Re: Finding coolant leak and checking temp gauge

[michaeld]

Hi guys,

I've got a 77 450SEL 4.5L w/ 126,000 miles.

Some time back my water gauge began to read hot, but there were no other symptoms of an overheat. Three mechanics (and two radiator shops) told me I was NOT overheating. The last mechanic was a personal friend who had owned a transmission shop for years: he checked the system using a thermocouple and measuring the temp at the water pump 212F switch, the top radiator hose, and the expansion tank, and telling me I was NOT overheating, as my temps were all under 180F.

QUESTION 1) Was the above test a valid measurement of my cooling system, or misleading? I know the temp sending unit is in the back of the engine, and I know there must be some insulation factor (i.e. the metal body of the water pump/switch, the rubber of the hose, the plastic of the tank). I'd sure like to know.

In any event, I've had to make several hundred mile drives, and my gauge would always be reading 240F+ by about 25. I've always pulled over midway on the drive. But last week I decided that the gauge was just wrong, and to make the drive (though I was STILL paranoid). At 60 miles I saw steam coming from the right side of the hood, and got right off the freeway.

I got towed home (the ignominy!) and the next morning added coolant to bring the expansion tank to the cool mark. It took 2 quarts. The level droppped a little bit when I started the car and drove it into the garage, but I figure I couldn't have lost much over three qts.

I didn't know where my temp sending unit was - or I would have done this sooner - but I tested the unit by measuring the resistance in water at various temps. The sending unit seemed fine. Here's the results
60C/140F -> 107 ohms (cf 110 ohms spec)
80C/176F -> 63 ohms (cf 67 ohms spec)
90C/194F -> 46 ohms (cf 51 ohms spec)
100C/212F -> 38 ohms (cf 38 ohms spec).

I then measured the sending unit in boiling water connected to the gauge in the car. At first my makeshift ground came into contact w/ the single pole, and my gauge was reading max redline. But once I figured that out, I got "sane" readings which I don't fully understand. I was trying to get boiling water, but by the time I got the pan into the engine bay, and the sending unit into the pan, the temp invariably had decreased. But my measured temperature was 190F, and the car's temp gauge read 175F. And the gauge continued to read 175F until the actual water temp was 148F, at which it began to drop a little.

QUESTION 2) How should I interpret these readings? Something seems hinky w/ this temp gauge, but it is not giving me the high temp readings I saw while driving. And, given the fact that the resistance of the sending unit actually DROPS as the temp increases, I don't understand how old wiring (which would have a higher resistance) could be the culprit.

My fear is that I was actually driving hot all along, and that the too-hot coolant caused a component to fail. I am suspecting that my ACC servo blew up, but it could also be the heater core.

QUESTION 3) How would you go about finding the leak, and verifying the heater core is okay/bad? I have a dye/UV light leak detector, and I can get a pressure tester at AutoZone on the loan-a-tool program. Should I start the car and let it run until I see a leak, do a pressure test and look for a leak, or connect the pressure tester to the car and THEN start it? And what would I see if the heater core was the source of the leak?

And,
QUESTION 4) If I were to try to purchase an auxilliary water temp gauge, and measure my OEM unit against it, would I connect it to the OEM sending unit, use an aftermarket sending unit, or connect the temp gauge to a different water source altogether?

At this point I am intending to take the car to a German car mechanic (MotorWerks in Palm Springs), but would like to do as much as I can prior to doing so.

P.S. The water pump is less than five years and 10,000 miles old, the radiator core was replaced 1 year and 6,000 miles ago, fan clutch engages (it passes the "rag test"), and the aux fan DOES kick on. I've never seen white steam out of the tail pipe, oil in my coolant, or signs of coolant in my oil (at very recent past scheduled oil change, the oil looked nearly new and there is no white gunk in the oil cap). Also, I have not been losing coolant prior to my disaster on the freeway.

QUESTION 5) If I AM overheating, what in the heck is causing my problem?
Mike

[juribe2]

Hi,

I think you could check 3 things:

1. Check / replace the thermostat. Is a cheap element and if it get stucked you're car will overheat. You can put the thermostat in a pan with water on the stove and check the temperature to see it it opens when it is supposed to. In my car (W124, M104) it opens at 87 C.

2. Check /replace the radiator or expansion tank cap. The cooling system needs to be under pressure to keep the temperature low. Again, is a cheap element and makes a big difference.

