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The mkiv Supra Owners Club

MKIV Oil Cooler Kit


Guest Ash
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I'll shortly be looking into the oil-cooler question with a view to coming up with a kit of parts. The kit will initially be fitted to Justin's engine that will be used as a test-bed for the conversion.

 

The oil has a *very* tough time in the MKIV. I remember one particularly quick blast across France turned my just renewed Mobil 1 to treacle after less than a thousand miles. Now, having had the chance to look at the internal components of Justin's engine, I am utterly convinced of the importance of using quality oil and changing it regularly. At *least* every 3000 miles.

 

The reason why the oil has such a tough time is because of the sheer amount of heat it has to sink.

 

Consider that, in an internal combustion engine, oil is the primary cooling medium - not water as many lay-persons assume. With the MKIV, oil jets under the pistons don't just squirt oil at the back of the pistons willy-nilly... they actually mate with a channel that is bored into the piston which circulates around the underneath of the piston crown. In other words, runaway oil temperatures can directly lead to runaway piston crown temperatures too.  

 

Oil also has a very tough time keeping the turbo bearing housing cool. Cooling in this area is supplemented by water, but it is the *oil* that is in direct contact with the turbine shaft. It is amazing to think that just a few millimetres from this oil flow is a turbine spinning at up to 130,000 rpm at a temperature that can reach over 900 degC.

 

Sitting in the exhaust flow are the exhaust valve heads. The thing that stops them heating up to the point of destruction is the valve stem; which conducts the fierce heat, induced by the exhaust, directly into the valve guide. The camshaft end of the valve guide is awash with oil, which cools the guide and in turn cools the valve stem and ultimately the exhaust valve head itself.

 

In a tuned engine, I have witnessed how the MKIV oil temperature soars under full boost: even to over 130 degC. and that was on a fairly cool day.

 

To my mind, it is not a question of whether or not the oil itself can take this kind of temperature. The important question is what potential damage could be caused to the engine (not to mention the power loss) as a result of this runaway heat?    

 

I have often said that designing a properly tuned forced induction engine is all to do with good heat management. To my mind, being that oil is the primary coolant, it is therefore essential that the oil temperature is held stable under all engine conditions and over a wide range of ambient temperature.  

 

To succeed in this aim, as I say, Justin and myself will shortly be developing an oil-cooler kit. I'm not sure yet on prices but if you are interested in buying one and/or having one fitted then I'd be gratefull if you could e-mail me privately in order to register your interest. Obviously, the more people that want one then the cheaper we can source the parts.

 

Yours,

J

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As an aside from my direct email on this subject, doesn't the Slurpa already have an oil cooler (genuine question, not rhetorical, some might not)? What's wrong with the stock cooler?

 

I had thought that, as my car was designed to operate in temperatures of around 90-100 deg C and humidity of 85+%, i.e., Japan, it would be well OK for fast road use in the UK.

 

 

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You are quite correct. Both the UK and the J-Spec cars have what Toyota describe as an oil cooler. It is a small oil-to-water unit sandwiched between the oil-filter mounting flange and the filter itself. For a bog-stock car that arrangement is just about adequate, and actually provides a useful dual function.

 

Most members will be aware that the direction of thermal transfer in a heat exchanger, is from the higher heat side into the lower heat side. Initially, as the water heats up much faster than oil, the water will readily give up a proportion of its heat into the cooler oil. In other words, what is described by Toyota as an oil-cooler actually turns into an oil-heater when starting up from cold. This has the *very* beneficial effect of bringing the oil up-to-temperature much faster. Which is a darned good thing *especially* on a turbocharged engine.  

 

Problem is, for a heat exchanger to operate with any significant degree of efficiency, there must be a fairly wide difference between the temperature on one side of the heat exchanger -versus- the temperature on the other side. Generally, the greater this difference in temperature then the greater will be the efficiency of the intercooler.

 

Drag cars, and the like, have water sprays, fed from a tank of iced water, that spray a fine mist of water at the intercooler in order to get it as cool as possible. What they are basically doing, in effect, is getting as much of a differential in temperature: between the intake charge on the inside, and the ambient air on the outside. This has the effect of *significantly* increasing the efficiency of the heat exchanger.

 

The problem in the case of the MKIV is that the normal operating temperature of the water is about 90 degC and the optimum operating temperature of the oil *should* be in the region of 90-110 degC. First thing I note here is the relatively small temperature difference between the two. This will have the effect of significantly *reducing* the efficiency of the oil-cooler... just when we begin to most need it!

 

Of course, as the temperature of the oil rises, say, to 130 degC and above then the efficiency of the oil cooler will increase - due to the greater temperature differential, i.e. 90 degsC water and 130+ degsC oil. But by this stage we have already exceeded our maximum sump temperature (110degs) by 20 degrees... and rising!

 

Ideally, what would be nice is to keep the same initial situation, where we get a speedy oil warm-up. But once the oil came up to temperature then the cooling water, flowing through the oil cooler, should be switched in some way and be made to flow through a front mounted radiator before being fed to the oil-to-water heat exchanger.

 

Doing this would *significantly* increase the temperature differential between the two sides of the heat exchanger. Now, the oil would be flowing at a temperature of 90-110 degC as before. But the water, rather than being at normal engine temperature of around 90 degC, would be sitting somewhere in the region of 10 degrees above ambient temperature (depending on the size and/or efficiency of the front-mounted cooling radiator). Typically, in the summer, around 30 degC. This greatly increased difference in differential temperature would, in turn, greatly increase the efficiency of the oil-to-water oil cooler.

