External oil cooler kit? Options

[neilbardsley]

Lots very clean. Like the rubber connectors. I guess they dampen any vibration

[technicalninja]

If Chris puts his name on it, it's got my vote for sure. I am considering one of these for my /4, she runs around 210 - 220 on a hot day.

That’s perfect. Why would you change anything?! You don’t need additional oil cooling.

Zach

When I run at 85 or so MPH, she gets a bit over 230.

The horror (IMG:style_emoticons/default/shades.gif)

Lots of modern sports cars will push 250-270 under load and that’s with an oil to water cooler. Air cooled motorcycles pushed hard will run 300.

Trying to make air cooled engines run 180 under load is folly and isn’t even desirable.

Just my $0.02 based on decades of testing modern cars as a day job and messing with air cooled engines since I was a kid.

Zach nailed it.

(IMG:style_emoticons/default/agree.gif)
Unless you're running a dedicated track car at WOT you WANT the oil to hit at LEAST 220 to vaporize the moisture in it.

Most folks don't realize when you burn a gallon of gasoline you produce ALMOST a gallon of water vapor in the exhaust. Some of that get past the rings and will dilute the oil after time.

I would spec a 210/220degree T-sat on most street applications but ONLY AFTER installing both and accurate oil temp sender and an accurate CHT (on an aircooled) and verifying I needed the extra complication that an external oil system creates.

I'd want to see constant temps above 250 before I started adding coolers.
I would use fully synthetic oil as it has increased temperature resistance.
A short run up to 280-290 would not cause me to "shut down".

A streetcar that only hit 180 would bug the crap out of me.
It would require 3 times the oil changes that a 230 degree system needs.

OP, you are in England. I'd bet you don't need anything more than the stock cooler (a good one in clean shape) unless you were putting it under severe load for extended periods of time.
Properly diagnosis is the first step.

You need temp sensors and 4 hours of driving data before you need additional cooling...

[Superhawk996]

To double down on what Ninja posted, I think it’s important to provide sources so that you’re not just taking advice from a random lunatic on the web (referring to myself).

Excerpt below - sourced from Mackerle book on the engineering design principles of air cooled automotive engines; 1972 edition.

Note: modern oils have expanded the thermal performance envelope since this engineering book was published.

Note: The T4 engine does have an oil cooler that is completely adequate for stock engines.

Note: 110F= 230F ; 120C = 248F

[Superhawk996]

Probably time to roll this out again too.

Look at temperature gauge calibration and where the red zone begins. The OEM designed the gauges, engines were dyno tested for durability, etc. This is not speculation and internet mythology.

Note: OEM sender is the 200C sender. The other calibrations were provided to show how the gauge calibration changes due to vehicles having swapped oil temp sensors over the years due to ignorance or unavailability.

[technicalninja]

Note: modern oils have expanded the thermal performance envelope since this engineering book was published.

A Superhawk catch! An understatement...
Superhawk is NOT a "random lunitic"
His stuff is pretty good.
He's the first poster to provide the answer to your first question.

My first thought after reading his post was "Old info- numbers aren't right now-a days"

Read it again and find the disclaimer...

The Hawk snatches victory again!

My numbers today are 10-15 degrees C HIGHER.

At 280F oil temp I'd "abort the run" and select high engine speed and almost no load.
High cruise in 3rd or 4th.
If that didn't have nearly immediate temperature drop, I'd be worried.
Constantly touching 250 on every single drive would bother me.

One point to not forget. I live in N Texas. My outlook is in "hellish" conditions.
Weeks above 105 are common. I've seen 117 many times.
In England I would expect the 914 to need less cooling as you seldom exceeded 100F.
Am I right?
I've never been to England.
I assume England averages 20F cooler than Texas.

[930cabman]

250F is too hot for me, 210 - 230 is a good range

AFAIK engine speed/load are the main factors determining oil temp.

[neilbardsley]

If Chris puts his name on it, it's got my vote for sure. I am considering one of these for my /4, she runs around 210 - 220 on a hot day.

That’s perfect. Why would you change anything?! You don’t need additional oil cooling.

Zach

When I run at 85 or so MPH, she gets a bit over 230.

The horror (IMG:style_emoticons/default/shades.gif)

Lots of modern sports cars will push 250-270 under load and that’s with an oil to water cooler. Air cooled motorcycles pushed hard will run 300.

Trying to make air cooled engines run 180 under load is folly and isn’t even desirable.

