The final nails in the coffin of the Rodeo radiator were a lack of
auto trans fluid cooler connections and a height which I thought might be just too tall. (And I wished I’d
measured the original radiator down to the millimetre - the variations in size
can be that tight!)
Having inspected the Soarer design closely for corrosion (none visible), fin
dents (a few minor ones), sensor locations (none, I would need to change some
aspects of the fan operation) I had the radiator costed and then walked away
with it for AUD$125. With a three month warranty.
Power vs Size
Before visiting the wrecker I was under the common impression that there was
a direct connection between the size of the radiator and the amount of engine
power available. After all, engine efficiency remains much the same irrespective
of power, so a more powerful engine always has to dissipate more kilowatts in the
coolant.
However, the relationship is nothing like as tight. For example, as indicated
in the main text, the Australian-built cars have disproportionately large
radiators – the Commodores and Falcons are cases in point. The JE Camira has a
radiator about twice the size of the contemporary Laser, while even cars like V6
Maximas and V6 Sonatas have quite thin and small designs.
Basically it’s our suggestion that while you should certainly be guided by
the power output of the car that you’re sourcing the donor radiator from, it’s
often best to simply use your eyes and go for the biggest design that you can
fit.
And another point – commercials often have larger radiators than normal
passenger cars.
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Fitting
The new Soarer radiator was a little narrower and shorter than the original
design. (Huh? He’s fitting a smaller
radiator? See ‘Power vs Size’ breakout above!) This meant that when the original
fan shroud (containing two electric fans) was offered up to the new radiator, it
overlapped the hose outlets a little. However using a hole saw, a belt sander
and a half round file soon created clearances for...
...the hoses...
...and also the drain cock...
...and the auto trans cooler hoses.
Some brackets were then bent up from aluminium strip to hold the shroud in
place.
The fan/shroud/radiator assembly then needed to be mounted in the car. In
nearly all cars, rubber mounts are used to locate the radiator. They’re rubber
for two main reasons – so that the rad can expand and contract without placing
stresses on its mounting points (and so developing internal stresses), and so
that the car can flex a little without breaking the radiator (all car bodywork
moves around a bit).
Typically, bottom mounts comprise rubber grommets located in brackets that
bolt to the bodywork. The radiator has a couple of prongs sticking out of the
bottom tank and these nestle in the grommets. The lower mounts support the
weight of the radiator. The upper mounts are normally rubber-bushed and their
main purpose is to stop the top of the radiator moving backwards or forwards –
they take little of the radiator weight.
In the case of the Maxima’s standard radiator, the system was a little
different. The lower mounts were threaded studs that bolted directly to the body
work, while the top mounts were rubber-bushed. However, the replacement Soarer
radiator used the more conventional mounting system.
New bottom mounts were therefore made from rectangular aluminium tube,
incorporating large grommets into which the Soarer’s lower tank plastic mounting
spikes sat.
Up the top, rubber mounts with projecting threaded studs were screwed into
the original mounting holes. These rubber mounts (arrowed) were previously
salvaged from the airflow meter on another car that was being wrecked. Brackets
were made from aluminium to connect the upper part of the radiator to the rubber
mounts. (In the final iteration slightly shorter rubber mounts were used –
again, salvaged from a wrecked car.)
The result of this mounting system is a radiator that’s well supported but
can still move slightly in any direction in its rubber mounts.
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When mounting the radiator it is important that the cap (or upper tank in
radiators without fillers) of the new design is maintained at the same height as
the original. That is, if the new radiator is shorter than the old one, the new
rad should be mounted with the extra space at the bottom, rather than at the
top. (The gap can be later filled with foam rubber to stop air bypassing the
core.) Radiators mounted lower than the original can create problems when trying
to bleed air from the system.
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Before the shroud was attached to the radiator for the final time, a seal
made from a foam rubber strip was installed. This was held in place with dobs of
contact adhesive. The seal ensures that all air that the fan draws is pulled
through the radiator – rather than from just around the edges of the shroud...
Those of you who are very observant and know Nissan Maxima turbos may realise
that the shroud and fans have been installed upside down. This was done so that
the fan with the longer motor ended up on the right-hand side of the car, so
creating more room near to the turbo. I did this in case I fit a larger turbo in
the future.
However, this inversion resulted in the fan wiring no longer reaching its
matching loom plugs, so the wiring was extended, as shown here. Note that as
fans typically draw a substantial amount of current, very heavy duty wire should
be used. Use the original wiring as a minimum sizing guide for the new conductor
thickness.
One new hose (arrowed) was needed as the top connection of the new radiator
was a little more towards the centre than the original. A piece of stiff wire
was bent into the shape of the required hose and then taken along to an auto
parts store to allow a comparison with all the moulded hoses available. The best
hose match required a short section cut off its end – easy with a hacksaw.
Sections of foam rubber were inserted either side of the radiator to prevent
airflow being able to make its way past the core. These were test-fitted (as
shown here) and then removed and rendered invisible by black spraypaint before
being reinstalled.
With the auto trans hoses reconnected to the heat exchanger and a few other
bits and pieces finished off (eg paint on the brackets), the installation of the
new radiator was finished.
Beware Bleeding!
When refiling the cooling system, be careful that bleeding instructions
provided by the car’s manufacturer are followed. This will usually consist of
turning on the heater and leaving the radiator cap off while the car is warming
up, filling the system as the level drops. However, in some cars an additional
bleed fitting will need to be opened to allow air to escape – if this is
required and it isn’t done, major cooling problems can result.
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Testing
In the case of the Maxima, further work was required so that the radiator
fans (now missing two of their temp switch inputs) would operate correctly.
However, this work will be covered in a separate story.
To make sure that the radiator itself was working correctly, the fans were
temporarily wired permanently on and the car taken for a hardworking test drive.
Even up the steepest of hills, the temp gauge barely moved past its ‘thermostat
open’ point (just under halfway) on the gauge. (Previously, even with the fans
running, the same test regime had had me cursing as the temp gauge rested just
under extreme hot.)
Overheating problem solved!
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