Oil cooler piping, 1999 GMC Jimmy.
Fixing An Oil Leak:

Replacing Oil Cooler Lines In A
1999 GMC Jimmy or Chevy Blazer

May Also Apply To Chevy S10 And GMC Sonoma


In This Article:

Retaining rings are removed and the oil lines disconnected from the radiator. The lower end is unbolted from the remote oil filter housing. New oil cooler lines are installed with new retaining rings.

Related Articles:

Skill Level: 3 (Intermediate) Time Taken: About 2 Hours

By Bruce W. Maki, Editor


Some GMC Jimmys and Chevy Blazers have an engine oil cooler. Similar to a transmission fluid cooler, the oil cooler is actually placed inside the radiator, with metal/rubber lines that carry the pressurized engine oil to and from the oil filter. Furthermore, the Blazer/Jimmy has a remote oil filter. I guess GM did this because the 4.3 liter V6 engine fits so tight there was no room for an oil filter mounted to the engine block.

The 1999 Jimmy in this article had been leaking oil for several years. When a mechanic is asked to fix an oil leak, he (or she) will normally degrease the engine first. Finding the source of an oil leak is much easier wihen the engine is clean.

But the oil wasn't leaking from the engine. There was a large wet oily spot just behind the radiator, on the driver's side.

I did this repair while I had the car in my garage to replace the water pump. This task was easier with the radiator fan and fan shroud removed, but it should be possible with those things left in place.


Before starting all these repairs I removed the plastic splash guard that extends from the front bumper to the front axle area. There were 6 bolts to take out.

The Oil Cooler Lines:

  • Arrow "A" points to the upper oil cooler connection that needed to be removed.
  • Arrow "B" is the lower connection.
  • The red circle indicates the location of the oil filter. The lower end of the oil cooler lines connect here, but are not visible in this photo.

This entire area was covered with oil and dirt. I suppose I could've taken a "before" picture, but all you would see is a big black shiny mass of sticky oily dirty goo.

I spent at least an hour cleaning off the oil/dirt mixture from the area around the black rubber hoses (just to the left of the letter "B")

Oil cooler line location.


Oil cooler line, possible leak point.

A Closer View:

The red arrow points to the suspected leak location. The metal tube looked bumpy and corroded in this area. This was about the highest part of the wet spot, and the oil had been blown toward the rear and also towards the center of the vehicle.

I could have completed my other repairs and then run the engine to verify the leak source, but that would involve much more work.

When I called my local NAPA store and found that a set of oil cooler lines cost only $30, I took a chance that replacing this part would fix the oil leak.


Cleaning The Oily Mess:

Since this had been leaking for several years, the oil had thickened into a tar-like substance with dirt mixed in.

I did this repair in February, in northern Michigan. If I had done this repair in the summer months, I would have used an ordinary engine degreaser product that can be washed off with a garden hose. It might have required several cans of degreaser.

Since I couldn't use a garden hose, I employed some all-solvent methods:

  • I had a plastic WD-40 spray bottle that can be refilled. I figured the sprayer could tolerate solvents, so I poured out the WD-40 and put mineral spirits (paint thinner) in the bottle. I sprayed the oily mess with mineral spirits and brushed everything with an ordinary parts-cleaning brush. I sprayed and brushed repeatedly.
  • I put a dishpan underneath the car to catch the solvent run-off.
  • After most of the grime was cleaned up, I sprayed the area with brake parts cleaner, which is a volatile solvent that removes oil and grease. This required serious ventilation, so I opened all the doors.

Why not start cleaning with brake cleaner? Brake cleaner evaporates to fast and won't stay around long enough to soften the thick oil and tar-like stuff. Mineral spirits is much less volatile. Since it doesn't evaporate rapidly it will disolve thick materials, such as tar.

Alternatives To Mineral Spirits:

  • WD-40 will also dissolve motor oil and grease... it's just more expensive than mineral spirits, and it leaves a light oily film behind.
  • A chemist once told me that charcoal lighter fluid is the same as odorless mineral spirits. I sometimes use charcoal starter instead of paint thinner.

BE CAREFUL: All of these solvents are flammable, doubly so when they are sprayed. DO NOT use solvents around an open flame or any ignition source, such as a cigarette or hot engine.


Removing The Oil Lines From The Radiator:

Since I already had the cooling system drained for other repairs, I removed the upper radiator hose for easier access.

The oil cooler lines are connected to the radiator by a simple snap ring (red arrow).

I used a small screwdriver to push on the end of the snap ring and remove it.

Removing retaining ring, oil cooler line, GMC.


Oil cooler tube, retaining ring slots. The snap ring goes into a set of 3 rectangular slots (arrow).


Upper Oil Cooler Connection:

I used two small pry bars to carefully push the tube away from the radiator, using a twisting action to separate the parts.

I was careful to avoid prying near the slots because I figured the metal could break easily, and then I'd need to replace the adapter fitting.

Prying oil cooler tube away from radiator.


Oil cooler upper tube, after disconnecting.

As soon as I opened this connection, oil started dripping from the oil filter housing, so I put a catch basin under it.

In hindsight, the upper tube would be easier to remove if it was rotated back-and-forth before using the pry bars. But... that might be difficult while the other end of the cooler lines are still attached to the oil filter housing. So maybe removing the lower connection first is the better approach.