Just my $0.02 based on decades of testing modern cars as a day job and messing with air cooled engines since I was a kid.

Zach nailed it.

(IMG:style_emoticons/default/agree.gif)
Unless you're running a dedicated track car at WOT you WANT the oil to hit at LEAST 220 to vaporize the moisture in it.

Most folks don't realize when you burn a gallon of gasoline you produce ALMOST a gallon of water vapor in the exhaust. Some of that get past the rings and will dilute the oil after time.

I would spec a 210/220degree T-sat on most street applications but ONLY AFTER installing both and accurate oil temp sender and an accurate CHT (on an aircooled) and verifying I needed the extra complication that an external oil system creates.

I'd want to see constant temps above 250 before I started adding coolers.
I would use fully synthetic oil as it has increased temperature resistance.
A short run up to 280-290 would not cause me to "shut down".

A streetcar that only hit 180 would bug the crap out of me.
It would require 3 times the oil changes that a 230 degree system needs.

OP, you are in England. I'd bet you don't need anything more than the stock cooler (a good one in clean shape) unless you were putting it under severe load for extended periods of time.
Properly diagnosis is the first step.

You need temp sensors and 4 hours of driving data before you need additional cooling...

I completely agree for most local journeys this is overkill.

Most take such short trips that don't get the oil warm enough.

However, here I'm talking about longer journeys. Like our drive to Florence last year. I would like to cruise at 180/210 not 220/250. I think that water will heat quicker than oil so the vapour will boil off before oil gets to 210?

[Superhawk996]

I think that water will heat quicker than oil so the vapour will boil off before oil gets to 210?

There is so much misunderstanding of oil and temps that it’s hard to get folks to forget what they were told by grandpa, their father, or what they have read for years.

The problem is that 180F oil will not “boil” off water condensed in the oil. Not to be pedantic but water boils at 212F (sea level). So no, water will not boil water off and out of oil at 180F.

In fact oil at 180F oil promotes condensation in a running engine.

Why?

As Ninja stated, you have water vapor (212F +) entering the crankcase as ring blow by. The temperature of that water vapor is well above 212F.

So now that hot water vapor hits 180F oil in the case. What happens?

If you said that the hot water vapor condenses, onto, and because of the cool 180F oil you would be correct.

So not only are you not removing water vapor at 180F, you are promoting condensation into it.

I know that I’ll not likely change anyone’s mind that has already made it up based on mythology but physics is physics and it doesn’t change based on personal opinions.

[Superhawk996]

Here is what happens to an engine that has been run too cold with excessive condensation causing rust up in the oil breather.





As always, it’s your car and your decision what to do based on personal opinion. Bear in mind that physics doesn’t care, and there are consequences to not running oil hot enough to drive out the condensation.

[ChrisFoley]

In my experience on the race track, continuous operating at oil temps much above 225F was detrimental to oil pressure. Not sure if it was change in viscosity or larger bearing clearances or some combination of the two.

[Superhawk996]

In my experience on the race track, continuous operating at oil temps much above 225F was detrimental to oil pressure. Not sure if it was change in viscosity or larger bearing clearances or some combination of the two.

Within limits viscosity can be addressed. When I used to crew, it was common to run thicker oil to account for the viscosity loss. The problem was on cool mornings that meant heating the oil sump and the engine block before starting to keep from starving the bearings when oil was cold. It’s all just trade-offs.

Regarding gauge pressure - it isn’t the be all end all. As long as there is sufficient oil being supplied to the bearing, the hydrodynamic oil wedge will be maintained and the bearing and crank will be protected.

To put some numbers to this, if oil pressure is nominally 60 psi at 5000 rpm with 210F oil, and things get hot, oil viscosity decreases and oil pressure (gauge) drops to 50 psi, there will still be plenty of hydrodynamic pressure within the bearing to support the crank loads.

If on the other hand the supply pressure (gauge) drops to 25 psi at 5500 RPM, sure there is going to be a loss of the oil wedge and increased bearing and/or crank wear.

This is getting pretty far off topic into the realm of racing, high engine loads, and RPMs that most engines only see momentarily. I don’t mean to discount your observation on track.

However, track use shouldn’t be taken to be the same as street use of extend high speed driving at legal posted limits plus some long arm of the law fudge factor.

Anecdotally my 1st 914 was a 1911cc and I used to cruise at 80-85. Midwest summer temps into 90s and low triple digit are the norm. Stock oil cooler. That engine ran 100k miles. Was it down on power at the end? Sure, but what engine isn’t by then.

