Still overheating (grrrrr!)

[michaeld]

I'm not sure, but I MAY finally be zeroing in on what is causing me to run hot.

I took the car in and had a backflush done.  After the job, two the mechanics at the shop spent about twenty minutes looking at the system with the car running.  It got to about 212F (Assuming THAT is what the middle mark between the 175F and 250F indicates on the gauge) and remained there at idle.  They told me that that was within the normal/acceptable range; that the water pump was definitely pumping; that the  fan clutch was doing its job.  If anything, they said, the auxilliary/condenser fan was the issue.  I paid my $34USD (that's right; 34 bucks for a system flush; I couldn't wait to pay my money before they changed their minds!!!) and drove straight to the place that did my radiator core install.

The owner and another mechanic spent a little over twenty minutes looking over the system, letting it idle.  I did NOT tell them what the previous mechanics said.  They assured me the water pump was doing its job (if it wasn't, they said, I'd overheat in five minutes and there'd probably be a leak); the fan clutch was working; and - while the system seemed basically healthy - I might have a problem with my auxilliary fan.

Last week, I spent 10-15 minutes on the phone with the owner of MotorWerks - which seems to have a thriving business working on older Benzes - and got his best guess based on my description and steps taken thus far: Yep, the auxillary fan.  He told me that improper performance could even cause a car to run hot on the freeway.

I'm pretty happy: three opinions, plus a backflush, for $34.

I'm wondering if I had a bad thermostat, and failed to properly burp the system after the install.  At the same time, the auxilliary fan (or a component like the fan switch) was beginning to fail at the same time.

Now for my questions:
1) My auxilliary fan DOES come on; but... it doesn't seem to stay on very long; sometimes it starts to turn and then stops; it doesn't seem to come on when the car is getting hot at idle; I've had the A/C on the last two days, and pulled over and checked, and it wasn't spinning.  Does anyone have a clue when these infernal things are supposed to work?

2) I would like to begin by replacing the fan switch.  Is it mounted on the dryer - which is mounted over the condenser and located to the immediate right of the fan?  If so, my switch has two prongs.

3) Does an improperly functioning auxillary fan seem to explain my car's running at about 180-185F (maybe plus a couple of degrees) and idling at near 212F?

4) How hot does your car operate in city driving in hot weather?  (Keep in mind, I'm in Palm Springs; last week we got to 122F.  A COOL day in July/Auguse will run you 106 plus.

5) Does anyone know of a fan switch rated below 212F, and if installing one would be a bad idea?  I would be willing to trade a little power for cooler operation.

I'm actually wondering if I really have a problem, or if I'm just paranoid.  In any event, I would much rather mess with an auxilliary fan than with a water pump install.
Mike

[s class]

Michael,

What I'll say will closely second styria.

On my 280SE, the switch for the auxiliary fan switches in at 100degC, and then switches out again at 90degC.  In other words, the fan is supposed to come on when the car reaches 100degC, and stay on until it can manage to get the temp down to 90degC. 

I have found these switches to be problematic.  One I had only lasted a few weeks.  It seems that it suffers from the inductive kick of the fan as it turns on and off (for you electrical minded people).  I made a modification using a so-called fly-back diode to protect the switch.  This is standard electrical practice and I can explain it to anyone interested. 

My experience is that, as styria says, the fan at best can maintain the temp rather than bring it down.  What would normally happen in a hot South African summer is that if the temp gets to 100degC while stuck in traffic, the fan comes on and keeps it at 100degC until I can get to a clear stretch of road when the normal air movement helps to cool the engine, and the fan kicks out at 90degC.

The fans themselves can give hassles.  Its a kind of semi-exposed motor assembly, and the problems I found is that the brushes had worn out (similar to the problems you would have with an alternator).  Its quite easy to remove and disassemble the fan motor to see what's happening.

THe symptoms of a failing fan motor are that it may or may not work when its supposed to, and when it does run it may turn weakly.  When the fan is good, it is POWERFUL.  Even in the car you will hear it as a roar from the front end. 

