[Hiro]

Hi to all,

We are facing a severe problem here during vintage races:
The rear axle oil temperature rises up to 145°C in hot days,
So we need some kind of cooling set up.

Do you know of modern cars equipped with gearbox or diff cooler + oil pump,
That could be found in junkyards or Ebay?
Any idea welcome,
Including of course easy mods like finned axle cover etc.

Thanks for your help,
Hiro.

 

[baz]

i would think you could use a small carb electric fuel pump(i think it would be ok for oil) and an oil cooler mounted somewhere underneath then put 2 fittings in the diff cover 1 out 1 in you could even put a small filter in to keep the oil clean i would use a braided line for safety and maybe a dump switch for when the others get too close dont forget to prime the cooler then re fill for level

 

[nobody]

A carb pump won't work on hypoid oil. They are meant for low viscosity. You could use an auto tranny cooler but a pump may be a hard find in 12 volt. I'd look at places like Jegs or an equivilent racing supply place in your part of the world.

 

[jordan]

Whoa, I was worried there for a while becuase the differential on my gt after about 30 minutes of hard driving got up to 165ºf. at the hottest point (infared thermometer) I didn't see the "c" in 145ºc. and that is even under a race application.

 

[GTJIM (R.I.P.)]

Removing Heat

1) Reduce friction - are you using 'Redline' synthetic gear lube?

2) Increase cooling - use some ducting to get more air flow over the diff.
The alloy, finned, cover is a good idea - does anyone make one for the Opel diff?

 

[baz]

A carb pump won't work on hypoid oil. They are meant for low viscosity. You could use an auto tranny cooler but a pump may be a hard find in 12 volt. I'd look at places like Jegs or an equivilent racing supply place in your part of the world.

dave at 145°C would hypoid not be thin enough? i thought it would , maybe not

 

[nobody]

For gas they do a piston pump, same can be done for water. Above that you need a vane or variable vane type. I have an idea that I've used for oils but for a diff it would be sweet but design of it would require a good deal of rocket science. Let's just say an air pump and a check valve would be needed, but it could be placed anywhere as well as the cooler. Interesting, you would have a hard time with a 4 speed but with a rear diff and a 5 speed you could do them together with a cooler using all synthetic. I know, yet another wild idea.

Tell me if I'm off again. If you put pressure to a closed cylinder it will push fluid out. give it a good path out to a cooler and return it back through a check valve and then back to say the diff. Then again with a semi closed loop you could cool both tranny and rear diff if you were real creative. I'm thinking vent point right now, as a positive flow is fairly important.

Got you all lost yet?

 

[baz]

would 1 of those vane pumps you get for a drill work if hooked up to a small 12v motor ?

 

[GTJIM (R.I.P.)]

Kiss!

Before getting all complicated just increasing the air flow past the diff centre section should make a major improvement as the 'diff-erence' between a really hot day air temperature (35 C) and the diff oil temperature (145 C) is so great that heat transfer to the cooling air would not be too much of a problem!
You could always modify an air conditioning unit and blow all the cold air output past the diff/gearbox.....

 

[baz]

Before getting all complicated just increasing the air flow past the diff centre section should make a major improvement as the 'diff-erence' between a really hot day air temperature (35 C) and the diff oil temperature (145 C) is so great that heat transfer to the cooling air would not be too much of a problem!
You could always modify an air conditioning unit and blow all the cold air output past the diff/gearbox.....

'diff-erence' groan jim hang your head in shame
i see a lot of cars used for racing only that have a vent built into the side window and a flex tube through the rear floor to cool the diff
i will have to do it to mine when i get off my bottom and do something to it as it will have inboard discs to cool as well ,good job i have 1 broken side window now

 

[nobody]

Now your talking duty cycle and a drive motor for it too and mount. I was thinking what would be the easiest to get and plumb as well as reliability.

 

[baz]

duty cycle will depend on the normal length of 1 of hiros races and if it needs to run all the time
but i would have thought a stripped out 12volt drill motor and gearbox set to low speed and switched on when box gets hot (a water temp sender in diff cover and gauge to check it with ) would make a good fix (anyone know what the fail temp for hypoid is btw )
afraid you lost me when getting into closed cylinder stuff but i assume you are talking about an air driven high tech water lift pump like in a western film , 2 flapper valves on a piston that moves by air

 

[nobody]

Ok if you put a check valve on the vent on a later model diff you have a closed cylinder. Add some air pressure and the oil will go out or can be recirculated. I'd say 20 or 30 pounds would do it with a output and return line through a cooler. A constant duty small air pump is alot cheaper than an oil pump. You just have to pull the oil out on the bottom and back in the top. Vent it at the cooler and let it gravity feed back.....I'm all alone again aren't I

 

[kwilford]

Ok if you put a check valve on the vent on a later model diff you have a closed cylinder. Add some air pressure and the oil will go out or can be recirculated. I'd say 20 or 30 pounds would do it with a output and return line through a cooler. A constant duty small air pump is a lot cheaper than an oil pump. You just have to pull the oil out on the bottom and back in the top. Vent it at the cooler and let it gravity feed back.....I'm all alone again aren't I

No, we're just thinking...
The air pump sounds like an interesting idea. So does this happen intermittently? When you apply the pressure to the diff, the place where the oil goes has to be at a lower pressure than where it is coming from. So, maybe pressurize the diff, oil flows out the bottom and through a cooler to a reservoir that is vented and at a higher level than the diff . Then take the pressure off, and the oil drains back to the diff. Does this cause the diff level to fluctuate? Hmm, that can't be good. Or...?