[technicalninja]

Superhawk's pictures and diagrams are worth a thousand words...
(IMG:style_emoticons/default/first.gif)

ChrisFoley's car is a "science project" into thermodynamics...

One of his better mods is what I refer to as the "racoon habitrail".

He's got a tube, a BIG one, running from the front of the car through the passenger compartment and ending at the entrance to the engine fan.
A racoon would fit!

Big ass tube helps in many ways, all of them related to cooling...

[black73]

Here is what happens to an engine that has been run too cold with excessive condensation causing rust up in the oil breather.

Fact or opinion? How do you verify that to be the cause?


A little different take from the Bob Is The Oil Guy forum.

[neilbardsley]

I think that water will heat quicker than oil so the vapour will boil off before oil gets to 210?

There is so much misunderstanding of oil and temps that it’s hard to get folks to forget what they were told by grandpa, their father, or what they have read for years.

The problem is that 180F oil will not “boil” off water condensed in the oil. Not to be pedantic but water boils at 212F (sea level). So no, water will not boil water off and out of oil at 180F.

In fact oil at 180F oil promotes condensation in a running engine.

Why?

As Ninja stated, you have water vapor (212F +) entering the crankcase as ring blow by. The temperature of that water vapor is well above 212F.

So now that hot water vapor hits 180F oil in the case. What happens?

If you said that the hot water vapor condenses, onto, and because of the cool 180F oil you would be correct.

So not only are you not removing water vapor at 180F, you are promoting condensation into it.

I know that I’ll not likely change anyone’s mind that has already made it up based on mythology but physics is physics and it doesn’t change based on personal opinions.

I'm aware that water doesn't boil below it boiling point but for oil to heat up to 180 there is a temperature source that is hotter? I'm just claiming the water will heat up quicker than oil and boil off before the oil gets to 210?

[neilbardsley]

In my experience on the race track, continuous operating at oil temps much above 225F was detrimental to oil pressure. Not sure if it was change in viscosity or larger bearing clearances or some combination of the two.

This is to do with oil quality. The stability/viscosity index is only measured to 100c so it not a good measure of stability at higher temperatures.

If you look at Motul's 300v racing oil they state the viscosity at 150c. I believe you want a figure above 4. This is where good modern synthetic oil will out performance a mineral.

https://raceandrally.com/motul-300v-chrono-...g-engine-oil-2l

[Superhawk996]

I'm aware that water doesn't boil below it boiling point but for oil to heat up to 180 there is a temperature source that is hotter? I'm just claiming the water will heat up quicker than oil and boil off before the oil gets to 210?

I’m not sure I understand your question.

One fluid does not warm faster than the other. If we have oil and water mixed (emulsified) and heat the fluid, the whole fluid heats at a uniform rate. Even if the oil and water were not emulsified and the two are separated into layers, both layers will heat at a uniform rate. As the fluid approaches the boiling point of water, yes, the water will boil, turn into vapor, and it will eventually be boiled off at which point the temperature of the oil can rise past 212F once the temperature water is expelled.

Don’t try this at home. Hopefully everyone has experienced the effect of a drop of water entering hot oil above 212F. It immediately vaporizes the water and that light, rapidly expanding vapor is explosively expelled from the oil. Very dangerous.

Setting aside boiling temp, vapor pressure, evaporation, etc., it is a question of equilibrium. If water vapor is entering the oil quicker than it can be expelled, oil sludges and emulsifies. It is an established fact that the hotter the oil is run, the less risk there is of sludging and oil contamination by water, and even fuel if run rich enough and cool enough.

The thing that is so odd to me is why so many try to make an air cooled engine run oil at 180F when their daily driver, modern car isn’t running at 180F. (IMG:style_emoticons/default/confused24.gif)

[Superhawk996]

Here is what happens to an engine that has been run too cold with excessive condensation causing rust up in the oil breather.

Fact or opinion? How do you verify that to be the cause?

That engine when torn down was run without cooling flaps and with a cobbled deflector to the oil cooler. This caused the engine and oil to have extended warm up and to run cooler than it was designed to run. I don’t know the drive cycles it was subject to. However, if this was run infrequently and run on short trips, that would only make matters worse. Based on the amount of rust and sludge that was in the sump, and the condition of the breather, I’d guess lots of short trips.

For those old enough to recall the 80’s, removal of cooling flaps was a “fix” applied to many 914’s that were thought to be running hot by well meaning but misguided folks that tried to make air cooled engines run at the same oil temps as water pumpers.