The fan is easy to check.  Disconnect its terminals and wire it directly to the battery.  Don't try this with the fan out and in your hands because if all is well it is powerful with quite a recoil when it starts. 

My opinion is that the auxiliary fan is just that - a backup - 280SE's supplied here without aircon do not have the fan.  Even my 450SL with aircon does not have the extra fan.  These cars can maintain and regultate their temps without the need of a fan.  My suggestion to you is to get the fan working as a safety measure, but then try to get the cooling system properly sorted to the point that the fan seldom needs to come on.  I'm sorry, because I know that isn't a very helpful comment right now, given how much effort you have devoted to trying to do just that. 

I hope yo do soon win through though.

Ryan in South Africa.

[macatron]

Hi Michael,

I have a 1977 280SE and I live in south Orange County.  My car seems to behave almost exactly as yours does.  At idle, my car's temp will creep up to 212F (that mid-mark on the gauge).  On particularly hot days, the needle will move slightly above that mark.  On those same days (when ambient temp. is in the mid-90s), the temp will usually drop to around 180-185F while freeway cruising (70 mph) for an extended period of 10 minutes or more.  The fact that my car will more or less hold the 212F mark means to me that the fan is working as it should and that the water pump is working as it should.  I have yet to observe a leak and have no reason to suspect negligent maintenance (previous owner was very good about taking the car for regular maintenance to a Mercedes new-car dealer).

Either our cars have had identical failures or this may be normal.  I'm not sure.  I do know that money permitting, I will take my car in for a thorough check of the cooling and air conditioning systems sometime in the next couple of months.  I know this isn't exactly a helpful post but perhaps by comparing our cars, we may both be able to benefit.  And, I can share with you my mechanic's diagnosis as soon as I have it.

Best regards,

Mike Shea

[michaeld]

I know this isn't exactly a helpful post but perhaps by comparing our cars, we may both be able to benefit.  And, I can share with you my mechanic's diagnosis as soon as I have it.

Macatron, S Class, Styria, and all,

I begin by quoting Macatron because his sentiment is exactly what makes these forums so worthwhile: mutual support and sharing of knowledge for the benefit of everyone.  (And by the way, Macatron, the mechs who looked over my car began by saying that this was within normal for these older cars and wasn't a problem.  For my part, I'd like to get mine back to running as cool as possible, time and money permitting.).

Styria (and S Class),
I'm not going to say that I've got my problem licked until, well, I lick my problem.  Having several mechanics tell you the same thing means having a good starting point.  I will replace my fan switch, see what happens; if that doesn't work, I will replace/repair the fan, and see what happens.  If you had asked me about fan clutches and aux fans prior to all of this, I would have told you that I did not believe that a bad fan could be responsible for a freeway overheat.  But I've now had half a dozen mechanics, including a few Mercedes mechs, who have assured me that one could.  At this point, I would be willing to believe anything that works!

Actually, what you are both saying may be my problem.  I've never actually overheated at any time; I've just run hotter than I should have.  I'm wondering if I DID have a bad thermostat, replaced it, but then didn't burp properly.  I now know how to burp (both myself and my car ) properly, and the car doesn't seem to be getting way hot like it was.  But it is still running a little hot.

I have also noted that operation of the fan at best holds the temperature steady-it prevents it from climbing too high rather than bring it down. I realize that what I am saying flies in the face of what you have been told, but I can only convey to you the way I see it.Regards, Styria

Styria,
I appreciate your "I calls it as I sees it" attitude and value your superior mechanical knowledge.
Actually, we may just be discussing semantics.  I can tell you this: After my car had remained at 212F for a good ten minutes plus, the shop owner got in an hit the accelerator for a couple minutes.  The aux fan (which had NOT come on up to that time) suddenly kicked on.  He called me over (I had been watching for the aux fan to come on, and occasionally coming over to look at the temp gauge) and showed me the temp: it had come down a good 20 degrees F almost immediately when the aux fan came on.  The owner suggested I might just want to wire the fan to come on all the time.  I wasn't so keen on that, but I would sure like it to come on when it is needed.  It seems to me that the fan has the capability of keeping the engine temp down, and it also can lower the temp by 20F or so.  That may be all I (and Macatron) need to keep cool.  What do you think?

