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Update - Photos: I took some photos this morning in the daylight. I'm not sure if the liquid on the ground was from my MJ or something else. Hard to say. But it definitely looks to me like I'm getting some leakage around the base of the radiator. I've pasted them at the bottom of this post. I snapped these real quick on my way out to work. Will take a closer look after I get off. Some Background: If you have time, please read the whole post for all the details and then see my questions at the end. It took a while, but I finally got new tires on my MJ. I'd been driving on very old tires for way too long, and I was pretty sure they were causing the truck to shake at highway speeds. After getting the new tires installed (Good Year DuraTracs - 235/75/15), I was stoked to find that they significantly improved my drive on the freeway, and I drove about 30-40 miles at normal highway speeds for the first time in a long time. It felt great to be able to do that again, and I hope that I may finally be close to resolving my long battle with death wobble and not-so-deadly shimming. (If you've followed other posts of mine, you may remember that I had a lot of work done on the Jeep to fix the death wobble and that I'd made a lot of progress, but still needed to replace the tires). Anyway, that's not really what this post is about. The Overheating Issue: When I got off the freeway, I noticed that my heat gauge was redlining, so I pulled over. I popped the hood and saw that the coolant reservoir was boiling and that the cap on the reservoir is cracked. I let the truck cool off for a few hours and then drove back home (another 40 miles or so). It was probably around 80 degrees when I started driving earlier. By the time I drove home, it was night time and it was much cooler outside. I turned on the heat in the cab and made it all the way back home without any overheating issues or boiling (at least none that I could hear... I did not pop the hood when I got home, I just listened to see if I could hear any gurgling). My Theories So Far: The crack in the coolant reservoir cap concerns me, but I actually think that's been there for a long time. I have a 1987 2.5L, and my Haynes manual says that the overflow reservoir in these is not part of a pressurized system. But I'm no expert on this front. I have to do some more troubleshooting, but my first thought is that the water pump might be dying. The only other time I've encountered the boiling reservoir it was when my first water pump was shot. I replaced it probably 4 years ago now. Right before I noticed the overheating, I heard some engine noise that sounded similar to what it sounded like the last time the water pump went out. It was kinda like the sound of clanking metal being carried into the cab via tubes. It's not as pronounced as it was when I last changed the pump, but it definitely sounded similar. My Questions: Do you all think my water pump is going bad again? Do you think that's a good, low cost place to start? I drive the truck a fair amount, but it is not what I'd call a daily driver either. I have taken it on some pretty bumpy roads though since replacing the water pump and gone on some long road trips... so there's that. How vital is it to get a new reservoir cap for a 1987 2.5L? I definitely am planning to fix that ASAP, since it will be pretty cheap and I think relatively easy. Not trying to avoid it. Just wondering what my priorities should be. Is there any chance you think having the tires changed could have resulted in knocking something loose or shifting some fluid around or something? Like I said, this isn't exactly a daily driver, but I have made the trip I made today plenty of times over the past few years and sometimes on much hotter days. I wouldn't think the shop could have caused this, but I just am trying to understand why this happened today. I'm also wondering if driving it over 70 mph for the first time in a long time is why this cropped up today. Maybe the water pump has been going for a while and I just haven't pushed the truck hard enough in a while. Maybe the installation of power steering and new belts helped speed this problem along? When I got it worked on for Death Wobble, I also had power steering put in. And ever since then, there has been what I have assumed was belt noise. I tried a few simple things to resolve it, like tightening the belts, but I didn't ever get to the bottom of what was causing the noise. It wasn't a tell-tale screeching, but the noise would temporarily go away when I sprayed soapy water on the running belts, which made me think it was the belt. But maybe the soap was also lubing up the bearings in the water pump housing and thus stopping the noise temporarily? Finally, on a side note and in relation to the Death Wobble: How much jiggle is normal on a healthy MJ when driving on the freeway? I drove my truck for way too long with it's wobble issues before all the fixes (which I outlined in this comment). Now I'm a bit traumatized and I can't really remember what it was like before the wobble started presenting itself. I'm hoping that I start to get my trust back with time. Driving the truck today, after getting the new tires on, it felt soooo much better, but it still shakes when I hit a bump. I mean, obviously a 38 year old truck is going to shake when it hits a bump in the road, but I'm left wondering what is normal and what isn't... --- --- --- OK. I hope some of you will read this and respond to my questions. As always, any and all insights are appreciated, so thanks in advance!

87 Renix 4.0, closed system. My engine was rebuilt last year and has only a few thousand mile so far. I believe all small parts were replaced. On Friday, I loaded up the MJ for a weekend camp trip. Nothing heavy, just tent, sleeping bags, cooler, etc. and a passenger. This is probably the most weight it has carried since the rebuild. The outside temp was mild - 70s. I started out and looked down at the cluster. The temp gauge usually stops at the first line. Very seldom does it rise above this. Well, I was watching it continue past that and go above 210. I had only driven 3 miles. Then the temp dropped down to "normal," just above the first line. I stopped at a McD's for coffee. I looked under the hood and noticed antifreeze around the reservoir bottle. The cap was loose and would no longer screw down tight. i turned back and tranferred all my gear into a Suburban. I have ordered a new cap from NAPA. For the big question: Should I replace the T-stat also? What may have caused the sudden, rapid rise, and rapid drop?