# 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part

Commonly used on Cummins 5.9L ISB/QSB.

3975986 Cummins Transmission Cooler 3" X 9" OAL bundle Diameter Oil Cooler CuNi. 3975986 and 3975986CN are the same part, both with a Copper Nickel bundle.

Core length = 6", overall length = 9.5" (tail to tail)

This cooler has 1.3/4" water fittings.

This is a Mr Cool (USA) part MRC3975986CN

**Cooler Measurements:**

-   3-1/8" Outside diameter
-   10-3/4" Overall Lenth
-   ½" NPT Oil Connections
-   1-3/4" Water Connections
-   1/8" NPT Drain port (4 Different Locations)

**Our product is a drop in replacement for these part numbers:**

-   Cummins® :
-     
    
-   3975986
-   3975986CN
-   3972979
-   3972979CN

**This part fits the following engines (possibly more):**

-   QSB5.9L
-   QSB6.7L
-   QSB5.9 CM850
-   QSB6.7L CM2250

This is a Mr Cool (USA) marine part MRC3975986CN

## Details

- **Price:** 1028.5 AUD
- **Vendor:** Mr Cool
- **Tags:** Sawley’s AAM Aftermarket – Cooling Systems Mr Cool | Marine Heat Exchangers & Kits

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 1028.50 AUD | In stock |

## Images

- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part
- 3975986CN Cummins 5.9L ISB/QSB Oil Cooler 3"x 9" 3975986CN 1.3/4'' Replacement Part

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> Source: [Sawley's Auto and Marine](https://www.sawleysautoandmarine.com.au/products/3975986cn-cummins-5-9l-isb-qsb-oil-cooler-3x-9-3975986cn-1-3-4-replacement-part)
> Updated: 2026-06-23