I have found these switches to be problematic.  One I had only lasted a few weeks.  It seems that it suffers from the inductive kick of the fan as it turns on and off (for you electrical minded people).  I made a modification using a so-called fly-back diode to protect the switch.  This is standard electrical practice and I can explain it to anyone interested.

S Class, Yes, please, I would very much appreciate knowing how you improved the fan and protected the fan switch.  As for the condition of my fan, I'm not so sure the "battery test" would tell  me much: the aux fan DOES come on, and come on powerfully, but I'm not so sure that it is coming on when it should, OR that it is staying on for as long as it should.  I wouldn't mind having a switch that came on at about 200F (93C), barring S Class's warnings about the fan's problems.

I will of course post back once I've installed a new fan switch and tell you what happend.

P.S. I also wonder if the fan clutch (or even the water pump?) could be failing slowly.  Do these units just up and go bad, or can there be a gradual failure?  The mechs said they were POSITIVE the water pump was working, and they were also sure the fan clutch was working.  But they were just using their hands to see if it was blowing back into the engine (i.e. they didn't do any other tests).  I have put a rag into the fan blade path, and it does forcefully spin the blades thru the resistance.

[kenny]

 I can tell you this: After my car had remained at 212F for a good ten minutes plus, the shop owner got in an hit the accelerator for a couple minutes.  The aux fan (which had NOT come on up to that time) suddenly kicked on.  He called me over (I had been watching for the aux fan to come on, and occasionally coming over to look at the temp gauge) and showed me the temp: it had come down a good 20 degrees F almost immediately when the aux fan came on.


Michael:  You may be giving too much credit to the aux fan here since by revving the engine, your mechanic was not only causing the water pump to move more water, but the viscous fan is also drawing more air through the radiator.  I won't argue that the aux fan didn't have some contribution to the lowering of the temp, though.  I have a switch rigged into the cabin of the 6.9 that I can turn the fan on with when in traffic in the heat.  I have a 1990 190 E that has the fans on all the time as they run even hotter than the older MBs.  I jumpered the pigtail at the dryer. To me in the heat we have here, if I have to replace a fan every couple of years, so be it.

[Papalangi]

Michael,

Rather than jumpering the switch or putting a switch on the dash, consider using a fixed or adjustable fan controller like these,
http://store.summitracing.com/egnsearch.asp?N=700+115+%2D106362&D=%2D106362

You can wire it in parallel with the AC drier temp switch or directly to the battery which will allow the fan to run after you have parked to help with any hot start issues you may or may not have...

A different Michael

[michaeld]

Michael:  You may be giving too much credit to the aux fan here since by revving the engine, your mechanic was not only causing the water pump to move more water, but the viscous fan is also drawing more air through the radiator.  I won't argue that the aux fan didn't have some contribution to the lowering of the temp, though.

Kenny,
Of course, you are totally correct; I should have thought of that when I wrote the post.  Let us then say at least that the aux fan has SOME limited capability of providing a quick "cool down" of an engine in addition to its primary role (as per Styria and S Class' contribution) of preventing the engine from getting overly hot in the first place.

I think it also needs to be said that none of the mechanics who looked at the car really and truly delved into it.  They just looked, listened, and felt hoses.  Their conclusions could have been incorrect due to insufficient information.  But, again, its a place to start...

Now, if my aux fan IS operating (and it is, as I've seen it come on several times and spin forcefully) does that mean that the motor is O.K., or could there still be a problem?  It's a bit strange: I've driven the car, parked, and then returned an hour later, and I could hear the aux fan kick on at startup.  But then I've also driven with the air on, parked and got out of the car (A/C still on), and the fan was not operating.  I've also seen the fan begin to spin, and then quit.  Also, my gauge has read over 212F and the fan was not kicking on (though that could be due to an imperfect gauge).

