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Still overheating (grrrrr!)

Started by michaeld, 04 July 2006, 03:49 PM

Denis

Hi Michaeld

I think that you are making progress here. I also do not believe that you have a head gasket problem, especially if you have no "slime" in the coolant.

When a bad head gasket appears and the engine runs, its compression pumps fuel/oil into the cooling system : slime in the coolant. Since you are pitting 10 bars of compression against one bar of cooling system, guess who wins ::) and in fact, since the cylinders win, the cooling system pressure can become high enough to blow hoses, etc.

Since you have a pressure tester, can you measure your cooling system pressure with the engine running ?

If it stays normal, you should not have head gasket problems.

Good luck

Denis

Paris, France

michaeld

Denis,
Thanks for your excellent description of pressure testing.  The unit I used (Autozone's 'loan-a-tool' program) had no manual, and I really don't know all of the things these pressure testers are capable of.

One question: do I need to pump up the pressure on the unit before starting the engine, or just connect it and see how the gauge reads (I would presume the latter).

I may as well make the most out of the unit while I have it.  I still intend to check the vacuum and compression before doing any major repairs.  But completely ruling out a bad head gasket would be nice.
Mike

Papalangi

Mike,
Since the pressure tester won't vent like a cap will, it will rise dramatically at first and give you a false indication if you start cold with it on.  Start with the cap off and warm the engine to operating temp then put the pressure tester on.  It will stay near zero and rise if the temp rises but shouldn't go very high.  If it just starts taking off and hits above 16 PSI, I'd say you have a problem.

When testing the cap, as you pump and reach the cap value, the cap will relieve or vent so as to keep the pressure at it's value and no more.

The metal disk in the center of the cap is a vacuum release.  It allows air back into the system when things cool down.  In the case of the W116 with the remote tank, it allows the water pushed into the tank back into the radiator.

Michael
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8

michaeld

Thanks for that clarification, Papalangi,

You only have to close your eyes imagining my eye-popping reaction  :o followed by tears  :'( and culminating in anger  >:( that I would have had if I had put it on before starting the car and then suffered the result you are describing!  I will be doing the running pressure test as soon as I get home.  Thank you for sparing me that Shakespearean range of angst!

My cap does not seem to be opening (or releasing vacuum).  I ordered a replacment cap (as well as an upper hose, spark plugs, and an oil pan gasket) this morning; and will see what happens when I run the car w/ a healthy cap before taking her down to the mechanic or doing any additional work.

michaeld

Hi guys,

Great news!!!!!!!!!

I performed the running pressure test as per Papalangi and Denis advice and instruction, and the system did exactly as Papalangi said it would do if it DIDN'T have a head leak.

I had the car running hot, applied the pressure tester, and watched and waited.  And... nothing.  The gauge didn't budge.  Zero Pressure.  I kept it running, and nada.  I actually pumped some pressure into the system as I wanted to make sure I had a seal on the overflow tank.

So...  I hope that this means I can safely and entirely rule out a bad head gasket.  That grim spectre haunted my nights for two weeks!!!

Before I do anything else, I will wait for my new overflow cap and hose. 

But I am so happy about the system holding pressure and passing its head gasket leak test that I look like.... well, like this:  ;D

Thanks for the help.  I'm not out of the woods yet, as I'm still overheating.  But it sure feels good to rule out the worst possible culprit!  Hopefully, the fact that the system DOES hold pressure (but not too much pressure, as per Denis' great post explaining why compression leaks cause an increase in coolant system pressure) means that the heater core/servo area is not causing my problem.
Mike

Papalangi

Congratulations!

I well know that sigh of relief.

I was watching the water bubble in the overflow tank on my '83 Mazda 626 and thought "Gee, that's strange".  Then it blew the cap off the overflow tank and into my face.  A classic example of a blown head gasket.

The purpose of the pressure cap is to raise the boiling point of the coolant.  I forget the temp/PSI correlation but it raises the boiling point well above 212F and into the 220s.  A none releasing cap such as yours won't cause overheating.  At least not until a hose blows off.