Another concern might be that the pressure required in the diff pushes oil past the seals. If it takes 20 psi to push the oil out the diff and through the cooler to the reservoir, that might be enough to breach the seals.

I think it might be easier to just add a bunch of fins to the diff cover. They don't have to be aluminum. Just weld a number of rows of 1/8" steel fins, 1/2" tall or so, to the diff cover, on a 1/4" spacing, and that will increase it's cooling area substantially. If that isn't enough, add some ducting to move more airflow past the fins.

Although I have to wonder WHY the diff is running so hot. Is that normal among the racing crowd?

 

[baz]

Ok if you put a check valve on the vent on a later model diff you have a closed cylinder. Add some air pressure and the oil will go out or can be recirculated. I'd say 20 or 30 pounds would do it with a output and return line through a cooler. A constant duty small air pump is alot cheaper than an oil pump. You just have to pull the oil out on the bottom and back in the top. Vent it at the cooler and let it gravity feed back.....I'm all alone again aren't I

only thing i see wrong is that the oil will not drain into a pressurised diff(2-30 lb) from atmospheric pressure it would need to be pumped in so it would not work

 

[nobody]

Your right about the pressure differential issue. I was just looking at pumps and a 100 dollar air pump vs an 800 dollar oil pump was what made me think. although the idea of it being cyclic has merit to make it pump and drain back.

Ya the heat is too much, I was avoiding the simple idea that the bearings in the rear diff were probably gone. I've flogged my share and never seen one get that hot. I'm not sure what the thermal break down point of hypoid is.

 

[baz]

that drill pump is $18 and i think we all have an old battery drill in a cupboard that we hope we will find a battery for or a new case to fix the crack in the side
i had 1 more thought , if you use a thermo switch for a radiator cooling fan you have a 110c/230f auto cooler

 

[GTJIM (R.I.P.)]

Ancient Remedy ......

Just put a ring of tiny buckets around the back of the crown wheel - just like the devices the old Egyptians used to get water up out of the Nile - put a wee sheet metal trough under the top of the crown wheel with a drain out through the rear cover with a couple of finned cooling coils and run it back into the bottom of the rear cover. Perpetual oil motion ........ and cooling!!
Well - it would not work in reverse

 

[soybean (R.I.P.)]

Another concern might be that the pressure required in the diff pushes oil past the seals. If it takes 20 psi to push the oil out the diff and through the cooler to the reservoir, that might be enough to breach the seals.

I think it might be easier to just add a bunch of fins to the diff cover. They don't have to be aluminum. Just weld a number of rows of 1/8" steel fins, 1/2" tall or so, to the diff cover, on a 1/4" spacing, and that will increase it's cooling area substantially. If that isn't enough, add some ducting to move more airflow past the fins.

Although I have to wonder WHY the diff is running so hot. Is that normal among the racing crowd?

The idea in paragraph 2 seems to be the simplest and easiest to do because of the pressure and concerns of paragraph 1.
The question in paragraph 3, of which "Nobody" addressed, that the bearings in the rear diff were probably gone, might have a lot to do with the heating. Just a thought, Jarrell

 

[Hiro]

Thanks to all for your inputs!
I'll try to answer some questions and suggestions:

We have two kinds of vintage races here:
Some are very short (about 30mn each heat),
Others are "endurance" category (3 to 24 hours),
So of course our major concern is about the longer race.

As far as possible the set up should be:
- cost effective (yes we race our Opel with low budgets...)
- reliable (avoid too many switches and probes/relay etc)
- not to be turned on during the race (after oil gets hot enough to flow)

The idea about air pump is appealing,
But I'm afraid the gasket will not stand the pressure,
And the oil vent is required to release the pressure due to the "oil mist" inside the diff housing.

We have not yet tested high quality oils such as RedLine.
For the moment I use the cheap Motul PA90,
But I will try the RedLine stuffs as far as I don't race the longer heats,
So maybe it will be enough to solve my problem?

Next for me to test will be the finned diff cover + air ducts,
Here the Omega A has a finned alu cover,
So if this one fits our axle it's an easy swap to try.
Still looking for some cheap source about a strong oil pump.

Thanks for all,
Hiro.