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Auxiliary Cooling Oil to Coolant Coolers **** Large Post w

#1 User is offline   Daless2 

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Posted 05 January 2004 - 08:52 PM

Auxiliary Cooling – Oil to Coolant Coolers **** Large Post with Graphics

If you haven’t already figured it out I have this fixation about cooling and under hood temperature management. Fortunately for me my friend Kevin owns an automotive test lab and is kind enough to let me use some of his specialty equipment to do these kinds of things.

Thanks Kevin!

If you have an interest, here are some related threads on this forum dealing with Temperature Management.

Auxiliary Cooling – Hood Louvers / Vents.

Coolant Temp Testing: Fan/Clutch vs. Flex-A-Lite 475 Electric Fan.

Managing York OBA Temperatures.

This one, while not temperature related does have a little bit of info on oil filter effectiveness. You might find it interesting.

Oil Filtering Effectiveness - Fram/Napa/Pure1/Mobil1/OilGuard.

What is an Oil to Coolant Cooler?

Glade you asked!

Here's a picture from the front side.

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And here’s another from the backside.

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How Does it Work?

This oil cooler, like all others is a heat exchanged.

This design incorporates a honeycomb oil passageway inside which is surrounded by a chamber in which engine coolant is pumped through.

The Oil to Coolant Cooler is sandwiched between the engine bock and the engine oil filter.

Unlike conventional oil coolers, hot oil in this design never really leaves the engine to any great extent while being cooled.

Visualize this while looking at the two pictures I posted above. The “Cooler” bolts to the engine block where the oil filter would normally go. The oil filter then spins onto the “cooler”.

When the engine oil pump pushed hot oil out to be filter it first has to go through this unit to be cooled a few degrees before reaching the filter.

After being filtered, the clean oil has to travel back through this cooler, where more heat is removed, prior to the clean oil entering the engine.

Here is a picture of what this unit looks like with an oil filter attached.

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Take a look at the two hose nipples.

This cooler has two hose connections on it that attach, inline with the heater core return hose.

The engine water pump continuously pushes a flow of coolant from the engine to the heater core and back to the engine. This happens on the TJ 4.0L engine (and most others) independent of the heater selector controls in the cab.

The Oil to Coolant Cooler taps into the heater core return line. Basically you cut the line and attach one end to one hose nipple on the cooler, and the other end of the heater core return hoes to the second nipple on the cooler.

Once your engine is warmed up to operating temperatures, the Coolant Temperatures” are significantly LOWER then your engines “Oil Temperatures”. It is this temperature differential that enables the “Cooling of the Oil” and creates a closer equilibrium with your engine between the oil (which is also cooling the engine) and the coolant.

How Well Does it Work?

I did quite a bit of testing on this during the dog days of the summer. I will share with you how I did this and the results of my testing. I have my own conclusions based on this testing effort.

You are welcome to form your own, but I will tell you right now, I was able to lower the average temperature of my engine oil by a little more then 14 degrees F.

Testing Methodology

Here’s how I did the testing.

Prior to testing the Oil to Coolant Cooler I wanted to have some type of baseline to compare test results to. In order to create this baseline I needed to test both Engine Coolant and Engine Oil Temperatures without the cooler installed.

I installed two of Kevin’s remote temperature sensors. One at the Engine coolant system gooseneck, and the other at the oil pressure-sending unit.

These sensors where connected to the ‘black box” computer system that poled each sensor three (3) times per second and recorded the temperatures into a database. Being these temperatures where recorded at exactly time intervals, the data collected was recorded over time. This enable the ability to see the “ramp up” or how fast or slow the coolant or oil reached operating temperatures.

Please note the entire test consisted of starting a stone cold engine and driving it from my home to the interstate highway, where I then continued to drive for 1 hour. The Black Box was set to begin to collect data once the temperatures reached just above 100 degrees F.

Engine RPM was kept at 2,200 as much as I possibly could.

Outside air temperature at the start of this test was 95.6 degrees F.

Baseline Testing
Here is a graph representing ALL the temperatures collected during a 30-minute period of time, (5,400 temperatures over 30 minutes for each.) prior to installing the cooler.

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The Red Line represents the temperatures, over time, of the Engine Coolant.

The Blue Line represents the temperatures, over time, of the Engine Oil.

What I find remarkable about this chart is that the engine Coolant ramps up to operating temperature much quicker then the engine oil does.

