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A Coolant Conumdrum

12-12-2009, 08:31 PM
I recently had my '95 Geo Metro's water pump replaced.
I thought it sounded quite loud and was several years (or more) old.
It was fine....but now I have a new Water Pump....

BTW - it still sounds as loud as the old one did. Metro engines must
be inherently noisy.

Been driving the vehicle for about one month with the new WP.

The last couple of weeks has seen COLD weather - two days down to 2 F
during the night.

The car's heater wasn't putting out heat as per usual as it did last winter.

Long story short - the Temp Gauge fell on my way home two days ago - no heat from the heater, either.

Thought perhaps my Thermostat (Gauge temp has been varying) was going out - they fail OPEN.

Got home and left it overnight.

Checked the Coolant Level next morning - none visible in the Radiator and the reservoir was empty !

Had not seen ANY coolant leaks on the ground anywhere.

Refilled the Radiator with 50% Antifreeze (what was in it originally) while the engine ran.

Took about 1/2 gallon - more or less.

Now the heater puts out lots of heat, but the Temp Gauge is in different positions after each startup
(mid, high, mid, mid, high, etc).
Still think the Thermostat need replacing.

I have looked everywhere for leaking Coolant - while engine running, parked, etc - can find NO LEAKING !

Here is my only conclusion (am I full of Sh*t ?) - there was a large bubble in the system when the
mechanic refilled the Coolant after installing the WP and it took all that time to burp out...

...or could I be burning Coolant (leak in the Head Gasket) ?

No Coolant in the oil - oil looks good on the stick.

Otherwise - "it is a puzzlement" ! :confused:

The power seems to vary from day to day also. Very odd.

I will see what the next few days brings.

Any ideas ?

Could the 2 F temps have caused leak that sealed back itself up ?
How about the "O" ring on the pipe coming out the back of the WP ?


12-13-2009, 05:22 AM
Don't know, 1/2 a gallon is a BIG bubble, don't see how that could be. Our cars are prone to bubbles though, jack up the front end and let it run for half an hour with the cap off. Keep a pan under the radiator and keep pouring it back in the top while the bubbles come out.

What do you mean by a different temperature every time you start it? My temperature gauge points to C when I start it, slowly climbs to dead center, then never moves for any reason whatsoever. O degrees with the heater blasting or 100 degrees stopped dead in traffic with the A/C on, that gauge is always at dead center.

12-13-2009, 09:11 AM
my experience of the gauge is the same as woodie's .... gauge almost never moved from center ....until i rebuilt the engine and replaced the cooling system parts. been watching the new fluctuations with the cooler weather and trying to establish a new 'baseline' for gauge expectations. been occasionally checking / corroborating temps with an ir thermometer and so far they are right on.

will be watching for your reports bill .... you'd see residue from the coolant if it was leaking externally. big bubble indeed if that's what it was. just keep coolant in it and watch carefully .... would be a shame to loose that new engine.

12-13-2009, 09:36 AM
Yesterday was the first day that the Radiator needed refilling.

I'll keep checking every time I drive it - you bet!

As to the gauge position - it changes from one spot to another once it is at running temp,
then is rock steady at that position.

That is, once the engine has been running a long time (10 minutes), the gauge needle
sets at a different position each day - "more or less".

Said differently - the gauge is extremely steady, but it goes to and stays at a slightly
different running position each time I start the car up cold.

.........somewhere between midpoint and just off the top mark.

Not a lot of room there to move around in, but the temp gauge is a gauge I study
very carefully - I watch it continuously.

This started happening maybe a year ago. Figured the 180F Thermostat I had placed
in there when I rebuilt the engine was starting to fail.

A year ago I actually bought and have in the back compartment a 180F Thermostat
just in case I need one quickly.

I had read that the sign of a Thermostat going bad is movement of the Temp Gauge
from time to time - which is happening.

Either the Thermostat is slowly failing or maybe I have bits of crap in the Coolant
that are getting into that gap in the thermostat plunger.

Anyway - not Rocket Science, but it is a puzzlement !

Once I am convinced that I do not have a leak, I will rest easier.

