Tube Nest, or "O"- ring sealed coolers

The tube nest, or O-ring sealed, oil cooler was once a very common design used by many OEMs including Fiat-Allis/ Allis -Chalmers, Terex / Detroit Diesel, Cummins, Mack and many other smaller, specialty OEMs.

The design withstood a decent amount of vibration, was relatively inexpensive and easy to replace. Tube bundle oil coolers have a "lip" around the circumference of the cooler. This lip is usually either 1/2" or 3/4" tall and on either or both ends of the cooler, depending on the specific design. The purpose of this lip is to provide an area in with which the oil cooler and the O-ring seat.

The basic idea is the tube nest cooler is inserted into a housing. The housing has a groove in which sits an O-ring. The O-ring is placed in the housing before the oil cooler is inserted. The pressure between the O-ring and the housing and the oil cooler is what "seals" the unit and prevent the oil and coolant from mixing.

tube nest or O-ring sealed oil coolers

Recently, most of the OEMs have discontinued the O-ring sealed design. This has left many with the choice of having to try to find a used replacement or scrapping a good, working piece of equipment which costs $20, $30 even $50,000 to replace, just because the oil cooler is leaking and they cant find a replacement.

tube nest

PosiTech will custom make a new replacement oil cooler for any tube nest for which an OEM replacement is not available. We will machine headers to the exact size and build a replacement unit which is the exact configuration as the original.

Since all the sealing of the unit is between the O-ring and the header, making sure you have the exact same OD header as the original is critical. Most O-ring sealed units have a relatively tight tolerance. Too big, and the unit may not fir o may rip the O-ring during installation. Too small and the unit will not seal, and the unit will leak- either at the initial testing, or worst, after its been on the equipment for some time and thereby contaminating the oil.

At PosiTech we have decades of experience in matching up the proper header material, as well as how to make sure the OD is correct after running the header to tube joints. We can make any OD and length of tube nest you need.

Other than the OD of the header, number of baffles and length of the unit, there are a number of different types of tube nest coolers designs. In our catalog you will find some of the following examples:

1.  One O-ring seal on both ends.

This is by far the most common Allis-Chalmers replacement oil cooler, hydraulic cooler, engine oil cooler, torque converterdesign of tube nest. An example would be our PC 1207 replacement for the Allis-Chalmers or our 1401 and 1402 replacements for Terex / Detroit Diesel applications.

You can use the following links to straight there in our catalog, or use the Catalog tab, by OEM to look up further options, like our 1406, 1407, 1408 and more:


1401 and 1402:  or


2.   Double O-ring sealed.

Both the single seal and double seal were used by Cummins. An Cummins transmission oil cooler, engine oil cooler, hrdraulic cooler and torque converter coolerexample of the single seal can be seen on our PC 1602, 1603 o 1609  page, or by going to the links below, or using the catalog tab above and searching by OEM, "Cummins".

1602, 1603 and 1609: or or

The double sealed can be seen to the right as our PC1605 or at the link below:


3.   O-ring sealed one side.

The third style of O-ring sealed units is the O-ring sealed on Mack transmission oil cooler, charge air cooler, engine oil cooler, hrdraulic cooler and torque converter coolerone end, and gasket sealed on the other. An example of this can be seen to the right for our PC 1802 for Mack 6 cylinder engines.

Again, you can use the catalog scroll, search function or the link below to access more information.


Notice on this design that the bottom header has a plate. The top side of this cooler is inserted into the housing and seals at the O-ring like the above examples. The difference is the bottom pate sits flush against the housing and is sealed with  gasket, not an O-ring.


For each of the above, if you want to see the housings these would seat in, please search the catalog. These are only examples, we have other tube nest coolers in our catalog.

If you don't see a unit in our catalog matches up to your application, we will custom make any tube nest cooler for you. Please call and we will be happy to help.