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How to replace the thermostat on a Jeep Cherokee

How to replace the thermostat on a Jeep Cherokee

The thermostat controls the engine temperature in the Jeep Cherokee. It is located at the front of the cylinder head inside the water outlet. The thermostat limits coolant flow until the engine reaches 195 degrees F. With the thermostat open, coolant is free to flow to the radiator to be cooled. The thermostat opens and closes to regulate the flow and maintain the proper operating temperature for the engine.

Automotive thermostats consist of a wax pellet that melts at a predetermined temperature. As the wax melts, it opens the valve in the thermostat. As the valve ages, it can become partially stuck in either the open or closed position. Also, so thermostats have a latching mechanism that prevents the thermostat from ever closing again if it exceeds a certain temperature such as in an overheating episode.

To change the thermostat, you must remove the water outlet from the cylinder head. The outlet is held in place by two bolts. The upper bolt is easy to access. However, the drive belt blocks the lower bolt.

While it is possible to work around the belt, it is usually easier and less frustration to loosen the belt and move it out of the way. It is especially hard to get the bottom bolt started into the hole correctly with he belt in place.

When the system is opened, coolant will be lost. Either park the Jeep where the coolant can be collected or drain the radiator by removing the lower radiator hose. Either way is messy, so be prepared. Remember that anti freeze is toxic to pets and wildlife.

Remove the two hoses from the water outlet. Remove the two bolts. Gently pry the water outlet off. More coolant will likely come out at this point. The thermostat will likely stay in the head. Gently pop it loose.

Clean the mating surfaces of any old gasket material and corrosion. Attach the new gasket to the water outlet. If the new gasket does not have an adhesive use something like Permatex to attach it to the outlet piece. Install the new thermostat in the recess in the head. It should stay put. If it does not, try a spot of gasket sealer to hold it in place. If it slips out of the groove while installing the water outlet, it will cause a leak.

Place the water outlet over the new thermostat and install both bolts. Tighten them evenly. If you loosed the belt, tighten it now.

Leave the water hoses off and add coolant until it comes out the heater hose connection. Install the heater hose. Continue to add coolant until it comes out the larger connection. Install that hose. Continue to add coolant to fill the system.

There will likely still be some air in the system. Either remove the temperature sensor at the back of the head to bleed the air or heat cycle the engine a couple of time to purge the air.

Check for leaks. Test-drive the Jeep to make sure the new thermostat controls at the correct temperature. If the engine has been running too hot or too cold due to a bad thermostat, the computer may take time to adjust. There may also be other damage that caused overheating such as a leaking head gasket. The Jeep 4.0 engine is pretty tough and can survive some overheating. Recheck the coolant level again after the engine cools off.

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A Funny Yoke

A long while back, I ordered a yoke for a Chrysler 8.25 and the one they sent me did not fit. They promptly sent a replacement that did fit. They promised to send UPS to pick up the old one, but after a while, I forgot about it when the delivery driver never asked for it. So for a couple of years now it has been taking up space under a shelf somewhere.

Today I remembered that the sticker I found under the part number of the ill fitting yoke matched the later style 8.25. I had discovered that the later yoke had enough material on it to drill and add U bolts. So, I figured if I could find the funny yoke, I might work with it.

I little searching turned it up covered in spider webs. I also found Jennifer’s long lost hair dryer as well.

So I sat the yoke on a Chrysler 8.25 pinion and found that, after two years sitting in a box, it still did not fit. I double checked and sure enough the pinion for the early and late 8.25 rear is the same.

I counted the splines on both yokes and they were the same. I measured the inside diameter however and found the funny yoke to be a few thousandths smaller. That is when I noticed something I had not noticed before: it is drilled for U bolts, not tapped for straps. Cool. Now what does it fit?

It looked like a D 35 yoke so I tried it on a D 35 pinion. It mostly fit but it seemed the wrong depth.

Next, I dug around and found a D 30 pinion. Perfect fit! I did not have a D 30 seal to test the OD on but I am guessing it is a Dana 30 U bolt yoke.

So Jenny’s XJ will likely get a U bolt yoke when I install her 4.10 gears. I just have to confirm the OD.

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Fabricating a Bumper for a Jeep Cherokee XJ

Fabricating a Bumper for a Jeep Cherokee XJ

The bumper on my off Road Jeep is very simple. It consists of a couple of pieces of angle that extend the unibody frame rails out. The winch plate is mounted on top of them. There are a couple of pieces of curved pipe extending to each side to protect the bottom of the head light surround.

Since Jenny drives her Jeep everywhere she goes, she wanted something that was both functional and nice looking. Had I been fabricating form scratch, I would have used a piece of 2×6 tubing and tapered the ends to make a nice looking bumper. However, the cost of a stick of steel was out of budget for the moment.

What I had to work with was a damaged bumper on a parts Jeep sitting in the grass by the barn. It was made from heavy steel it was just not exactly the shape I wanted. It also had a brush guard and winch plate integrated into the design. Jenny did not want the brush guard and does not have a winch.

I began by removing the bumper from the parts XJ. There was an extra bolt that simply would not come loose. I had to cut it with a torch to get it out.

I began by cutting off the brush guard and its mounting brackets. Next I cut out the winch plate. This left a big gaping hole in the center of the bumper. I cut a couple pieces of angle and used those to fill in the gap.

I did not like the way the bumper stuck out from the front of the Jeep, so I relocated the mounting holes to pull it in closer to the grill. I would have liked to have tapered the ends but that would have meant extensive reworking of the bumper. By setting it back, the tips don’t really stick out too far.

I painted the bumper flat black to mask some of the weld marks and to match her rear bumper. I trimmed the ends of her rear bumper to be similar to the cut of the front bumper.

I removed her twisted stock bumper and the stock air dam.

Mounting the bumper to her Jeep Cherokee, required trimming the front fenders since part of the bumper extends back under the grill. I used a straight edge and a sharpie to make a mark on the fender. I used a cut off wheel in my grinder to make the cut. I touched up the raw edge with spray paint.

I tied the vacuum bottle to one of the fender supports with wire for now. I will move it inside the engine compartment later as the cut of the bumper leaves it venerable to breakage where it is.

The new bumper gives her Jeep a muck more aggressive look. It also improves her approach angle for off road obstacles compared to the stock bumper.