A leak can cause a catasterstroke....a bad thermostat is just an annoyance.

I could change the Thermostat in a half hour except for the fact that I'd have to drain the Radiator
and change it OUTSIDE and it is colder than a Witch's Boobies on Halloween right now !
Snowed last night...

I'll keep everyone informed.

Meanwhile, I carry two gallons of 50% Coolant in the car with me at all times.

As to a stable internal bubble, the heater just did not seem to put out much after
the mechanic replaced the Water Pump...which leads me to suspect a STABLE
INTERNAL BUBBLE was in there. Hmmmm.


PS - If Coolant was leaking into the cylinders, wouldn't I see it in the oil - emulsified?
Or else the high pressure exhaust would be getting into the Coolant...(?)

12-13-2009, 12:48 PM
appreciate your detailed accounts.

coolant can go a lot of places ..... can be blown out exhaust but that might be hard to see in your climate. exhaust in the cooling system heats and pressurizes. so far it doesn't sound like that but .....

one potential problem i noted ...if the heater hoses are positioned badly they might bend or kink shutting off flow. too long might make a 'high loop' trap also. that yours ran well for a long time suggests this is not the problem.

back at the tstat .... i was unhappy with the 180 and went to the original at 193 if i remember correctly. the 180 aftermarket stant did not seem to respond / control well .... gauge seemed to be 'hunting'. i went to the dealer and got a pricey oem tstat and that seemed to balance well. unlike yours, my fluctuations have been on the lower side as i'd expect in cooler weather if i hadn't had the 300k miles with a rock steady midpoint gauge. the dynamic pattern is the same however. cool start, heats to point of opening tstat ... about 3/16" below mid ... and falls back quite a bit as the new cool water passes the tstat and sensor. then the whole system heats and the gauge goes to somewhere between opening point and mid gauge .... and that point is reached after shorter or longer times and goes to a higher or lower position depending on outside temp. after longer drives, the gauge seems to slowly work its way to mid point but i have not driven it yet in freezing temps. the heater can keep the cabin very warm even at initial heating and low gauge positions i note but again, i live in a much more temperate zone.

summer is different. runs very near mid point and under idling or hard load and high outside temp conditions, rises above mid maybe 1/8" and then the fan cycles and brings the gauge back to mid or just under before it shuts off.

after the rebuild i finally chose a 2 row radiator core vs the original one row .... so i've expected some differences.

Metro Mighty Mouse
12-13-2009, 09:05 PM
A note on blown head gasket symptoms. From personal experience it is possible to have no evidence of coolant in the oil. I had a bad gasket for a few months before I was finally able to diagnose it. The main symptom was mysterious coolant loss, kept having to refill the radiator over and over and couldn't find where it was going. No spots on the ground, no real evidence of where it was going. I then started to notice a gray clay like material caked in the overflow. With the car sitting at idle or revving with no load no coolant could be seen exiting the vehicle. Finally, going up a hill under heavy load, major power loss and cloud of smoke behind me. After slowing and playing with the throttle it cleared up and I continued to work. At this point I figured it was probably the head gasket and I started looking for other proof. During this time, no smoking, plenty of power, just missing coolant and gray stuff in the overflow. After a few weeks there was a repeat of the smoking power loss on the hill and I started really digging for proof it was the head gasket. Looking in the overflow, it had finally started bubbling into the overflow at idle and when not under load so I could see that engine compression was pressurizing the coolant system. With the hood off I could see coolant spraying from the overflow at speed. So there are a couple of things to look for to determine if it is a head gasket.