Michael

PS, it's been awhile since I've read this thread all the way through.  Have you checked the timing and mixture.  Someone on the 250C mailing list just fixed his overheating problem by finding that the distributor had worked loose.
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8

kenny

Ahhh.  Information good.
So you have pressure integrity.  Even with that bad top hose. Not likely to be a head gasket. Your thermostat is new and tested.  radiator is supposed to be clean and fairly new. fan clutch is operating. Timing and mixture are possible as Michael points out, but I am still leaning towards the blockage/water pump scenario.

attacking this systematically.  Eliminating each possible cause.

Timing and mix are easy to check and can be fixed. Pump can be replaced.  A blockage may be undone with a good flush.  You are getting closer!

I have read that the only good flush is one that involves removal of the block plugs. These are hard to get at on a 6.9, being beneath the exhaust manifolds. I bet your engine has them similarly located.  relying solely on your radiator drain is probably not good enough and since you are going to flush it anyway, get your guys to do it by the book.

It's probably not your gauge by all the symptoms you have described, but while you're waiting for parts to arrive, find your temp sender that runs your temp gauge.  dirt means resistance and resistance will indicate high temps on the gauge.  clean the electrical connector and the pole sender that is screwed into the block.  put some dielectric grease on the pole.

you burped it with the cap off, right?  that's the only thing I would add to Styria's description of properly filling.  I additionally rev mine with the cap off and the front elevated slightly and the car up to temp to ensure the water pump is pushing lots of water throughout.

Hang in.

Let me ask you something else:  Does the temp go high and fail to recover a normal temperature regardless of driving condition?  For example, does it run to hot and fail to return to normal whether you are in stop and go versus freeway speeds?  does speeding up (and getting more air through the radiator) make no difference in the indicated temp?

How about your cooling fins. Clean?  Not bashed in?  How about the AC condensor.  Same Qs.  Does your Aux fan come on? 

Denis

Hi everyone

On the M116/117, there is a bolt that lies horizontally coming out of the cylindre block just ahead of the casting for the engine mount - remove each one and have water under pressure sent in each cylindre bank.

I would remove the radiator hoses and thermostat and push plenty of water in there - the more pressure the better. Even a loosely held garden hose might help.

Have fun  ;D

Denis

Paris, France

michaeld

Hi all,
I tell you what, I'm glad I've got 116-buddies like you all!  I've really appreciated your input.

I have to agree w/ Papalangi; a malfunctioning cap seems unlikely to cause dramatic overheating.  But - according to my Chilton manual's troubleshooting section - it was one more thing to consider.  For $10, I'm willing to give it a shot.

I ran one more pressure test since my last post as per the Chilton manual troubleshoot section: connect the pressure tester and pump the system to 14 lbs.  Start the car.  Check for any fluctuation in the gauge (which would indicate a bad head gasket).  There were no fluctuations.  I DID create a mess when I released the pressure and had some coolant burst out (which made Papalangi's version seem a LOT better).  But I wanted to rule out a compression leak as best as I possibly could.  GOSH AM I RELIEVED.

Kenny, I did check my timing.  It was slightly off, but by no more than a degree or two.  I figured that there was no way that little a diff could cause an overheat problem, so I didn't worry about it (I generally don't set my timing until after I've replaced plugs, condensor, and whatnot).

I'll re-read Styria's description of burping.  The procedure I'm following is: 1) have car on incline front end uphill; 2) turn on heater; 3) remove cap; 4) start car; 5) wait till it gets to operating temp, and/or thermostat opens; 6) pour in coolant slowly.  I don't know if it makes a difference if I shut the car down before or after putting the cap back on.

As for Kenny's suggestion that a good flush could solve my problem, something that I noticed following my wounded upper hose popping off gave me some food for thought: After I cleaned up the coolant mess, I noticed several white "globs" of residue on the floor directly under the water pump/hose connection that hadn't been there before.  There clearly seems to be "stuff" (politely watching my language here) floating around my cooling system.  It seems more like mineral deposits than anything else.  I would not be one iota surprised if some of this stuff has found its way into my water pump.

I will definitely flush the system before replacing the water pump, as I don't want my next pump KO'd by the same "stuff."  When I get this problem licked, I will also run a mixture of MBz coolant w/ distilled water.

