Could a brake booster vacuum leak cause an overheat?

[Brian Crump]

Back to basics. How do you know it is running hot?
What is telling you it is hot?
What is the ambient temperature?
Regards,
BC

[michaeld]

Brain,

Well, you see, I once had this dream and Yoda said to me, "HOT you are running, yeeesss."

Actually, I replaced the gauge with a Sunpro aftermarket (at least for the time being; dang I hate looking at that thing!).

I'm not sure exactly how to read the gauge (and I've forgotten two days in a row to call their tech support and ask) as the display is not nearly so "matter of fact" as our 116 temp gauge.  But I know its reading hotter (this the second gauge that has done so) than I would like to see.

I'm in Palm Springs, CA, and the heat can be HOT.  But the ambient temp doesn't really seem to be a major factor (it might happen a little faster when the temp is real hot, but not that much).  We've been in the 80-90s F recently.

What is telling me it's hot?  Beyond the gauge, not too much (the car accelerates and runs fine, the water level is good, no boiling over).  Some time back I blew my ACC servo, and lost a LOT of coolant fast.  Then I seemed to have trouble with leaking at the bypass location where I joined the hoses (I hope I have that fixed now; we'll see).

I am one who looks forward to NOT having to look at my temp gauge!

[Brian Crump]

What I am getting at is simple. Is your car really running hot?

Does it smell hot? Does it feel hot? Has the paint peeled off your bonnet?
Is the gauge correct? Have you connected a master gauge to compare?

How hot is hot?
My 450 runs at a constant 90C (indicated) and on a hot day, between 35 to 40C will nudge over 100C(indicated) without overheating.

Have you investigated the join you made?

Maybe your car is overheating; maybe you are worrying about nothing.
I recommend you give Yoda (Yoda who?) the sack.
BC

[michaeld]

Does it smell hot? Does it feel hot? Has the paint peeled off your bonnet?
Is the gauge correct? Have you connected a master gauge to compare?

I'll try to answer: No, not really, yes, I think so, and yes (I connected a second gauge, which seems accurate).  I DO have some peeling on the hood, but I bought the car that way, and it still doesn't have a hood cover (or whatever that asbestos-looking insulation is).

If my temp stopped at 212F (100C) I wouldn't be complaining.  If you were looking at 110C how would you feel then?  Especially if it wasn't a hot day and you didn't have your air on?  Maybe you'd be paranoid like me?

I initially wired the gauge in the engine bay ('twas easier) and just recently moved it into the passenger compartment (because I got tired of being freaked out asking, "Am I overheating?  I think I might be overheating...").

I've also had that servo blow up, and then after that I had the bypass joint blow up (I may have caused that latter issue by overtightening a plastic POS Autozone splicer; I now have 2 actual-genuine metal splicers that I hope will keep that servo-bypass area from giving me problems). 

I've got a clean bill from the mech, but that gauge is climbing more than I'd like.

If it fails smog due to high NOx, I'll kinda figure that its because of running too hot.  If it passes, I'll kind of get into a less paranoid mode again and start driving my 116 only on shorter drives while I look things over.

But I've got to take my smog by May 16, and that aint too far off.  Can't NOT worry.  At the same time, I'm also worried (I frankly don't know the laws that well) that if I DO fail my smog test - especially badly - I'll get lumped into some heinous "gross polluter" category and REALLY suffer.

So you see my issues?  On the one hand, I've got to drive long distances from home to bring out the hot running issue; but on the other hand, I'm afraid to drive long distances from home and have big problems.  At the same time, I'm a little worried about what will happen if I AM running hot during my smog test, yet I've got to take that test soon.

And you wonder why I'm paranoid?  They really ARE after me, Brian!

But I'll go ahead and fire Yoda, as per your advice.  I couldn't understand him half the time anyway, and he WAS old, short, bald, handicapped, and generally unattractive.

[Brian Crump]

It's OK.
If the paint had peeled from extreme engine heat your oil would have boiled as long time ago.
Paint will peel on the bonnet for a variety of reasons - one being the lack of under bonnet insulation.
Look - either it will boil or it won't. Either it will pass the smog test or fail. Stop worrying.
The only time my gauge headed for 110C was when the electric fan switch had burned out and the fan failed to come in.
I assume your electric fan works from what you have said.
So, in essence either stop worrying and wait for it to blow up (if it does) or go to a reputable radiator repairer and let them diagnose any issues.
Have you had your thermostat checked? I'm sure you said you had. A faulty thermostat would be the most likely cause of overheating if everything else is OK.
Regards,
BC
PS - they are not after you - there is NO-ONE out there

[zeppelinboy]

Another possibility of having a condition where you can idle forever and have good temps but then expeience higher than desired temperatures under load is a head gasket failure. It is possible to fail in such a way as to allow exhaust to escape into the cooling system causing higher than normal temps, but still not contaminate oil and water. I had a LT1 engine fail exactly like this and it took forever to find the culprit. A high pressure leak down test may help you find bubbles in your coolant.

[500eguy]

lets hope it isn't a head gasket problem for you! i would def. check for head gasket...  if everything else works than that could most likely be the culprit... good luck and hopefully you are just to worried about it.

[michaeld]

Brain,
As per your last sentence ("there is no one out there"), you just clearly don't see eye-to-eye with FBI Special Agent Fox Moulder, do you?