What does this mean to me, or how important is it?

I have no clue, but it is fairly obvious and therefore notable to me.

Highest Temps
The highest temperature recorded in the first 30 minutes for each, prior to installing the cooler are:

Oil = 268.8 F

Coolant = 202.9 F

After the first 30 minutes both the coolant and engine oil temperatures became very stable.

If I were to include them in this graph the variances would be so small you could not see them. (Read that; for the most part they would be a straight horizontal line.)

The Second 30 minutes of this test resulted in the following;

Oil Average Temperature = 250.4 F
Oil Highest Temperature = 273.2 F

Coolant Average Temperature = 204.7 F
Coolant Highest Temperature = 209.5 F

Oil Cooler Results

Here is a graph of the first 30-minutes using them same testing procedures as those used to create the baseline. (As close as I could make them the same.

Outside air temperatures at the start of this test were 97.4 F.

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Looks a little different don’t it?

Don’t worry I’m going to put the two graphs together so you can see the changes more clearly.

Seem to me like the oil temps are a lot more linear then they were before. Could the “Coolant Temps that raise quicker be transferring heat to the cooler oil for the first 25 minutes or so? Helping the oil get up to operating temperature quicker?

Here are the numbers after the Oil to Coolant Cooler was installed.

Highest Temps
The highest temperature recorded in the first 30 minutes for each, prior to installing the cooler are:

Oil = 237.6 F[u/] (This is 31.2 F cooler then the baseline)

Coolant = 202.0 F (This is 0.9 F cooler then the baseline?)

Once again after the first 30 minutes both the coolant and engine oil temperatures became very stable.

The Second 30 minutes of this test resulted in the following;

Oil Average Temperature = 236.1 F (This is 14.3 F Cooler then the baseline)
Oil Highest Temperature = 242.1 F (This is 31.1 F Cooler then the baseline)

Coolant Average Temperature = 207.4 F ( 2.7 F Warmer then the baseline)
[u]Coolant Highest Temperature = 209.8 F
( only 0.3 F Warmer then the baseline)

My Interpretation

My testing shows that he Oil to Coolant Cooler does a nice job of lowering the engine oil temperatures what looks like a bit more then 14 degrees F. at 236.1 degrees F it falls within the SAE idle oil temperature range of 210 to 240 degrees F.

Anything lower then 210 F will not allow water to be boiled off out of the oil.

Anything over 240 degrees cause the oil to allow higher level of wear.

The “cost” of doing this appears to be an additional 2.7 degrees F to the coolant temperatures. Give that’s within what I consider to be normal operating range I am comfortable with that.

Direct Comparison Graphs

For your reading pleasure.

Oil Graph

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Coolant Graph[/

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Additional Captured Info

I left the Temperature sensors installed on my Jeep for better then 6 weeks.

During this time the oil temperature never exceeded 244.2 degrees F.

The total average temperature of the oil during this time was 232.7 degrees F.

While I have the data for coolant temperatures during this period I have not analyzed it for highest or average. I will at some time. Right now all I can say is there were no problems that I am aware of with the coolant temperatures going outside a normal operating range. (I’ll get to this data shortly.)

Installation Pictures

This unit is installed on my 1997 Jeep TJ 4.0L. Testing was

The installation is straightforward. If you know how to remove and install your oil filter, you have just about all the skills you need.

Find your oil filter and remove it.

Note: Put a pan under it or you get a mess. Don’t laugh. For whatever reason when I installed this unit on my Jeep I didn’t put the pan under there before taking the filter off. (OK, ok, you can laugh, I deserve it!)

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Here’s a look from the bottom after you remove the oil filter.

The threads that the oil filter screws onto are the same threads the oil to Coolant Cooler will screw onto.

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Position the Oil to Coolant Cooler in place on the threads and slowly thread it into place. Once the gasket contacts the engine plate, position the Cooler where you want the hose nipples to point and then tighten down on the nut on the outside of the Cooler. This will compress the seal against the engine and set your hose position for you.

Here is what it looks like from the bottom.

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And here is what it looks like from the topside of the engine compartment.

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Then simply install the engine oil filter onto the cooler. Hand tight with another ¼ turn.

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All that is left to do is cut the heater return hose (11/16-inch) and attach each end to the top cooler nipples and refill your coolant and top off the engine oil level.

