Diagnosing Engine Overheating

[NickyV]

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!

 

 

[AnotherOldJeepGuy]

My expertise is way less than the real experts here, but I can start the conversation with my related experience.

 

The last time my truck was overheating it was because there was air in the system.  I believe it got in there when work was down earlier, a new water pump, and the system was not sufficiently burped.  The air was worked out by letting it run with the reservoir cap off and adding fluid when it flowed and got low.  After that air was replaced with coolant, it no longer overheated.

 

If it were me I would go ahead and replace the cap.  [A side note here, to a degree (pun intended), is that my current overflow tank has swelled, I assume during the time the truck was over heating.  I mention this because a result of that swelling the cap, which has a relieve valve in to top of the cap, makes contact with the inside of the hood when closed just enough that I suspect it causes it to leak a tiny bit.  So, if you get a new cap, which could be taller than the original, and you notice a small amount of fluid at the cap, check to see if it is contacting the inside of the hood.  This tiny leak, for me, is not enough to cause a problem other than the need to add a little fluid from time to time.]

 

I recently had intermittent belt squeaking.  I could tell the belt was loose just by pressing on it to check the play.  And in my case as well a small squirt of water temporarily silenced the squeal.  I tightened the belt and the squeaking got worse!  Then I loosen it about half of what I had tightened and it became happy and stopped squeaking.  I later read, most likely here somewhere, a recommendation to "just tighten enough for the squeak to stop" which is probably where it ended up once I over tightened and then backed off a bit.

 

 

[89 MJ]

You are correct, the 2.5L coolant reservoir is not pressurized. Because it isn’t pressurized, I wouldn’t say replacing the cap is top priority, but should get done sometime soon. 
 

I could see the water pump going bad. They typically leak out of the weep hole when this happens, but not always. You could also try grabbing the fan and wiggling it or rocking it forward and back to see if the bearings in the pump are junk. If it’s making noise, it sounds to me like it’s no good though. While you’re replacing that, might want to look at doing a coolant flush and using a rust removal product inside the block to make sure that’s all clean along with the installation of a new water pump. Similarly, the radiator could be getting plugged up. 
 

There is a slight chance that the addition of power steering contributed, but there is an underlying issue if adding power steering caused it. The addition of the power steering pump is making the engine work slightly harder. 
 

In a stock truck or even a slightly modified truck, you should be able to let go of the wheel at 80 mph regardless of bumps and not have any shimmy in the wheel. 

[NickyV]

Thanks to both @AnotherOldJeepGuy and @89 MJ for the advice and hope to get more. It all makes sense.

 

I took a break from working on the truck for the past few months as it's been raining pretty frequently and I've been busy with other projects, but hope to get back into it soon. I'll try to do another post on the water pump and other fixes that I end up making.

 

Keep on truckin!

[pizzaman09]

Beyond checking the water pump, also check the harmonic balancer condition.  It is possible for the outer pulley to slip on the rubber layer and not actually transmit enough torque to run the pump, alternator and power steering.  It might not look bad but usually it will look like rubber extruding out the sides.