Removal of cooling flaps not only results in delayed initial warm up, but overheating at high load because the oil cooler airflow is practically non-existent.

When some finally realized that these engines are actually air AND oil cooled, they got even more creative (in the case of this engine) and removed the flaps but made a deflector to force air to get the cooler at all times - presumably to avoid the aforementioned tendency to overheat under high load.

The 80s and 90s generally were not kind to 914’s. Lots of these cars end up in the hands of people that didn’t understand air cooling and whom were too broke to maintain them properly. They were considered cheap and disposable.

[neilbardsley]

I'm aware that water doesn't boil below it boiling point but for oil to heat up to 180 there is a temperature source that is hotter? I'm just claiming the water will heat up quicker than oil and boil off before the oil gets to 210?

I’m not sure I understand your question.

One fluid does not warm faster than the other. If we have oil and water mixed (emulsified) and heat the fluid, the whole fluid heats at a uniform rate. Even if the oil and water were not emulsified and the two are separated into layers, both layers will heat at a uniform rate. As the fluid approaches the boiling point of water, yes, the water will boil, turn into vapor, and it will eventually be boiled off at which point the temperature of the oil can rise past 212F once the temperature water is expelled.

Don’t try this at home. Hopefully everyone has experienced the effect of a drop of water entering hot oil above 212F. It immediately vaporizes the water and that light, rapidly expanding vapor is explosively expelled from the oil. Very dangerous.

Setting aside boiling temp, vapor pressure, evaporation, etc., it is a question of equilibrium. If water vapor is entering the oil quicker than it can be expelled, oil sludges and emulsifies. It is an established fact that the hotter the oil is run, the less risk there is of sludging and oil contamination by water, and even fuel if run rich enough and cool enough.

The thing that is so odd to me is why so many try to make an air cooled engine run oil at 180F when their daily driver, modern car isn’t running at 180F. (IMG:style_emoticons/default/confused24.gif)

I take it back. It water needs more energy input than oil to heat.

[GregAmy]

We have similar discussions in General Aviation flying circles. They may be 360 cubic inches (or 320, or 540, or whatever) but they're just big air-cooled engines.

The general mindset is that you don't want to fire it up unless you're going to fly it. The general rule of thumb is to get the oil to at least 180 degrees* and run it for a half hour. I've seen some smaller Lycoming engines where someone loved to do short trips, like fire up his airplane after work each day for a few trips around the pattern, and it had crusty stuff like the above (his condensate relief tube was actually blocked).

I actually use that rule-of-thumb in all my cars, 914 and otherwise. I'll push any car around in the drive/garage instead of quick-firing to move it. Just gives my brain the crusties firing up a car and shutting it down 30 seconds later.

So here is your reason for randomly grabbing the keys and taking nice long drives in the 914: it's for dependability, improved service, reduced repairs, reduced costs, and ultimately, for the safety of children everywhere and of mankind as a whole.

You are doing a great service for this country. Thank you. - GA

* You don't have to "boil off" the condensation at 212, it'll evaporate just fine at lower temps, it just takes longer. Ask the sweat glands on your arm if you disagree...

[neilbardsley]

We have similar discussions in General Aviation flying circles. They may be 360 cubic inches (or 320, or 540, or whatever) but they're just big air-cooled engines.

The general mindset is that you don't want to fire it up unless you're going to fly it. The general rule of thumb is to get the oil to at least 180 degrees* and run it for a half hour. I've seen some smaller Lycoming engines where someone loved to do short trips, like fire up his airplane after work each day for a few trips around the pattern, and it had crusty stuff like the above (his condensate relief tube was actually blocked).

I actually use that rule-of-thumb in all my cars, 914 and otherwise. I'll push any car around in the drive/garage instead of quick-firing to move it. Just gives my brain the crusties firing up a car and shutting it down 30 seconds later.

So here is your reason for randomly grabbing the keys and taking nice long drives in the 914: it's for dependability, improved service, reduced repairs, reduced costs, and ultimately, for the safety of children everywhere and of mankind as a whole.

You are doing a great service for this country. Thank you. - GA

* You don't have to "boil off" the condensation at 212, it'll evaporate just fine at lower temps, it just takes longer. Ask the sweat glands on your arm if you disagree...

Thank you. Your point is well made. More wear on the engine at startup than other times. Impact I've started to not press/pump the gas pedal after mine has been sitting for a bit so that some oil can circulate before the engine starts