3. Check for coolant leaks. There are 2 easy ways to do that. If you can rent the radiator pressure tool, install it with the engine cool and apply pressure to the system (about 1 to 1.3 bar). The pressure should hold and if you have a leak the pressure in the system will push the coolant out and you will see the leak and pressure will drop quickly. You can also use this tool to check the radiator cap. The other way is to drive the car for 5 minutes to get pressure in the system and check for leaks with the system hot and under pressure. Don't remove the radiator cap while doing this. It's dangerous. Doing this with the engine hot (but not running) is unconfortable but is a way in case you don't have the pressure tool. That way I discovered a crack on my expansion tank yesterday. It did't leak with the engine cool but It did leak a lot under pressure.

I hope this help.

[meltedpanda]

do you have air in the system? If you have had parts on and off you could have some trapped air . You have to burp these babies
The other possiblity is an obstruction of some sort, do you have heat?, how long does it take to respond to the hot cold thermostat?

[230/8]

Mike:

It sounds like you have a leak. If you added 2 quarts of coolant then it went somewhere. (What would this be, 15% to 20% of your total coolant capacity?) If you see no signs of an external leak, then you are left with an internal leak. With all the possibilities out there, I would suspect a head gasket or manifold gasket.

Your sensor performance against the specs seem reasonable so the gauge is probably telling you the truth, the engine is hot. The loss of coolant would tend to confirm this...along with the tow truck bill.

Last thought...the radiator cap does not keep the temperature low. It raises the boiling point of the mixture under pressure. This allows coolant to maintain itself in a liquid state at higher temperatures inside the engine around the hot-spot areas, rather than boiling to a gas, which prevents heat transfer into the coolant. The thermostat regulates temperature levels between the engine and radiator.

230/8

[meltedpanda]

Originally Posted by 230/8

Mike:

It sounds like you have a leak. If you added 2 quarts of coolant then it went somewhere.
230/8

230/8 is right, shoot I missed that part of your post. I had a suburban that blew a head gasket, I never saw any white smoke out of the exhaust. Without fluid circulating then you got an overheat problem.
If you fluid is going down and no external leaks, no where else it could be going but to the cyliners to be burned

[michaeld]

Hey, guys.

Oh, I've definitely got a leak. And it appeared to be quite external. I should have been more clear stating that bit of trivia! My only question at this point is whether it's the ACC servo, the heater core, or both.

As I was driving on the freeway, I suddenly became aware of the fact that there was STEAM coming out of my hood on the right side near the ACC servo. I was FREAKED OUT and got off the freeway right away.

When I got to a gas station right off the freeway, shut the car down and popped the hood, I saw steam and heard escaping air and droplets of coolant coming out of the right side in the vicinity of the servo. It looked like it was the servo that was leaking. A puddle of coolant gradually began to form under the car. It was awful.

I hope that I didn't damage my engine. I notice that the 2 quarts that I added disappeared and that the expansion tank seems empty. So at this point, I have no idea how much coolant I actually lost.

When I said I wasn't leaking coolant, I was speaking about prior to the above "catastrophe." The gauge was showing hot, but there were no other signs of overheating. THAT was when I wasn't leaking. Three mechanics told me I wasn't overheating. Three mechanics may well have been three idiots - and add me to the list.

I obtained a pressure tester, and will need to add coolant to the cold level to use it. Since I don't know how much coolant is absent (and I will keep tabs on how much I add as I pour it in) I will be very careful about starting the car. I figure I will probably HAVE to start and run it to get it hot before I actually see anything, tho. Fortunately, I have one of those dye-UV light kits to help.

First I've got to address whatever is leaking and fix it or bypass it. Then I've got to deal with my cooling system woes. One of the things I might do is buy an aftermarket gauge and test the old one with it. Once I get the leak issue corrected, I will probably take the car to a German mechanic to diagnose the overheating issue (assuming the second gauge reads hot as well).

BTW, I did change the thermostat and the pressure cap several months ago. The thermostat is THE most likely thing to cause an overheating problem, and it's one of the cheapest items as well.

Thanks for the help. I need it!
Mike

[michaeld]

Oh, and BTW...

Would disconnecting the small hose between the radiator and the expansion tank be a way to check the water pump once the thermostat opened?

I'd sure like to know for certain whether that critter was doing its job!

[meltedpanda]

you should be able to see the fluid moving through the radiator with the cap removed. Of course the thermostat must be open so be careful using this method. You can time this with the opening of the thermostat whilst the engine is not too hot to remove (slowly ) the radiator cap.
Does the heater work?
Reposnd quickly or slowly?
Any sense of radiator fluid smell inside the cab?
With the puddle on the exterior, I would doubt heater core, can you trace the leak to the source, freeze plug, line, block crack?
Keep us posted and good luck

[Mike D]

If the servo is leaking it will dump 2 qts. of coolant quickly at engine speed. You won't notice much of a leak at idle because the water pump (essentially just a turbine) is barely circulating water. When engine RPM's increase the water pump starts circulating the water rapidly. This forces the water to flow through the heater lines much faster.