Sorry I ran out of digital memory camera card and don’t have pictures with the two hoses attached. I will get some though, even if basically boring!

Where to find an Oil to Coolant Cooler


These things are not common, but they aren’t rare if you know where to look for them.

In addition they come in different flavors and styles too.

The unit I installed came off of a 1989 Ford Crown Victoria Police Cruiser. In the 1980’s and early 1990’s these units where an option when the police cruisers where ordered by the factory.

The unit is made my Modine Manufacturing.

PLEASE NOTE: If you go salvage yard hunting you need to know these come in two thread sizes. You want a unit off the following Ford Engines. Small block 289, 302, 351C or 351W. Also off the old big blocks, 352, 390, 427 (yes Ford made one, it was a SOHC engine) or the 428 wedge.

On rare occasion you will find one of these on a 190 – 92 Ford Mustang.

And believe it or not, almost all the 4 cylinder Merkur (spelling?) have this unit installed.

The oil filter threads on all above engines are a perfect match to those on the Jeep 4.0 and 2.5L engines. (I will give exact thread size later. I don't have it in front of me right now.

[b]DO NOT get one off the new “Modular (read that metric, 4.6, 5.0 etc.) V8’s. They use the 22 mm filter thread and that will not fit the Jeep engine.

I have more info on other, different flavors of these oil to coolant coolers that I will post hopefully tomorrow. Along with similar coolers to handle the Power Steering Fluid temps too.

That’s it for tonight folks.

I will post this, see all my typo’s after I post it and spend half the night fixing them.

I hope some find this useful.


#2 User is offline   Jim B 

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  Posted 06 January 2004 - 10:06 AM


One of these days you and I are going to have to get together so I can take pictures of inside your hood. By now, can you actually get your hands in there to do any service work? :gossip:

As always excellent & detail write up and another tip & trick mod. :2thumup:
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#3 User is offline   jeepincj78 

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Posted 06 January 2004 - 07:22 PM

All I can say is WOW!!!!!!!!!!!!!!!!! And thank you for the wonderfull write up.

Frank :2thumup: :gossip:
1978 Jeep CJ7 4.0HO w/ Headmann Headers, MSD ignition, front dana 30 with Warn axle shafts, Warn premium locking hubs, custom drive shafts front and rear, NP 435 Transmission (6.69 to 1 first), dana 300 transfercase, model 20 rear differential with superior axles, Ox lockers front and rear, 4.10 gears, Currie twin stick, Warn premium front locking hubs, BDS 4" spring under suspension, Rancho RS 5000 shocks, revolver front shackles, warn XD9000I winch, 35" General Grabber M/T, Rubicon Express hand throttle and sway bar disconnects, dual optima batteries(red and yellow top) w/incab switch, and a on board hot water shower.

#4 User is offline   Daless2 

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Posted 07 January 2004 - 12:04 PM

Hi Folks,

I wanted to post a few more pictures of some other Oil to Coolant Coolers I managed to acquire during this effort.

Perhaps in seeing these it might help you in your hunt for similar items in the salvage yards.

Please note I have several extras of most of these coolers if anyone has an interest, PM me.

Other Oil Cooler Flavors

This unit is made by Longs Manufacturing Company for Ford Racing. It has the proper threads to fit the Jeep Engine, but is rather larger.

This is a cast, heavy-duty unit that plumbs into the lower radiator hose. This design has to cool the oil to a much greater degree then the unit I installed, as the coolant coming out of the bottom of the radiator is much cooler (about 168 degrees F) then the coolant in the heater core circuit. The casting has more then a few tap plugs in it for all types of measuring sensors. (temp, pressure, ECT.)

Here are two pictures. I think you can see how this unit bolts up to the block, and how the oil filter spins onto this unit.

The two large hose connectors are for the lower radiator hose.

The cooler heat exchanger is in the square looking box.

This is a straight bolt on to any of the Ford engines I listed in the original post, including the lower radiator hose connections. While I did not install this unit on my TJ I do believe it would work with a little effort, planning and perhaps some minor fitment fabricating.

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Yes it was dropped it right on the filter end! Who says Fram filters are not tough! LOL

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Here is a similar, yet smaller bolt on assembly, which is also available from Ford Racing. It too is made by Longs.