Papalangi,
Thanks for that link.  I may consider this in the near future.  What I'd like to begin with is to simply have everything pretty much as God and his MBz engineers intended and see what that does.  But I DO want to run cooler, as it seems to me that the hotter I run, the shorter the life of the engine and the less I can trust the car.  BTW, Michaeld and MichaelP?  I STILL think we Michaels can take over the world; all we need is the right plan, implemented at the right time...

Also, I am now noticing (and this was NOT the case until after I drained the radiator to replace the thermostat after initially getting hot) that I have to add coolant to the "full" mark.  This was happening before and after I did the pressure test.  I performed 3 versions of the test:
1) I connected the tester to the overflow tank, pumped it to 14psi, and then waited.  The manual said to wait 2 minutes, and there was absolutely no drop in pressure.  I waited for a total of six minutes, and saw an insignificant drop that could have been w/in the margin of error for the tester gauge.
2) I started the car, let it get to operating temp, and connected the tester, looking to see if the pressure increased dramatically (due to the higher pressure of the engine oiling system).  It did not increase at all.
3) I connected the tester, started the car, and allowed it to run, checking to see if the pressure fluctuated (due to the fact that a cracked head gasket usually appears at one cylinder which would cause the pressure to jump as the engine rotated).  It did not fluctuate at all.

Question: should I still do a block test?  I would have to buy one.  I would have paid the place that did my backflush to do it, but the mech said I didn't need to (and I like a mechanic who passes the opportunity to make some money).  The night I first overheated, I did not lose any coolant; nor did I lose any coolant for a couple of weeks doing short drives until after I replaced the thermostat and refilled the system.  Since then, I've had to add a number of times.  Are there compartments in the block that the coolant isn't reaching, or is the coolant going somewhere it shouldn't?  It does NOT seem to be getting into my engine oil.  Could it be getting into the exhaust?  I have no white steam at the exhaust.  I have also repeatedly felt my interior carpets, and no sign of dampness or smell of coolant.
I have a leak finder kit that uses special dyes and goggles.  I guess I can try that out.  But there are no apparent leaks or puddles, even after the car has been sitting and idling for half an hour.
Mike 

[michaeld]

Papalangi and S Class,
I just went to Papalangi's link.  These are switches designed to restrict the on/off operating of the aux fans to various predetermined temp ranges, and also provide spike protection.  This actually seems like a pretty good idea.

[michaeld]

Here's an update:

I purchased and installed a new 212F aux fan switch; but no change in the status.

Recall, I was given a clean bill of "cooling system-health" by two radiator shops.  I may be okay.  But it does seem to me that I am idling hotter than I did before all this started (that's what's driving me crazy: it "seems" like...; I wish I had actually written down the info that my temp gauge was giving me under varying conditions, as I just don't remember clearly WHAT the gauge was showing.  Call that a word for the wise.).

I have new spark plugs, and so will do a compression test to check for anything hinky there.  I have not yet done a block test/aka compression leak test, but have been loathe thus far to spend $45 for the kit.  I may not know for sure whether I have a problem until I make another 50 + mile drive.  For the time being, the system seems to be doing its job in the 105F + conditions of Palm Springs.

[kenny]

You did clean the temp sensor sender didn't you?

[michaeld]

You did clean the temp sensor sender didn't you?

A question asked in the above manner is somewhat identical to the parallel form, "You're not an idiot, are you?"

Kenny, the answer to your question - and, sadly, the one I posed as well - is 'no.'  I'm not sure where the temp sensor is.  I presume you are essentially asking the question, "Are you sure your temp gauge is working correctly?"  I have a non-contact thermometer, but don't know where to "stick it" (and would not appreciate any ideas that involve any locations other than my car!) to get an accurate comparison.  My system has never boiled over.

I did clean the wire female terminal that connects to the fan switch when I installed the new switch, but nowhere else.  Where would this temp sensor sender be?  Unfortunately, I haven't yet found a detailed description of cooling system components in any of the sources I've consulted.  My Nissan 200SX Chilton manual told me where everything was; same same for the shop manuals for my Ford Galaxie.  Thus far (and this includes the CD version on the site) I've been pretty amazed at the lack of detail for Mercedes service manuals.

