Car Question

[AlohaDawg]

Perhaps best answered by Asherdan who also wrenches on jeeps:

I just yanked a leaky water pump off my truck. Second time in 3 years this has happened. The water pump is basically made of galvanized pipe with an impeller connected to a pully that is turned by the engine belt with a line in. It seems like it should be close to indestructible - it's all metal.

It has a tiny, perfectly round hole in it. It's not seized; it turns just fine.

How does this item get a hole in it? Is it manufactured, then drilled and epoxied to give it a life cycle? Even under heat and pressure, wouldn't it crack rather then blow out a hole basically the size and shape of a BB?

[AugustWest]

Psychic stress.

[Ben-San]

If I were to guess, totally uninformed and assuming a basic goodness of mankind and practicality of design rather than pure profit motive, I would suspect that it is a plug such as you describe, except that instead of being a device of planned obsolescence it is intended to fail under excessive pressure and be easily replaced rather than having the entire pipe or something else important rupture.

[side_show]

Huh, I just spent the afternoon replacing my water pump yesterday too.  My car over heated due to a burnt-out fan motor and the hole in the pump happened during the overheating.  We replaced the motor a couple days ago to no unusual results, but with the hole in the pump didn't want to run the car until the fan kicked in with no engine coolant in the system.  As for my pump, It too had a hole (not crack) in it.  The whole wasn't little but was round.  Maybe it burst open, from the overheating and build up of steam?  I didn't think on it much since I have a far more mysterious problem:  now that I have put in the new pump and replaced the lost coolant, my fan now continues to run even then the engine is turned off.  I had to manually unplug it to keep it from continuing to run until my battery died.  It is so bizarre to see the fan continue to run when the engine's turned off.  I'm thinking through overheating that the temperature gage is somehow misreading the current cool engine as being too hot.  Is it  actually possible for a temperature gage to get stuck on hot?  I'm going to drive it for a bit and see if it re-calibrates itself.  If not, I have to get the Chilton guide for my car and figure out where the gage is and see what's up.

[AlohaDawg]

If your thermostat temperature gauge isn't showing the car overheating (and I assume you have a engine belt-driven fan and an electric fan?) I would suggest finding a friend with a computer tester to hook up and give you the error codes, and look them up on the internet. I'm thinking you might have an issue with your fan relay; an electrical problem rather than a mechanical one - why it would continue to run even after the key is out of the ignition is odd (or considered a 'feature' by the designer); mine won't go on unless there is a key in the ignition. Did you replace the thermostat? It's a cheap part and easy to get to - once you've had a major overheating problem it's a good thing to replace since there's no obvious way to test it.

So it took me over 2 hours to put the fackin' new pump on last night; there is a pipe that goes to the heater core that is bent so it can't be removed while the fan is installed because the bent part runs into the cylinder head cover. But, it's on so tight that it is impossible to remove with the pump off unless you put the old pump in a vise and brutalize the thing 'til the fitting breaks loose. Then you have the problem of rinstalling the little fucker BEFORE you put the pump back in. My favorite part, though, was the hour or so I fought with the 6 bolts that are three different sizes since I couldn't remember which went where. It was like a real life logic puzzle. I got black gasket goo all over my hands fighting with the thing.

Basically I got it all connected last night except for the serpentine belt, so today I can fill it with water and see if there are other leaks, and start it and see if it blows up. Still got the head gasket to deal with too, but it will take short trips around our little town right now.

Ben-san, I think you may be onto something. The new pump has two perfectly round holes in it; one is roughly in the same spot. Perhaps there is some kind of seal there that is intended to blow to prevent overpressure in the engine. Seems like the radiator cap would pop first, though.

[Asherdan]

'Dawg - Ben is essentially correct. The radiator is going to be to coolest part of the coolant system, there can be a huge temperature differential between block and radiator temp. So the water pump, which is getting the hottest water direct from the block passed through it has a pressure bleed built in as well. It's prolly a more important measure than radiator temp/pressure 'cause if the block temp spikes that's when something very expensive can bind up and go blooey.

Jeeps with the 4L engine tend to run hot. If your radiator isn't in top shape you're in the kind of climate that can run engine temps right past the 220f threshold of car trauma. When my last Jeep started running hottish and the radiator was old enough to be inefficient I took it to a local shop (Stanton Radiator) and had them keep the end caps and replace the two core vane set with a three core vane set. Essentially I got ~50% higher coolant flow/capacity and greater vane surface area. I don't know your local costs (here ~$200) but that may be a worthwhile investment. If an engine runs cooler, at the low end of its reccomended range, it's going to live longer and with less trouble.

Smells has a possesed car fan!