This is similar in design as to the unit above in that it plumbs into the lower radiator hose. The heat exchanger is far more compact

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This too is a straight bolt on to any of the Ford engines I listed in the original post, including the lower radiator hose connections. While I did not install this unit on my TJ I do believe it would work with a little effort, planning and perhaps some minor fitment fabricating.

Here is a picture of a brand new unit available from Ford that fits the Explorer with the new Modular V8. This unit WILL NOT fit the Jeep directly as the threads are 22 mm x 1.5

If you wanted this to work you would have to buy the thread adaptors from any of the remote oil filter manufactures to adapt this.

I am posting this picture in case someone wants to print it and go to the Ford Parts counter to buy a unit that will work on your Jeep. Just be sure you get a unit from one of the engines I listed in the original post and that the threads are ¾-inch x 16 tpi

While I do not know for sure I have been told these units are expensive from Ford. In the $150 to $200 price range.

Also, please note, you need three parts, the oil to coolant cooler, the threaded stud and the gasket that goes between the cool and the engine block.

Here is what it looks like.

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Please note, I do have this part number if anyone wants it, but again this will not directly bolt up to the Jeep engine because of the thread size difference.

Other New Oil to Coolant Cooler Sources

Welsh Racing sells a similar oil to coolant cooler with a twist.

There cooler ($180) threads onto the engine bock same as these. It also has two small heater core hose connections on it and you can use it that way.

However, they also offer a small Lower Radiator Hose “Tap In” so that you can pull the lower temperature coolant from the lower radiator hose to cool your oil.

They sell this Lower Radiator Hose “tap-in” for $51.

The web site is

I DO NOT know if the unit they are selling will be a straight bolt on to the Jeep Engine or not. If it has the ¾ x 16 threads it should work, but you need to check it out for yourself.

I would imagine because of the cooler coolant temperatures, this setup would reduce oil temperatures even farther. I just don’t know by how much.

Power Steering Coolers

In my hunt for these oil to coolant coolers I came across several rather unique Power Steering Coolers.

Please note I have not tested any of these units yet. I plan to install the Chevy unit sometimes next summer, but haven’t done so yet.

As I said I plan to do a little bit more testing on this and it’s value to my TJ in the future.

Here are some pictures and what I know about them.

Chevy Camaro with LS1 V8
This PS Cooler is inserted into the lower radiator hose and the low-pressure side of the power steering pump (The return line between the Steering Box and the PS Pump).

I think you can see the ends are connected inline with the lower radiator hose.

The picture is a bit dark, but you can see the two nipples on the top where the PS system plumbs into the unit.

This unit came off a 2001 Chevy Camaro with the LS1 V8 in it. If you salvage yard shop for this don’t bother looking for it in V6 Camaro’s. It would be there. Only the Aluminum block LS1 has this. (Based on my experience. I could be wrong.)

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Ford Crown Victoria

Here is a similar PS Cooler that can be found on any late model Ford Crown Vic. It too is inserted into the lower radiator hose.

There are two funky looking hoses attached to this unit that connect to the low pressure return line for the power steering pump.

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Oil Filter Thread Conversion Chart
In my travels I found this site, which lists the thread size of the oil filters for most vehicles and engines. Perhaps you will find it useful at some time.

Please Note, apparently all Toyota’s do indeed use a ¾-inch by 16 threads on their filters. I verified this. Some folks have shared they had similar oil to coolant coolers on their Toyota’s. While I have no experience in fitting a Toyota unit to the Jeep engine, I do feel confident to say the threads will fit. I do not know id the gasket-mating surface would be the same. (I do plan to find out.) Perhaps the Toyota truck line may turn out to be another source of these coolers.

Other Info

I have a bit more info on another oil cooler product that is very inexpensive and so easy to install it almost appear to be a gimmick. I will write it up and add it to this post a bit later. I want to answer some of the replie first.

Have a great day,


#5 User is offline   Daless2 

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Posted 07 January 2004 - 02:15 PM

Jim B, on Jan 6 2004, 10:06 AM, said:


One of these days you and I are going to have to get together so I can take pictures of inside your hood.  By now, can you actually get your hands in there to do any service work?  :gossip:

As always excellent & detail write up and another tip & trick mod.  :2thumup:

Hi Jim,

Thanks for your kind words, and yes I'd enjoy meeting up with you sometime. We have to make that happen this year.

On the Jeep....

Why do you think I have such a fixation with cooling???

