OVERHEATING diagnosis procedure?

I'd been noticing the electric fan coming on a lot recently - just while doing local errands. Perhaps I should have looked into it a bit deeper first since I knew there must have been a problem somewhere but I hoped it would somehow go away... just on the weekend I did a run up to joshua tree from los angeles and though I did notice the fan coming on things were generally okay. It probably doesn't help at ALL that I haven't had a temp gauge in the vehicle since I swapped in a 98 HO engine which has a totally incompatible to temp sending unit with my cluster gauge (it's been 14 years!! since the swap but I managed without it all this time)

So anyway - yesterday I'm doing a run on the freeway up to santa barbara (about 80-100 miles?) and after the first 30 miles suddenly i'm smelling coolant (though the girlfriend can't smell it so I'm not sure...) then I'm starting to notice a clacking sound for close to a minute so I let off the throttle and start coasting to a nearby offramp - but weirdly (after throwing it in neutral) i'm revving at 4000RPM and now even dropping into second gear will reduce it (weird huh???) so I just kill the motor and coast down the offramp exit. LUCKILY- there's a Shell station right around the corner - but I can't get it started again and so we push it into the lot of the gas station. There's smoke coming from the block (not sure if it's oil or water but seems to be water/steam) and coolant dripping everywhere below the block but I couldn't ascertain where it was coming from exactly. After cooling down it started find and the engine sounded pretty okay (and no revving etc - i assume maybe the overheating somehow made the throttle cable do something funny?)

In my experience this doesn't really happen as the result of a leaky hose etc... and i can only imagine maybe the t-stat or rad somehow got obstructed or blocked but I'm only going on what I imagine. So i'm wondering if there's a way I can kind of diagnose the problem before I start pulling the water pump etc (?) - I saw another post while trying to figure this out that mentioned checking spark plugs to see if there's a coolant leak INSIDE the block - so that seems like a great little forensic idea... if anyone has any more nuggets of wisdom along these lines and wouldn't mind sharing - I'd be eternally grateful... thanks!

Jonathan

92 XJ sport AX-15 5 speed with 98 HO, borla header, all the usual 'normal' equipment associated. (ps - the new engine has MAYBE 100K on it at most - though I should also mention i overheated it once before - badly and had to get the head rehoned and decked since it warped a wee bit)

Check to see if any of the freeze plugs are leaking on the driver side of the block. As for as not starting right away and having to let it sit.. the heat caused from overheating could have caused the fuel in the rail to vaporize ( vapor lock).

so was it ok the rest of the trip or is it still parked?
get a cooling system pressure tester, thats the first step to finding a leak. also fix your temp gauge or get a cheap aftermarket guage.

No i had to get towed back home.. didn't want to lose the whole engine. Thank god for triple-A! Thanasi - well seems there's little point in looking where the steam or coolant blew from.. There are no leaks during 'normal operation'... so there would be little point in checking the freeze plugs. Maybe I gave too much detail? Just trying to figure out a 'smart' way to go about figuring out why the coolant isn't circulating.

are you sure it isn't circulating? lots of things will contribute to over-heating, an obstruction isnt generally the problem.
it could be as simple as low coolant finally catching up with you. check the level and quality of your oil. a cracked head can rob you of coolant and not leave a puddle on the ground to notice.
start as simple as belt tension.. if it is slipping you will build up heat.
at highway speed with a good system you dont even need the fans to keep the temp down, so for some reason the heat build up by driving wasnt being disipated.
start it and let it get to temp at idle and see what happens. a leak may present itself once the system builds pressure.

Are you saying that you have gone 14 years w/o having to do anything to your cooling system?

I can't imagine operating a motor vehicle w/o a temp gauge but, as always, to each his own. A bit late now, but there are fairly simple ways to mount a sending unit for your '92 gauge cluster. There are threads on this.

You can check freeze plugs and spark plugs, etc. but your leak is likely to be outside the block. When a leak or overflow occurs while moving, the coolant blows back onto the block making it difficult to see where it is coming from. There is no magic here--you or a helper has to find the leak in the radiator or one of the hoses. I recently had a tiny pinhole leak in the front bend of one of my heater hoses that blew coolant everywhere.

It is also doubtful that the coolant caused your throttle cable to jam.

What do you mean by "normal operation"?

You may not even have any vanes left on the water pump.

If it has really been 14 years, I would just go ahead and replace everything but that's just me.