It might seem like insignificant "seepage" at idle but at full flow it can become quite a "trickle". Of course, since it's dripping onto the exhaust, most of the evidence of the leak is lost. Check the very bottom of the exhaust pipe header for evaporation marks.

[juribe2]

Originally Posted by michaeld

Hey, guys.

... And it appeared to be quite external. ...

...there was STEAM coming out of my hood on the right side near the ACC servo. ...

... I saw steam and heard escaping air and droplets of coolant coming out of the right side in the vicinity of the servo. It looked like it was the servo that was leaking. A puddle of coolant gradually began to form under the car. It was awful.

I don't think it's the heater core. When that happens you usually get coolant inside the cabin.

If you saw steem and heard escaping vapor, I would check for heater hoses first.

BTW, if you have the pressure tester you don't need to start the engine to check for leaks. Just fill the system and apply pressure (1 to 1.3 bar). Check if pressure holds and look for leaks with the engine cool.

I wouldn't waste coolant for the fix procedure. Just fill the system with water (good quality tap water or buy some potable water) to check everything and once you get the leak fixed, replace the water with coolant.

[michaeld]

Update on the current crisis:

For those just reading this thread for the first time, let me bring you up to speed. I've been showing a hot gauge, but have had no signs of overheat. Three mechanics said the system was running normally. One of them used his thermocouple to take temp readings around the engine (top hose, 212 switch on the water pump, expansion tank) - which were all under 190F - and assured me that I had a bad gauge. I used my own noncontact thermometer at home and compared to my other car that I KNEW was running right and got similar temps from both cars.

I went ahead and drove it and ignored the hot gauge, and then BAM - I see steam coming from the hood. When I got the car pulled over, I saw coolant and steam sputtering out of the ACC servo. (It was either coming from the servo or from the heater core, but not from anywhere else. It sure looked like the servo). I was getting whiffs of coolant, but I was NOT getting film/fog on the windhsield immediately prior to the disaster.

Back to the present...

Today I positioned the car on a slope engine up and started it. I was looking for leaks but also keeping an eye on the thermostat to open. I put in 2 quarts the day after the disaster to bring it to the cold mark; well, that gradually gravitated into the radiator and today I had to put OVER A GALLON of coolant in (That's over 6 qts for those doing the math at home)!!! I sure hope I didn't kill my engine over this. I was just looking at the expansion tank and the coolant I added 4 1/2 hours ago is still at the same level. Hopefully that's all I lost. [FYI: when I got the car off the tow truck, I added 2 qts to bring the level to the cold level on the expansion tank and drove it 40 feet into the garage. I did NOT leak a gallon of coolant after topping it off w/ the 2 qts. I have to assume the level was simply actually lower and gravitated into the system].

So anyway, I let the car idle for 40 minutes, and there is good news and bad news to report: the good news is nothing happened, and the bad news is... nothing happened. No leak ever seemed to develop anywhere that I could detect. No so much as a tricke. I used my dye/UV light kit to assist me in seeing a leak. I read MikeD's post, and understand what he's saying, but, well, you'll see as you read...

Does the fact that the car ran that long w/o seeing any leaking tell us anything at all? Does it rule in/out the heater core or the servo? I have not been able to find any cracks or bad hoses anywhere. Geez this is driving me nuts, and I've never been far from cracking completely!

How am I going to find this leak? I'd hate to drive it around until it explodes again.

Did I hear someone type, "Use a pressure tester, you bozo!" Well, I DID try. In fact I tried using not one, but two different pressure testers via Autoazone's loan-a-tool program, and wasted my time. You might not believe me, but I think I ended up with two bad loaner units (I'm not a mechanic, but have successfully used pressure testers a few times previously).

The first one had oil on the handle, and it pressurized, but didn't hold the pressure. I think IT had a worse leak than my car! I brought it back, and picked up a second unit. Try as I might, I couldn't get it to clamp onto my tank. Finally I took a good look at it - and it appeared some #$%!*&$@ had banged on the side of the clamping cap with a hammer, and warped its shape. I told them about the leak; I don't think I DARE tell them about the hammered cap, for fear they blame me for the stupid dumbass nonesense.

So, I'm still at square one.

A couple of things:
1) There was never any hint of smell of coolant in the cabin after 20 minutes of idling until I pushed the button to bring the ACC from lo to hi (set to cold). There was an immediate smell of coolant, and then it went away and never came back even after another 20 min.