I WILL look into my gauge.  Other than the gauge reading, I really haven't had any other symptom of overheating (no boiling, no steam, not even a loss of power).  I have been trying to shut the car down before such nastiness occurs, but it certainly is possible my gauge has been messing w/ my mind.

I'll make sure to ask how the shop intends to do my backflush.  If I remember, they mentioned disconnecting the radiator hoses, but I could be mistaken.  I agree that it's probably a better idea at this point to pay a little more to have the job done right.  I had a phone conversation w/ a MBz mechanic, who said that the block plugs were generally not something to mess with, as they could easily break when they were getting removed.  The MBz manual actually calls for them to be opened just to drain the system, much less a flush.

And (Kenny) to answer your last question: yes, if I'm driving on the road, and come to a stoplight, the car heats up at the light.  When I start driving again, the temp goes back down (just not as much as I would like!).  That's why I've pretty much been trusting the gauge.  Where should I measure the water temperature to verify the gauge's accuracy?

I won't enjoy replacing the water pump, but I believe it's w/in my "mechanic limitations" (I've replaced two water pumps, but both were simpler systems).  But I would SO MUCH rather be worrying over a water pump replacement than a head gasket replacement.  That relief alone makes the water pump seem like not such a problem!!!

As to your (Kenny) absolutely last Q's: (8 month old) rad core looks fine, w/ no sign of damage.  The fan blade looks fine.  The condensor looks decent.  The auxilliary fan (at idle) kind of starts to spin and then stops.  I haven't had the AC on at any time during or since the initial overheating incident.  Frankly, I'm not sure when the darned thing is supposed to come on except when the AC is on.

I was kind of mad at my car for putting me through all this, but I'm back to loving it again.  I can say it's never left me stranded through the whole affair, and I'm as proud of it for passing all its pressure tests as any parent displaying a "My child was student of the month at..." bumper sticker.
Mike

Papalangi

A thought occurs.

When you say it's over heating, what is the reading on the gauge?

I recently fiddled around with my aux fan as it didn't work and used a thermocouple to measure the temperature at the top hose to radiator connection by sticking it under the hose.  The temps matched at 175F and the aux fan came on at the unnumbered mark on the gauge, 202F at the radiator.  The aux fan switch is rated 212F.  If you are hovering around the unnumbered mark, you aren't overheating.

And now for something completely different.

Do the W116s use the radiator to cool the transmission like a domestic US car?  Or do they use a separate cooler.  Maybe the transmission is running hot and messing with you.

Michael
'83 300SD, I'm back!  It's the son's new car (12/2020)
1976 450SEL, 116.033  Sold it to buy a '97 Crown Vic.  Made sense at the time.
1971 250C, 114.023
1976 280C
1970 250/8

kenny

The aux fan should come on when the temp of the water gets high or when the freon pressure gets high.  The freon pressure switch is at the receiver/drier and is a double pigtail wire.  Jump these together with the car's ignition switch set to "on".  It should run.  Test the high temp switch, probably near the thermostat housing by grounding the single wire to the engine or another convenient ground.  Also with key in on position.  It should activate.

On my 6.9, I have a switch rigged into the cabin which effectively "jumps" the double wire at the drier.  I can control the aux fan in this manner.  In houston in summer (11 months) this gets used a lot and I view fans as consumable like batteries and tires.  On my 190, I just jump them at the drier and unhook the jumper in January.

If your car has been close to overheating, the aux fan should have come on.  If you can pull away from a stoplight and have the temp drop, that would seem to indicate that cooler water from the radiator is being pumped to the temp sensor.
That stuff floating around, if it is a mineral deposit, would be dissolved using a citric acid flush.
It is more likely to have stuck in a cooling passage in the block than to have mucked up your water pump.

Papalangi brings up an excellent point.  What are you seeing at the gauge when you say it's overheating?
The manual will say that the car can be operated when the needle reaches the red mark on the gauge, but that it should not be done for extended periods or similar language.  If your car runs to the gauge red line, but recovers to a lower temp, I really don't think that is overheating.  Higher temps than you would like to see, but not overheating.