The lower oil line connection was very tight, so I used a 7/8 inch wrench to wiggle the fitting back-and-forth. While there are wrench flats on the ends of these tubes, they are NOT nuts that rotate. I guess the wrench flats are just for wiggling the tubes to break them free.

After loosening the connection with the wrench, I just wiggled the pipe by hand while pulling, and it came right out. Maybe prying isn't such a good method.

Removing lower oil cooler line, 99 Jimmy.


Remote oil filter, oil cooler connection, GMC.

This is the remote oil filter, viewed from the passenger side of the car. This thing is directly behind the bumper, just left of center.

The oil cooler lines are indicated with red arrows. The lines to the left of the filter housing go to the engine.


Another view of the oil filter housing (seen through the opening in the front bumper). Using a 13mm socket, I removed the bolt that held the lines to the filter housing.

This bolt was REALLY tight.

Remote oil filter, 1999 GMC Jimmy.


Prying oil cooler lines from filter housing.

I pried on the metal block, right between the two pipes, and the oil lines separated from the filter housing.

More oil dripped from here, so I had a dishpan underneath.


The new and old oil cooler lines.

The new part was a little different from the original. The tubing stuck out farther at the radiator connections.

New and old oil cooler line assemblies.


Filter end of oil cooler lines. The new part has slightly different connections.


The original part didn't have the built-in gasket.


Gaskets on oil filter housing.

The original gaskets (red arrows) stayed on the filter housing.

I carefully pried these off and sprayed the area with brake cleaner to remove the oil.

Then again, maybe it doesn't hurt to have some oil on the mating surfaces.


I installed the lower end of the oil cooler lines, but this time I had to use a deep socket because the tubing has a different design.

I tightened this bolt pretty hard, but I was leery of stripping the threads in the aluminum block of the oil filter housing.

Installing lower end of oil cooler line, 99 Jimmy.


Oil cooler pipe retaining rings.

The new oil lines came with new retaining clips, which are the blue ones.

The instructions say "Do not reuse the original retaining clips".


To get the new retaining clip into place properly, I placed one end into a slot and then used a small screwdriver to lift the other end over the "hump". Installing retaining ring clip in radiator, oil cooler lines.


Ears visible on retaining ring.

The 3 "ears" of the retaining clip each need to engaged in a slot, so the ears are visible when you look straight into the hole.

You can barely see the third ear, just left of top-center.


I left the protective caps on the ends until I was ready to insert the tubes into the radiator.


New oil cooler line being pushed into radiator connection. I dabbed a little oil on the ends of the tubes before inserting them into the fittings. Can't hurt, might help.


I pushed the oil line into the radiator fitting until it made a "click" sound.

I'm not sure what this black plastic ring is for...


...but it fits over the end of the fitting.

I guess it keeps that blue retaining ring from falling out.


The completed oil line installation.

The arrows indicate the new oil lines.



The plastic air filter box rubbed against the top oil cooler line, because the tube had a different way of making that right-angle turn.


So I wrapped the tubing with electrical tape where it touched the air filter box.

The purpose of the tape is to highlight how much abrasion is occurring here. I'll look at this in a few months to see how badly chewed up the tape looks. I may need to squeeze a piece of foam between the tube and the air filter box to prevent the tube from developing a leak.


Cleaning oil-covered parts in a plastic storage tote.

Cleaning The Splash Guard:

The plastic splash guard had a lot of oil and dirt on it. I placed the splash guard in a large Sterilite tote bin and poured about a cup of miineral spirits in the bottom. Then I dipped the parts cleaning brush in solvent and brushed all the oil/dirt until it I could see bare plastic. After I wiped off the solvent with a paper towel, I sprayed the splash guard with brake cleaner and let it dry before putting it back on the car.


After I put the car back together, I installed the oil filter, replaced the oil drain plug, and put the usual 4-1/2 quarts of oil in the engine. Then I ran the engine and checked for leaks.

When I checked the oil level, it was about 1/2 quart low. That didn't surprise me, given how much oil spilled out of the oil cooler lines. That also explains why whenever I've changed the oil in this car, the oil looks dirty right away. There is a half-quart of old oil in the oil cooler lines that doesn't drain out. Next time I change the oil I think I'll try blowing compressed air into the oil filter center connection. Maybe it will purge the oil cooler lines. I'll let y'all know.


Getting Rid Of Old Dirty Mineral Spirits:

Properly disposing of used solvent isn't simple. I just pour the mineral spirits back into an empty paint thinner jug and label it as "used". In my area, the county runs a hazardous waste disposal program where homeowners can drop off stuff like used paint thinner. Also, if I'm having a bonfire, I'll pour a little used paint thinner on the firewood before igniting it. After all, this is basically barbeque starter.


More Info:

Tools Used:

  • Sockets: 13mm
  • Wrenches: 7/8"
  • Small Pry Bar
  • Needle-nose Pliers
  • Small Flat Screwdriver
  • Parts Cleaning Brush
  • Dishpan
  • Large Plastic Tote Bin (for cleaning parts)

Materials Used:

  • Oil Cooler Lines, NAPA Part No. 823-2231, (About $30)
  • Mineral Spirits
  • Brake Parts Cleaner

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Written March 6, 2008