My engine compartment is so stuffed even air can't get in there, let alone hands!

In truth I am about to start a removal process under the hood to make more room.

The engine is coming out so I can remove 0.030 off the cylinder walls and add a stroked crankshaft. This should make another 0.7L of space under the hood (so to speak!)

I haven't started the project yet, as I am waiting for the crank I sent out to come back from the machine shop. In the mean time I have tuned my engine up and have it scheduled for some horsepower and torque reading on a chassis dynamometer. Then I will do the same after I punch it out, stroke it, add a mild torquer cam, and port and polish the head.

Seams like another lifetime ago, but I use to do this stuff back in the early 60's with some pretty good results. I'm hoping I haven't lost my touch. If I have, no problem, I'll pull it all and drop in a 6.0L PowerStroke that I have! (That's the backup plan.)

I just love playing around with new things and learning new stuff along the way. Life is so good!

Have a great day,


#6 User is offline   Daless2 

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Posted 07 January 2004 - 11:16 PM

Hi Folks,

This is the last piece of info I have on my oil temperature tests.

Aluminum Oil Filter Cooler “Collar”

Have you ever seen those funky looking aluminum “collars” that slip on the oil filters?

The unit advertised as an Oil Cooler?

I have and I wanted to see how well, if any it workked.

Here is a picture of what I am talking about. I installed it on an oil filter on my shop bench.

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This is nothing more then a piece of extruded aluminum bent in a circle and held onto the outside of an oil filter with a large hose clamp.

A unit like this can be purchased from J.C. Whiney for about $19. It can also be purchased from Summit Racing and even Jeg’s for about the same price.

If you try one of these on a TJ with a 4.0L engine, be sure to put the collar on BEFORE you screw the filter in place on the block. There is just not enough clearance to get it on the filter once the filter is in place.

How Well does it Work?

I did more then a bit of testing with this as I wanted to see if there was any value to it. In truth I spent more time testing this thing then I did all the other testing efforts combined.

The first test I ran, I installed the collar on the filter and ran my 1-hour test as I described earlier in the post. To my surprise, the oil temps were higher. By 6 degrees F both in average oil temp and in the high oil temp recorded.

While I didn’t expect much I did expect to get some value out of my $19.

This was puzzling to me

I decided to take the filter out and take another look at the collar. When I slid it off the filter housing I noticed it scarped the paint off the filter “can” in three places.

So…. I slid it on and off a few more times taking notice, that even after the hose clamp was tightened down the aluminum collar only contacted the oil filter can in three places, at best.

I wanted to try something.

Using a new filter I covered the entire outside of the oil filter “can” with grease. Yes the same grease I use on my ball joints.

I then re-installed the collar on the oil filter, tightened down the clamp and installed the filter on the engine. After topping off the oil I retested for the same 1-hour test.

The grease folks made a world of difference.

Oil temps now dropped 4.7 degrees on average and the high oil temp dropped by 12 degrees.

I concluded from this test that the Grease is enabling a much better heat transfer from the oil filter “can” to the aluminum fins where it can then dissipates into the air.

I took this one step farther. I figured if I could improve the airflow around the oil filter with collar I could also improve the cooling effect.

I did this by removing the rubber like skirt from inside the passenger side fender.

This is the skirt that hangs down to cover the space between the fender and the Jeep frame.

I ran the one-hour test again and this time I recorded an oil temperature drop of 7.4 degrees F on average and a high temp recording that was down by 16 degrees F.

Bottom Line

I think for less then 20 bucks this is a worthwhile investment.

I particularly like that the engine oil never leaves the engine and therefore isn’t subject to a higher potential to leak.

If you go this way make sure you cover the oil filter on the outside with a nice coating of GREASE before you put the oil cooling “collar” on or I don’t think you will see any benefit to it.

I also would not recommend running around off road without that fender skirt in place. There is just too much opportunity for a rock to find the thin metal on the cap of the oil filter and put a nice hole in it.

I think a better solution would be one of those small 12-volt 4-inch pancake fans to blow air on the collar, however I did not test how well that would work.

If I did not have the oil to coolant cooler in place I would use this $19 cooler the way I have tested. That said, please know you can’t use both at the same time.

You just don’t have the clearance on the TJ with 4.0L to get the filter with collar on it, onto the end of the oil to coolant cooler.

I hope some find this helpful,


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