Thermostat might be stuck closed.. You look into that already?

Thanks for the ideas thus far. I appreciate it. The problem is not a leak. THe problem is 'why isn't my cooling system keeping the engine cool?' Question: what's the worst that can happen if i pull the t-stat? Slow warm up?

Thanasi - yes - I'm assuming the t-stat is/was the most likely culprit - but now I'm wondering about just ditching the t-stat altogether to get better coolant flow. Maybe it's no big deal if the engine doesn't get hot faster? what's two minutes to operating temp vs. 15...? I wonder....

Pelican - NO not at ALL. The last time I put in a new water pump was probably two years back... but it's only got MAYBE a few thousand miles on it since the last t-stat and water pump. It's been through about 4 water pumps in 14 years if memory serves. I would LOVE to have a temp gauge but just tapping a one inch hole into the block where I ASSUME it will be solid metal seems like a great way to play russian roulette with your engine. I've posted on here before asking for 98 HO engineering/casting drawings but nobody seems to have any. Seems pretty impossible to do without that. I've paid mechanics to put on a custom temp sender assembly in the rad return hose connection but never got it to work for whatever reason... anyway as I previously mentioned THERE IS NO LEAK. EXCEPT when overheated there's coolant coming out of the fittings etc... which is completely normal in that situation. The rad is new and the system holds water JUST FINE and was completely full of coolant just before I left on this trip. I checked it out beforehand.

sidriptide - see above - the rad was FULL and there is NO LEAK or drainage from the rad previously. the 'system' is FINE in terms of leaks is fine except that it does not cool the engine for whatever reason (this is why I am questioning the t-stat). i drove a few hundred miles to the desert and back without losing any water in the rad a few days ago... so...

I have purchases several XJ's that never would get up to temp and after driving for awhile then deciding to look into it I discovered that they each were running without a t-stat. I don't think its bad running without one but your engine will never get up to running temp and I think all that really does is mess with overall performance and MPG.. If anything replace your T-stat with a failsafe brand one and if it ever gets too hot it will stick open allowing constant coolant flow instead of sticking shut and restricting flow like it seems yours has done.

Thanks for that... I guess i'm going to just do the t-stat and see what happens. But how to find a good one? I think I bought bosch in the past -but i'm pretty sure it all comes from the same factory in china... seems a pity they are designed in such a way that they get stuck closed rather than open... I'd rather have crappy MPG than lose an engine...

I was just hoping maybe there was an easy(easier) way to ID a water pump problem before having to pull the fan and all that ... just in case it was the pump..

If you want to check the water pump just do the following

1. See if water is coming out the weep hole.

2. Loosen the serpentine belt and remove it from the water pump pulley and give the pump pulley a wiggle and see if it had play in it and also give it a spin to make sure its spinning freely with no weird grinding noises.

But I would bet money its the T-Stat. Its real easy and quick to replace and should be the first place you start before looking at anything else. Go to AutoZone and get a failsafe thermostat.. its like $12 and you will never have to worry about it getting stuck closed.. I use them in all 5 of the XJ's we have with no issue.

Okay- thanks man.. i'll ask for that... hopefully they have them. good idea. good idea on the WP check too - I probably knew that at some point but forgot. Seems to me that WPs get pretty loud when they fail though - haven't heard any squeaking out of the thing... thanks again

If there is no leak, as you insist...where was all the steam and coolant coming from??

As a general rule for diagnoses...

Overheating in traffic, around town, slo n' go it's an AIR CIRCULATION problem (fan clutch) or restricted air flow.

Overheating at speed...highway, it's a COOLANT FLOW problem. Restricted circulation, WATER PUMP, radiator clogged, heater core etc. (Since you have a 98 you have no heater valve so the coolant should be continuously circulating thru the core...unless it's clogged.

If it's a combination of problems, overheating anytime, it's likely a combination of AIR and COOLANT problems.

I would seriously doubt a stuck closed t-stat is the problem since you had already driven some distance...it would have overheated quickly if the stat was stuck closed.

ParadiseXJ

I have no idea where it was coming from - various fittings and joints all over the cooling system and engine i should imagine. clearly there was no circulation of coolant going on...