12-13-2009, 11:10 PM
It sounds like you have a small leak. Here's a few things I would check.
Smell your exhaust. Although its usually a significant head gasket leak, it can make your exhaust smell a little sweet and you can see a little steam vapor even after the engine and exhaust has warmed up.
Check your coring plugs. they can weep just enough so that you won't see a drip. The coolant can dry as soon as it exits the engine.
Don't assume that water pump is not leaking just because its new.
Check you hose connections especially at the heater core. That's an area that may be hard to see. Coolant may weep and dry before it has a chance to drip or it can run down on the inside of the fire wall. Check you carpet.
Then you may want to pull your plugs. If you have a leaking head gasket it will usually steam clean one or two of your plugs.
I would definitely change you tstat. Although the temp gauge can act that way if you are low on coolant, you said you just filled it and it still does, so that means tstat.
Just my opinion but I've never been a big fan of the cooling system bubble theory. Yes I know there could be a small bubble here or there when first filling a system, but not big ones and after a few warm ups and cool downs they work their way out. I find it very hard to believe that engineers would have designed an obvious flaw like that, and even harder to believe that they jacked up each car at the factory just to fill the cooling system.
Hope this helps.
P.S.Run the engine before you work on it to keep your hands warm.

12-15-2009, 05:22 PM
I have my own problem, but I dont want to hijack this thread. I do want to throw in my 2 cents about this thread.

I have a 94 metro TBI (VIN 6), and I count 5 temp sensors.

Thermostat Housing:
One wire sensor runs the gauge only: 0V=flat, 12V maxed out
Two wire sensor runs the electric coolant fan

Throttle body:
two wire sensor feeds the ECU (mixture temp)

Intake manifold:
one wire sensor, unknown connection, suspect feeds ECU
(undocumented in the glorious haynes manual)

Air filter assembly:
Air charge intake sensor, unknown connection, suspect feeds ECU

All that said, a few years ago, my temp gauge was acting quirky. Being an electronics tech, I quickly determined it was intermittent, so I suspected a bad connection. On the end of the one wire gauge sensor, the spade connector is attached with a brad, or pop rivit of some type. If the spade connector seems loose, this is your problem. Took me a minute to figure this one out, but it did fix the problem. I put the sensor in a vise, use soft jaws so you dont booger up the brass. Take a (small 4oz) hammer, and gently tap the brad. If your hammer is too big, use a pin punch. Unfortunatly this seemed to only last a few weeks or months before the mechanical stress from the wire caused the problem again. For a more permanent fix use a 80-120 watt soldiering gun to soldier the spade connector to the b rass. You will need to prep the area so the soldier will stick. I dont reccomend torch welding this as propane could overheat the resistor inside and burn it out very quick.

Also FYI, I had to call the dealer to get this info, but the intake sensor is the exact same sensor as the gauge sensor in the thermostat housing.

I dont know if any of this applies to your 95, just thought I would pass this along.

Hope this helps.

12-16-2009, 06:51 AM
The one on the intake manifold is for A/C shutoff in the case of overheating.

12-16-2009, 05:47 PM
The one on the intake manifold is for A/C shutoff in the case of overheating.

interesting. thanks a bundle for that info. I always wondered what it did.

12-25-2009, 12:25 AM
I finally caught the bugger dripping Coolant, so I popped the hood
and saw it dripping from a hose in the middle of the compartment.

Didn't have time to look closer as I was on the way somewhere.

Stopped and bought 2 ft of hose and will find the damned leak when
all this Christmas fallderall is over.

I think it is the small hose coming out of the pipe to the Thermostat
that goes back to the Firewall (?)

Must be some kind of pinhole as the tubing looks very good...

Am happy it is a hose and not a seal or freeze plug !


12-25-2009, 05:01 AM
Heater hose. Probably leaking at one end and running to the lowest point before dripping off.

12-26-2009, 07:10 PM
It is 24 outside - I bought some hose, but I think I will take it to the
shop where I had the WP changed out and let a mechanic fix it in a
nice warm Garage where a younger man can see WTF he is doing.

I am just too old and half blind and can't take the cold anymore.

Lovely thing getting old.....

You young fellows don't know what is in store for you !

Enjoy your Youth while you can.

And BTW - Merry Christmas to everyone !

...and I don't give a rip if it isn't Politically Correct anymore to say Merry CHRISTMAS.


01-01-2010, 08:02 PM
Took The Phoenix to the shop and they discovered what was leaking...

I had put in a Flushing Tee several years back and apparently the cap was
slightly loose and it was losing fluid that way !

Never leaked before - only after they had replaced the W.P.

Anyway - something as dumb as that !

Back in business....


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