Something else that occurs to me is that Mercedes temp gauges are not like domestic car temp gauges. MBs are more linear if that's the right word.  for example on other cars, the gauge will indicate cold and move through the gauge range to what is normal operating temp.  it will pretty much stay there with very little fluctuation. you have to beleive that stop and go driving and low airflow through the radiator situations will raise the temp, but the gauges don't seem to indicate it.  to me it seems like the gauge in a domestic car is like an idiot light, and you won't see temps above normal operating range until it is all the way overheated.  Not so with MB.  It shows all the fluctuations. Maybe there is a bit of that going on in your situation.

Papalangi scores again with good point about the trans.  If your car is like a 6.9, there IS a trans cooler tank at the bottom of the radiator.  If at a stoplight or at the point where the needle starts to rise, if you can put the car in neutral and rev a bit, not only will the pump move more water and the fan move more air, but the trans fluid will be cooled.

116.025

Quote from: Papalangi on 12 July 2006, 03:06 AM
Do the W116s use the radiator to cool the transmission like a domestic US car?  Or do they use a separate cooler.  Maybe the transmission is running hot and messing with you.

All 116s with AT have the transmission cooler in the bottom of the radiator, I believe.  Or I'll rephrase, all the 116s with AT that I've seen have had an AT cooler in the bottom of the radiator.  Heck, my 280SEL with a stick even had a radiator with connections for the AT cooler, but I'm sure the wasn't the radiator it rolled off of the assembly line with, and that since 116s weren't sold with anything other than the AT in the US, the PO was too lazy(or cheap, in which case I can't blame him) to get one without it.

Denis

Hi 116.025

I believe that you may have the original a radiator. Economies of  scale dictate that stocking only one model of radiator is a saving to Mercedes-Benz. Why manage a manual transmission radiator installation considering how few of these cars had manual gearboxes.

My own 0.02cts of and Euro's worth

Denis

Paris, France

Beautiful weather, greta place for a coffee in the evening - daylight stays until 22h15

michaeld

Papalangi, Kenny, 116.025, Denis,

Technically speaking, I am not overheating, and have never actually overheated (although the first night I DID get near redline).  The car has never "boiled over."  Generally, I have been able to shut the car down when the gauge reaches about 212F. 
However, this car - when the system is fully healthy - runs at 175F or lower during all the driving I do.  Something is wrong.  From my experience that first night, if I were to continue to run my car - particularly at slow speed or idle - I would redline.  Thank you, but no thank you; I do not want to overstress my engine unnecessarily.

Yes (as has already been revealed) I DO have a trans hose on the radiator.  I have read that a bad tranny can cause overheating.  BUT... I get hot idling in neutral, and my trans has no other symptoms.  It is not leaking, or slipping, or anything of the sort.  It is performing as it always has.  I'm not enough of a mechanic to go about making definitive statements, but I would be pretty shocked to find out that my problem is a bad tranny. 

While I have heard both sides on the fan clutch (that a bad clutch CAN and CANNOT cause overheating at freeway speeds) I am pretty convinced that the condenser fan can't create an overheat condition on the freeway.  But I am quite interested in (particularly Kenny's but also Papalangi's) advice on testing and using the condenser fan.

I received the new cap and spark plugs that I ordered, but have not yet received the radiator hose.  So  I haven't done any more testing of the system.  (Still breathing a sigh of relief over my system holding pressure!).

I intened to write a fully detailed post detailing my entire process (including the actual problem/diagnostic process/solution and the repair procedure) as I believe it to be a real act of service to document, record, and photograph every project, repair, and diagnosis for the forum.  My next step (after replacing the hose and cap, and burping the system) will be to have the system backflushed.  If that does not resolve my problem, I will be most likely be replacing my water pump.
Mike     

116.025

Quote from: Denis on 12 July 2006, 11:28 AM
Hi 116.025

I believe that you may have the original a radiator. Economies of  scale dictate that stocking only one model of radiator is a saving to Mercedes-Benz. Why manage a manual transmission radiator installation considering how few of these cars had manual gearboxes.

Denis, I understand your point completely, and would agree, except that my manual transmission 280SE has no place to attach the transmission lines, which was part of what influenced me to believe to radiator on the 280SEL was not the radiator installed in 1977.