 

Another way would be to retain the stock oil-to-water cooler and to have an additional oil circuit that would switch-in, at a certain sump temperature, and allow oil to flow through a supplementary oil-to-air cooling radiator situated at the front of the car. There is a slight problem with this in the sense you are asking the oil to flow through quite a large additional circuit. Some loss in oil pressure is inevitable. Whether such loss is of any significance will remain to be seen, and can be minimised through the use of pipes of a larger bore, say, three-quarter inch. And ensuring any 90 degree turns are made in a gentle swept bend, rather than a sharp corner. Plus, there will be a degredation in the overall integrity of the oil system due to the front-mounted radiator. Which can be subject to damage leading to possible loss of oil pressure at high engine speed. Protection against possible damage will, of course, have to be built into the actual design.

 

Personally, I prefer the first approach as it has the advantage of leaving the oil-circuit completely stock. But the stock oil-to-water unit is rather small. Whether it will have the necessary heat-sinking capacity, even with a reduction in water temperature, remains to be seen.

 

If you are running a bog-stock car, that poodles around in traffic most of the time and only gets the odd spell of full throttle action and never sees a track, and gets regular oil and filter changes using a quality synthetic oil, and so forth. I can say, quite categorically, that fitting any kind of additional oil-cooing would be a complete waste of time.

 

However, you need to bear in mind that whilst there are components and/or systems on MKIV that have an in-built strength and/or capacity that go way beyond what would ordinarily be experienced with a stock car (the block, for example, is bloody strong; likewise with the crank; pistons; connecting rods: all these components have a capacity to deliver a power output that is significantly greater than the power developed as stock) there are those components and/or systems that could could be said to be marginal.

 

Unfortunately, oil cooling is one of them.

 

Once you remove the protection of fuel cut and wind up the boost, and sustain that boost for any significant period of time, like on a track-day for example, or a blast to Paris and back... oil temperatures go through the roof.  

 

Yours,

J

 

 

(Edited by Ash at 1:35 pm on June 24, 2001)

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Hi...

 

Interesting ideas although to the lay man it sounds rather complicated and probably expensive. I'm no expert but, wouldn't it just be easier to add an additional stat based oil cooler and enjoy the benefits of a quick warm up the stock cooler and temp control from the extra cooler when required.  

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Sorry to be going over your head a little, Gavin, but the one big advantage of this forum is the ability to have different sections.

 

The section here *is* a technical one... where it goes without saying that technical stuff can be readily discussed.

 

There are bolt-on, oil-to-air cooler conversions on the market which you may be interested in. Perhaps the most popular is the one produced by HKS. However, as with most bolt-on conversions, there are *always* other factors to consider.

 

What is being *primarily* considered on this thread, are oil-cooler conversions that can be tailored to specific engine requirements, with a high degree of technical study allied to their design.  

 

It's kinda like someone buying an off-the-peg suit and making do... or having a suit tailor-made.

 

Yours,

J

 

(Edited by Ash at 9:23 pm on June 24, 2001)

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.....or a blast to Paris and back... oil temperatures go through the roof.  

 

Yours,

J

 

...or a blast to Eindhoven and back, after which Powerstation complained my oil smelled cooked. Got it!

 

I too would have been happier if you had said oil-air coolers would do the job if...............; as they are so much easier to deal with.

 

You've got me totally paranoid now as I won't go near power increase mods until:

(a) the brakes are as good as they can be for the power increase anticipated, e.g. for a Nur spec exhaust new induction and cat removal = carbon pads and new discs (that reminds me, I owe Mr. Whifin a visit).

(b) the engine is actually operating more efficiently and has had any/all new stresses accommodated, e.g. oil is highest priority in this section.

 

If, as you say, the oil system is already marginal, I'm considering not even switching it on again until I've fixed that.

 

Finally, (Ash), why are you wasting time reading this and not working on delivering the solution?

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LOL........

 

I'm working with Justin on a couple of engine issues. Once they are sorted, I can get his lump back where it belongs and use it as a test-bed for the oil cooler.

 

I know what you mean by the word: cooked. Yep, I know that smell only too well.

 

An external oil-to-air-cooler I am sure will do the job easily enough (as that is the cheapest solution). But the piping will have to be of a large enough diameter in order not to significantly reduce the flow. My latest flow calculations suggest that 18mm bore will be adequate. Such a diameter is readily available so no problems there.

 

I need to look at the oil take-off in a little more detail.

 

To my mind, it would be doubly beneficial to fit a remote oil filter as, not only will it be easier to replace, the actual filter could be enlarged as much as possible... thus giving a useful increase in flow over the stock filter.

 

Trust me, you'll be one of the first to know of our developments.

 

Yours,

J

 

 

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I know how easy it is to get remote filters wrong. We fitted a high compression V8 into an ex-army lightweight Land Rover about 25 years ago (not one of those wussy low compression jobs they fitted to the Range rover). Added a Salisbury rear axle, etc.

 

Almost all custom items (hybrid flywheel, etc.) were precision machined by British Aerospace, thanks to a 'friend', but the necessary remote oil filter was a "that should be an adequate bore" job.

The bends did not have a sufficiently large angle nor were they adequately polished internally. The first time we took it out in anger, for a prolonged period, it dumped all the bearing surfaces.

Fortunately, my friends at Hamer Stevenson, determined the best solution in braided flexible hoses and, after we'd renewed every bearing surface above the sump, we never had another problem.

 

Lesson well learned!

My inclination is to listen to what is 'sure' to be safe and then find the hose size 2 up from that one.

 

And see, you're still wasting time again.......

 

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Double LOL.........

 

Hey, it's after 12 and from midnight to 1am is about the only hour I ever get to myself. :)

 

Best wishes buddy,

J

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Double LOL.........

 

Hey, it's after 12 and from midnight to 1am is about the only hour I ever get to myself. :)

 

Best wishes buddy,

J

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