Oil Coolers And Cylinder Head Temps - Real Time Experiences

[Fasterbrit]

Ok, there's been a whole lot of talk, and even more written matter on the subject of oil coolers and there merits on aircooled' VWs. Most of it suggest that oil coolers do nothing other than reduce the oil temp and little heat reduction in any other areas. Now, I have never really subscribed to this logic as it doesn't  compute. Reducing the temp of oil should reduce the temp of the components it flows over, surely? Well, I thoght I'd do some real time testing and record some data.

Firstly, the motor in question: a 2007cc Type One Turbo that produces 260 hp on the dyno and runs low 14 second quarters in a full camper Split Bus. Comp ratio is 7.5:1 and runs stock VW cooling, but no VW oil cooler to reduce latent heat in the fanshroud. Instead we ran a large Messa oil cooler with fan situated between the chassis rails. Now this motor has been given death for the last five years visiting many shows and drag strips across Europe. At a steady cruising speed of 80 mph (sat nav verified) the oil temps stabilise on a 80f degree heat day to 210f. Cylinder head temps were stabilised at 300-310f. Now when the Van was given lots of right foot, the temps of both oil and heads would rise quickly. This was never really a problem as as soon as you backed off the temps would drop and stabilise quickly. This got us thinking as to the merits of a second Messa oil cooler, which was duly fitted and given the same circumstances and conditions for test purposes. The results were quite startling - the oil temps will not budge higher than 180f. Cylinder heads would stabilise at 260-280f. Bear in mind this is a heavy vehicle (1500kg), so works very hard. This test is not a one-off fluke as the Van is driven regularly and HARD!

Anyone have similar experiences to prove the connection with oil and head temps?   

[Martin]

Just think how much oil is being sloshed about in the rocker box's. stand to reason that if the oil is cooler than the heads the oil will take on the heat from the heads.

just out of interest, are you measuring the head temp of 1&2 or 3&4?. I suspect 3&4 may be running a little cooler than 1&2 as it will have much more oil in it past 4000 rpm



Martin

[Phil West]

Hi Matt,

After years of readings while towing - my 96 plate cooler with fan keeps oil temps at 180F on flat road with head temp (sensor in #3) at 300F.  Up long hills the oil climbs to 190 and heads to 330.  I kept the stock oil cooler.  So oil always runs at about optimum temp but heads are HOT!  So I don't believe adding another cooler would do much for my head temps.  The differential in temps between oil and head is 120 to 140F so the oil is only doing partial cooling from the rocker space.  Does removing the stock cooler really reduce differential heating in the fanshroud area?  I thought VW spent enough money on the doghouse r&d to ensure a negligble loss in cooling.  Anyway the question remains - how to control head temps even though oil is operating at optimum temps.  Fitting the smaller top pulley lost 20-30F on the heads.  I suppose Porsche cooling would increase air flow over the heads.  I have yet to do the air pressure test on the engine bay so I don't know for sure whether I have +ve or -ve pressure in there.

Cheers
Phil

[Fasterbrit]

Marty - the temp sensor is on no3
Phil, I know where you are coming from on VW and r+d and it makes sense, but the dog house takes approx 200 cfm of air, so if removed, there is that extra amount of air which has nowhere to go other than over the heads and cylinders. There is also the latent heat issue from the stock oil cooler inside the fanshroud which will always transfer heat, albeit small. But as heat rise is exponential, every little bit helps.
Whilst on the subject of VW r and d - I remember reading that the air intake louvres actually begin to rob air from the engine bay above 60 mph. With this in mind we ducted air from a high pressure area to the fan intake (2x 2" hoses) and this made a considerable difference to cool runnings on the same Split Bus - particularly on head temps.

Also, for every one degree decrease on air intake into the carbs, your exhaust temp reduces by the same amount, as does combustion chamber temp. The bonus of this is to also increase power and economy due to extracting the most amount of heat energy from your fuel. W

[Zach Gomulka]

I believe that oil will take some heat out of the heads, but it is not the solution for hot running heads!