[side_show]

Yeah, it is indeed possessed.  My personal car expert (aka Dad) tells me that the fan will indeed continue to run (for a brief period), even with the ignition turned off, if the engine has over heated.  I again re-plugged the fan in with out the engine running or keys in the ignition yesterday, and again, the fan started running.  I left it to run for a bit, but it is clearly not shutting off, and I don't want to kill my battery, so I unplugged it again.  The engine temperature gage on my dash works fine - I watch it carefully (since my fan's not hooked up) and as the day grew hotter/I drove the car more, the gage went up.  I'm guessing something with the internal computer is toasted, and permanently thinks the car is over heating, but am waiting to get my car manual from the local library, and will take one more whack at it, maybe re-do the wiring or replace the thermostat itself, before I turn to a shop.  It does seem a little odd, but really all sorts of components of a car keep functioning when the ignition is off... it's just that this one shouldn't be.

[AlohaDawg]

I'm not an expert but it seems odd that that one really minor function of the computer would get toasted (assuming you don't have other issues). I vote for a bad relay - for whatever reason the circuit is locked open. The Chilton's guide is awesome but damned if I can puzzle out the wiring diagrams. I still say find a friend with the electronic diagnostic tool and have them check it.

Ash, I looked up a problem on the intarweb and found at least 4 others with this issue:

Driving along, doot-do-doo, and the airbag light comes on. A second or two later, the dash gauges all go dead simultaneously. They come up and down at random, no correlation to hitting bumps in the road or other indications of a loose connection.

Turn on the left turn signal and they come back up. In my case, also push in on the pullknob for the headlights and they come back on. It seems that if you drive awhile, they come on and stay on.

Got a theory?

Also, against everyone's advice and contrary to their expectations, I used a coolant additive and succesfully (so far) repaired a blown head gasket. I'm as amazed as anyone that it worked. When it blew, I couldn't go much over 20 without massive valve noise and no power at all. Now I can do highway speeds and go over the mountains to work.

Still planning on replacing that gasket myself when I get more comfortable with all the stuff under the hood, though.

[Asherdan]

I'm not an expert but it seems odd that that one really minor function of the computer would get toasted (assuming you don't have other issues). I vote for a bad relay - for whatever reason the circuit is locked open.
----------
Got a theory?

Smells, it really is kinda a one fail/all fail thing (or at least, more than one failure) with the control module. It'd be very worthwhile diagnostically to figure out from a wiring diagram where the fan is getting power from and what part controls the power on/off switching. It should leave you with a choice of two parts to replace, one of which is a relay that wouldn't hurt to replace on an older car regardless.

Theory for 'Dawg

I haven't had that problem with a Jeep, but I know many people have been irrevocably turned off on them because of such 'bugs'. Jeep even did a complete wiring run redesign post '96 model year in order to eliminate some of the recurrent electrical faults.

What you're describing sounds like a wiring/harness issue behind the dash effecting the gauge/idiot light feeds and I'd check first near the steering column. Feel like taking the dashboard out to check on this? (take your multimeter)

Me neither, that's why those types of issues suck.

[AlohaDawg]

I haven't had that problem with a Jeep, but I know many people have been irrevocably turned off on them because of such 'bugs'. Jeep even did a complete wiring run redesign post '96 model year in order to eliminate some of the recurrent electrical faults.

It's a 98 - woulda thunk they got it worked out. I have the guide so I know how to pull out and replace the instrument panel. My hope was to identify the power supply to the panel and check the connection and the circuit. I'll have to buy a mulitmeter (just another toy I guess) I've not done this before. Is the wiring such that I could replace ALL the wires under there, by buying a set of appropriate wires with connectors on both ends? By all I mean the power to the gauges and the wiring between the gauges and the module or module relay? Also maybe the stem for the wipers and the switch for the headlights?

[Asherdan]

I think you're on the right path, though I would think the problem probably lies in the power feed rather than the wiring itself. On first visual I'd check for wire and connection damage, if none is visible, which is likely, then start checking electrical feed from main power module to end of run. The tricky part is doing that in 'normal' state then checking in 'fault' state to see if you can pick up what component is faulting.

The purchase items, particularly the wiring harness, sounds like a dealer item. It might not be available then, or after a long warehouse inventory search because the Cherokee went out of production in '01.

They never did fix all of the Cherokee's electrical issues, it's a known issue type thing.

[AlohaDawg]

Are t hey still making the Grand Cherokee? Same Chilton's so I'm hoping some of the parts should be available. But yeah, thinking about it more the problem is clearly in the power supply and I'm thinking there is somehow a short that either originates in the stem for the turn signals or touches something metal common to the blinkers and the headlamp switch. It's too weird for both of those to be be involved (unless they are all running through a common fuse box or relay...)

[Asherdan]

(unless they are all running through a common fuse box or relay...)

I hope they are, 'cause when I think about it it sounds like your voltage regulation has reached expiration age. At normal operating power requirements you get display issues, when the power requirement rises (signal, headlamp switch) you thwack back into normal function. What that sounds like to me is an electrical part in a power management module going bad.

And yeah, they're still pumping out the Grand Cherokee in Michigan, so you may have component part luck.

[AlohaDawg]

That is such a sound theory that I will check that first. Thanks!

[AlohaDawg]

I have to belay the electrical issue until I can

a) replace my head gasket and

b) replace the neutral start switch. Ever done that one?


Also, is there a solvent I can use to clean the black gasket sealer crap off a painted exterior car surface?



dammit.