[kenny]

You seem to be concerned with you apparent temp and I am trying to suggest that maybe the guage is inaccurate.  At the rear of the head on the right hand (US passenger side) is a single pole sensor in the engine.  There is an electrical single wire connector hooked to it. The electrical business is a part of your CIS wiring harness.  The other parts of the harness go to the 212 switch, the fuel cutoof switch, the warm up regulator and the the cold start switch.  That should help you locate it if it is similar to 6.9.

In the near vicinity of the temp sender is a two-pole for the thermo time switch.  Not a bad idea to clean it while you are at it.  Get some aerosol electrical parts cleaner or carb cleaner or your solvent of preference and clean the poles and clean the electrical contacts inside the plugs.

Carb cleaner will put out your cigarette in a dramatic fashion so please be careful.

I think most will measure their temp at the thermostat housing for general information, but I think you should shoot the temp sender for a direct comparison of real versus gauge measured temps.

What I am getting at, and believe me I am in no position to imply idiocy, and I regret that your inferred that, is that all your perception of this "problem" is being fed by the temp guage.  If it is way off, you are working under false assumptions about the rest of what is needed.

I think you have gotten a lot of really helpful responses from the board. Taking them in order is important and I think the gauge issue is fundamental.

Here's a picture of what you should be looking for.  The hole in the head is where the two pole termo time switch goes.  To the left is the single pole sender for the gauge.  It's a tight fit against the firewall.

[michaeld]

Kenny,

Thanks for the pic and the description; I'll take a gander at mine and give the sensor a good cleaning.  If it looks nasty I'll replace it.

Please don't think you offended my sensibilities; I was just making an attempt at humor.  Sadly, it turns out that all too often when someone asks, "You did (blank), didn't you?" it turns out that I didn't (blank)... and frankly, I was often sort of a dummy for not doing (blank). 

It certainly is a possibility that I my gauge has been "lying" to me, as my system has never boiled over or steamed up.

In terms of "shooting" the sensor area w/ my infared thermometer, would the outside engine temp be about the same as the inside engine temp that the sensor is measuring?

[Papalangi]

Hey Michael,

For reference, here is what my '76 450SEL did yesterday.

Outside temp between 78-80F, gentle cruise around town checking the PO Box and getting tacos at Taco Time.  Speeds around 35-40MPH.

Took usual long time to reach 175F, sometimes it never reaches 175F even on I5.  At the Post Office, it was finally just above 175.  During 1.5 mile cruise to taco store, it drifted up to a bit below the unnumbered mark.  At the taco store, it drifted higher, I turned the radio off to listen for the electric fan.  It came on just as the needle cleared the mark.  Temp drifted up slower and topped out with a bit more than a needle's width black between needle and mark.  This was about 8 minutes or so.  Once out on the road again, it came back down to the unnumbered mark and mostly stayed there for the 5 mile trip home.

It does this about 3-4 times a month but more usually stays right around 175.  I can do the 9 mile commute to work and never get above 175 even when it's 80 outside.

As for the infrared temp gun, the sensing area is cone shaped and at 1 foot could be as large as 1.5 inches.  You need to get within six inches or so if you are shooting at the temp sensor to get an idea of the temp in that area.  I think it would be more important to be consistant in your measurment than where you take it.  Personally, I would shoot for the top radiator hose connection and factor in a 10F drop.  That's based on my using a thermocouple type instrument and placing the thermocouple under the edge of the hose and comparing it to my gauge.

Hope this helps,
Michael McDuffie
Papalangi means white man in Tongan

[kenny]

In terms of "shooting" the sensor area w/ my infared thermometer, would the outside engine temp be about the same as the inside engine temp that the sensor is measuring?
[/quote]

I doubt the outside would be as high as the coolant temp.  What I would look for is a large variance of readings between the gauge and the temp sensor reading from your hand held.  Even though different, do they rise at the same rate?  Do they parallel each other or does the guage outpace the laser as temp rises?