[Rasser]

I like the idea of removing the factory oilcooler, and replacing it with an external cooler (ex. mesa style with fan). As you say, by removing the factory cooler, much more air will be pushed down over the heads and cylinders.
I did the same thing with my type4 engine. External oilcooler, LATE STYLE 36hp fanshroud with the wide fan.

If anything should help cool the heads, then it would be getting more air down through the cooling tins. Then you can always buy as big an oilcooler as you need, to keep the oiltemps down at a reasonable level.

I can´t see why people use both the factory oilcooler + an external. I would much rather use a little extra airflow down thorugh the heads and cylinders, and only use an efficient external oilcooler.

[Bruce]

I can´t see why people use both the factory oilcooler + an external. I would much rather use a little extra airflow down thorugh the heads and cylinders, and only use an efficient external oilcooler.

If you take the stock cooler out, you'll get more air flow to the left 2 cylinders.  It won't increase the flow on the right.

[Fasterbrit]

I can´t see why people use both the factory oilcooler + an external. I would much rather use a little extra airflow down thorugh the heads and cylinders, and only use an efficient external oilcooler.

If you take the stock cooler out, you'll get more air flow to the left 2 cylinders.  It won't increase the flow on the right.

This is only true if you continue to use the stock doghouse fanshroud. Use a non-doghouse and air flow will be equal.

[Jon]

Second Law of Thermodynamics: Heat Travels from Hot to Cold Bodies
If you can get the oil temperature down it will suck heat out the heads, I know of a guy who claims that he cools his type4 with only oil cooling, but the engine sits in a buggy so airspeed plays a role too I bet.

[Torben Alstrup]

Yes, the fan shroud has to be a late version. A "simple" 30hp shroud will do what Bruce said.
Ram cooling and oil cooling is basically what the Trike people do. (On the Eu side) because the engine sits in front of the transmission. In a buggy it woild need some deflectors to get sufficient air to the engine. But absolutely doable if you absolutely want.
T

[Bruce]

Use a non-doghouse and air flow will be equal.

What testing did you do to determine that?

[BeetleBug]

Very interesting thread, thanks.

One question, have anyone noticed any difference in head temps switching from gasoline to E85?

Best rgs
BB

[BeetleBug]

Second Law of Thermodynamics: Heat Travels from Hot to Cold Bodies
If you can get the oil temperature down it will suck heat out the heads, I know of a guy who claims that he cools his type4 with only oil cooling, but the engine sits in a buggy so airspeed plays a role too I bet.

True, he said he drives his buggy everywhere and in any weather with no fan at all, just several oil coolers. On the other hand, all the trikes do the same thing. No fan at all and only a very small oil cooler mounted in "the wind"

Best rgs
BB

[Fasterbrit]

Use a non-doghouse and air flow will be equal.

What testing did you do to determine that?

just the monitoring of head temps, which dropped when switched to non doghouse without oil cooler. I don't have the facilities to measure air flow, but road testing suggests positive results.

Another issue which will raise much debate is that of using fully synthetic oil. I always find engines run cooler on fully synth. Again, the laws of physics apply here: friction equals heat - less friction; less heat. Simple. Some people argue that synth oil transfers less heat due to it's molecular structure, but again road testing for me is by far the best diagnostic tool. 

[Phil West]

Well from what I'm reading I may have to remove the doghouse cooler and see what happens to head temp (and to oil temps).  Useful for me as the sensor is right in #3 so if the cooler is robbing cooling from #3 head I should see a diff.  I'll leave the doghouse fanshroud to begin with.  Once I have seen what happens to temps - hopefully down - I might even try a non doghouse to see if it makes a diff.  I'll need to drop the motor so whenever that next is.....

Do you have any test data to back up fully synth oil being better at removing heat than mineral oil?  As you say I thought it wouldn't be as efficient at drawing heat away.

[Fasterbrit]

Phil, fully synth is no better at drawing heat away than mineral oil, it's the fact that LESS heat is created in the first place due to less considerably less friction. My advice would be NOT to keep a doghouse style fanshroud if you remove the oil cooler. You need a 1600 style non doghouse fanshroud. If you run dh without the cooler present, you WILL have uneven airflow due to the internal vane design.