ALL vehicles and cooling systems 'leak' under extreme temperature stress in some way - that doesn't mean the vehicle 'leaks' - when we use the term 'leak' we are referring to 'during normal operation'. I lose no rad fluid under normal conditions at all. My radiator and all hoses etc are pretty new...

the point being that the overheating did not start because of an absence of coolant (if you care to read my initial post)

NeXJ said:

ParadiseXJ
(if you care to read my initial post)

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Wow, love guys like you. Ask for input, get it, think that it's wrong or not correct, and then you're snide and condescending.

NeXJ said:

...when we use the term 'leak' we are referring to 'during normal operation'.

Click to expand...

1leak

verb \ˈlēk\ .
: to let something (such as a liquid or gas) in or out through a hole in a surface

Webster's says nothing about normal operation.

That said, there are two places that liquid can leak from during "normal operation" even though the system is not operating normally. The cap, which would indicate a faulty cap or the overflow bottle, which would indicate too much pressure in the system OR a faulty cap.

When I have had an overheating engine, coolant has escaped (leaked) from both the cap and the overflow bottle. Each of these indicates that you have a problem. When the engine builds pressure it SHOULD relieve that pressure through the cap in to the overflow and when the pressure reduces that same expelled coolant should be recovered by the cooling engine. THAT'S normal operation.

Since you have ignored the possibility that you have a problem while driving your Jeep in the desert with no temperature gauge only by the fact that your e-fan keeps cycling, it is NOT operating normally.

So I really don't care if you had to push your Jeep to a Shell station or a Chevron station, whether coolant was spewing all over the engine, smoking, steaming or whatever, all I read was overheat, help, diagnosing, and alot of coolant spewing. I gave my best shot at helping you.

I'm not worried about it. it's your Jeep. You can be as smarmy as you like. I have a thick skin, I've raised 4 children and I work with juvenile delinquents. So, go get an AutoZone failsafe thermostat...that's probably it.

atriot:

Trailbst said:

Wow, love guys like you. Ask for input, get it, think that it's wrong or not correct, and then you're snide and condescending.

Click to expand...

Hi - I apologize for appearing that way but it was just mild frustration since I think people were reading the initial post and saw the word 'leaking' out of context and latched onto that. Probably my fault for being overly complicated - but I DO find that if I present an overly simple picture (i.e. - just overheated what to do?) then people ask for more information - which is good - but I thought I would try to provide it all first... the point was simply that no leaking happened until the engine overheated... hope that's clearer.

ParadiseXJ said:

1leak

verb \ˈlēk\ .
: to let something (such as a liquid or gas) in or out through a hole in a surface

Webster's says nothing about normal operation.

That said, there are two places that liquid can leak from during "normal operation" even though the system is not operating normally. The cap, which would indicate a faulty cap or the overflow bottle, which would indicate too much pressure in the system OR a faulty cap.

When I have had an overheating engine, coolant has escaped (leaked) from both the cap and the overflow bottle. Each of these indicates that you have a problem. When the engine builds pressure it SHOULD relieve that pressure through the cap in to the overflow and when the pressure reduces that same expelled coolant should be recovered by the cooling engine. THAT'S normal operation.

Since you have ignored the possibility that you have a problem while driving your Jeep in the desert with no temperature gauge only by the fact that your e-fan keeps cycling, it is NOT operating normally.

So I really don't care if you had to push your Jeep to a Shell station or a Chevron station, whether coolant was spewing all over the engine, smoking, steaming or whatever, all I read was overheat, help, diagnosing, and alot of coolant spewing. I gave my best shot at helping you.

I'm not worried about it. it's your Jeep. You can be as smarmy as you like. I have a thick skin, I've raised 4 children and I work with juvenile delinquents. So, go get an AutoZone failsafe thermostat...that's probably it.

atriot:

Click to expand...

Paradise - I was only trying to make the point that there were no 'leaks' up until the overheating. I think that's a pretty critical piece of information that needs to be looked at (?) or am I wrong? Sorry for coming off as cranky. I was just trying to keep the topic on point... if we were to discuss where the 'leak' came from after overheating - then we'd be discussing chasing wild geese it seems to me - i.e. 'steam coming out of the cylinder head or oil pan' - it seems to me that the oil pan had little to do with the reason for the overheating etc... it is a good point about the overflow bottle though- because a lot of that 'steam' probably came out of there - since I maxed out the coolant before setting off - including 'filling' the OF bottle as a precaution...

and I AM thankful for your help - to everyone... I haven't been doing much repair work lately and thought maybe my assessment of a bad t-stat might need a bit of 'checking'...