2) I disconnected the small hose that ties the radiator to the expansion tank, hoping to see if my water pump was working. There was no flow. If the expansion tank is just for expansion, I suppose that is normal. If it is supposed to circulate, then it appears I have a problem there. What is the best way to check for water pump circulation?

3) On the issue of expansion tanks, let me add one more thing. I saw a light film on the coolant (before my abortive pressure test-attemp; now I don't see anything). It does not appear to be black and globule-ish, but rather more like grayish flakes or a gray dust-like film. I sure hope that isn't oil; but if it isn't oil, just what is it? Sludge from the engine? Hard water deposits? Beelzebub beginning to materialize in order to further screw with me? I saw the same stuff before my recent problem and just figured it was something like a lime-type deposit. FYI the coolant itself is clear and normal looking, not chocolate milky (or milky at all).

[meltedpanda]

I commend you for your persistance.....
My gut tells me the steam was from a very hot engine with very little fluid left, I think you have a cracked head. I have had an experience where fluid loss only occured when under load (hauling) and when up to highway speeds, turned out to be a cracked head. Have you pulled a plug to look at? May provide a clue. What does the oil smell like? Feel like?

[juribe2]

This is strange. I know how you feel. I've been fighting with my cooling system for 3 months now and had replace almost anything. Usually if you loose coolant but you don't see a leak, you could think about a cracked head or a bad head gasket.
How is you engine oil level? How does the engine oil looks like?

BUT, you said you saw a lot of steem and coolant leaking somewere near the AC Valve, so I think you have a different problem. Is your expansion tank in good shape? I had a severe coolant loose in my car and all hoses were ok. I had to fill the expansion tank twice a day and after a week looking for the leak, I finally found a very small crack in the expansion tank.

One more thing. Sometimes the hoses get small cuts very close to the tips and not somwhere in the midle. You have to remove the hoses to check for cuts under the fasteners. How old are those hoses?

Please let us know if you find something new.

[meltedpanda]

I have thought of another possibility
what about the loss of fluid at a gasket, hose or other that only presents when hot, underpressure and water pump at full output ( such as highway speeds)

[michaeld]

Hi, guys.

When I opened the hood following my disaster, what I saw was the climate control servo hissing and sputtering coolant. This unit is located on the firewall on the passenger/battery side. It was not coming from the engine, nor the expansion tank. Obviously, by the time I shut the car down and got out and opened the hood, I was seeing the hind end of the problem. The leak could have been coming from the heater core located almost immediately behind the servo behind the firewall. I THINK it was coming from the servo, but it is possible that both the servo AND the heater core failed. I'd like to rule one out. But I am positive that it is either one or the other (or a gasket/hose between the two units).

My oil looks good. I have changed the oil three times in this car since I got it, and I have always been very impressed by how clean the used oil has been. There is no sign that I have - or have had - any coolant in the oil. As for the coolant, I believe I'm just seeing scale or lime particles suspended in the solution. The coolant is a nice pretty shade of green; it is NOT "chocolate-milky." I've had several older cars, but none of them had an expansion tank; I'm wondering if scale is just something an older car has, or if it could be the sign of a problem (i.e. a blockage that has formed or is forming in one of the coolant pathways).

It occurred to one of my friends that since I had the pressure cap off the system never really got a chance to "do it's thing" leak-wise. That seems very possible. I'm now pretty sure I have all the coolant I'm supposed to have. I'm wondering if the fact that the coolant temperature never got above 180F tells me anything about the overall condition of my cooling system. I expect it to get to 176F because that's the temp of my thermostat; but it could have got to 212F even w/o the pressure cap on.

Here's my new plan of attack: I am going to tear out the glove box and try to get a really good look at the heater core/hoses. If I don't see a leak, I will assume the servo is busted and pull it out and bypass it - even if I can't recreate the leak (I'm just not willing to drive the car around until it fails). If I can get the system to leak either at idle (pressure cap on this time) or via a pressure test, that will tell be great. But I know it's leaking somewhere in the heater/servo area, and I've got to bypass something.

I also purchased a cheap water temp gauge (I won't hook it up right away as I would now have to drain the coolant I just added for the sake of testing the system. I don't even initially intend to route it thru the firewall; just hook the gauge up to the firewall in the engine bay and read it by getting out of the car and opening the hood. If - when I find my leak and fix/bypass it - I am still running hot, I'll take the car to Motor Werks and have them find the cause of my overheat. Otherwise, I'll permanently install a new water temp gauge.

I'm interested in hearing about what the presence of scale/lime in my coolant implies, and in what my temp readings (176-182F after 40 min at idle) tell me about my coolant system condition.
Mike