Zeppelinboy,
I've been paranoid about that ever since I read about it on the web.  But the mechs I've had the car in to say a head gasket isn't my problem (though I haven't had a leak down test done.  I've been told a lot of old cars that actually don't have any overheat problems at all will often still have SOME leak).

BTW,
I did a compression test this evening (I got 160 PSI across the board, with two cylinders reading 165 and 167; 160 psi = 1100 kPa).  Certainly not low compression, nor did I have two opposing cylinders out of whack in any way that would be an indicator of a head gasket issue.

I looked at the old plugs.  They were all in the normal range, I'd say.  If anything, all I saw out of the ordinary was a little carbon deposit on the top of the thread; but the electrodes and insulators all appeared perfectly normal.  There's no tell-tale sign there.

I also checked out Tomi's "measuring plate" idea (I call it a "throttle valve plate," but he's probably right), and the corresponding piston is fine.

Tomorrow is a busy day, but Thursday I ought to be able to look at the timing and disconnect the brake booster vac line to at least eliminate the bad booster as a possible culprit.

[Brian Crump]

Brain,
As per your last sentence ("there is no one out there"), you just clearly don't see eye-to-eye with FBI Special Agent Fox Moulder, do you?

You are correct, but then, I am not a great fan of popular culture and do not own a television set.
I doubt you have a head gasket issue.
I fail to see the relevance of the brake booster.
In the absence of hard data I doubt you have a real problem - and I hope I am correct. It does occur to me that you may have a stray electrical charge affecting accuracy of your temperature gauge. Such a prolonged spike might occur if you have a bad earth or faulty alternator/voltage regulator.
You can definitively test the temperature with a master probe. That is the route I would take.
Good luck.
Regards,
BC

[michaeld]

Brian,
You are wise indeed for not contaminating your mind with television.  I've cut way down on mine as well in favor of reading.

You mentioned the "master probe" once before, and I forgot to bring it up.  What is that?  I've never heard of a "master probe" (maybe because I, after all, am a slave and they just don't tell us about "master" stuff!).  I'd love to have an accurate way to check my system.

You mentioned "stray electrical charges."  That's interesting too.  I KNOW I've had some grounding issues (e.g. some times a window or the radio/antenna won't work, then they will).  So, having experienced a couple of electrical gremlins, I certainly view this as a possibility.

I had a stupid idea occur to me that is probably totally lame.  But the talk of a "fuel issue" got me thinking: Shortly prior to having all my issues, I bought a locking gas cap and installed it.  Is it possible that that aftermarket sucker could have improperly sealed and resulted in gradually overheating (over 35-45 min)?  I put my old OEM unit back on just in case (and now my w116 is a garge queen, so no worries about fuel-filchers).

I put new spark plugs in following my compression test, having taken extra time to do housecleaning on my cylinder heads and valve covers.  I haven't driven the car since the compression test, but will drive it tomorrow or Saturday.  Tomorrow I play to change the fuel filter and replenish the rear axle fluid, and the next day I plan to change my engine oil and tranny fluid/filters.  I'll check my timing sometime during that period.

As a PS, has anyone ever cleaned their EGR valve?  I'd be interested in that process.

PPS, I'd also be interested in cleaning the throttle body.  Mine actually looks pretty clean, but there are a very few oily streaks in the assembly.  I frankly don't even know what constitutes a "dirty" throttle body.

PPS, Did the 77 US 450SELs have an oxygen sensor?  I bought one online (mercedes-benz-parts-direct and many other online parts sellers LIST A NUMBER for oxygen sensors), and now I'm wondering if I got stuck with the darned thing that doesn't even apply to my car.

[Brian Crump]

I had a stupid idea occur to me that is probably totally lame.  But the talk of a "fuel issue" got me thinking: Shortly prior to having all my issues, I bought a locking gas cap and installed it.  Is it possible that that aftermarket sucker could have improperly sealed and resulted in gradually overheating (over 35-45 min)?  I put my old OEM unit back on just in case (and now my w116 is a garge queen, so no worries about fuel-filchers).

No.
A master gauge is a probe used by a mechanic to test the temperature at certain areas - eg; top of the tank or at particular hoses. Usually it is  rated scientific - that is, it has a known degree of tolerance - and thus is more accurate than a gauge which may be suffering old age. Its power supply is independent of the car. For example, I had a Lancia where as the revs increased, the electric oil pressure gauge read lower and lower. Connecting the oil line direct to a master gauge showed good pressure. The fault lay with the gauge...
Regards,
BC

[michaeld]

Back again.

thought I'd tie up whatever loose ends there were here.

I replaced my fuel filter (and it was a pain to disentangle the filter from the rest of the fuel assembly) and took the car for a drive to make sure no leaks.  Yay!  Didn't see any.

Then I decided to try to settle the issue of "brake booster-induced overheating" once and for all.  I disconnected the booster line and attempted to seal it with a combination of tape and a balloon, and then more tape.

Assuming I sealed the line properly, the booster had NO EFFECT on the temp.  Dagnabbit!  In spite of the poo-poohing some of you gave my idea, I WAS STILL HOPING!

I also discovered that my booster is basically just an ugly brown thing: I lost virtually NOTHING regarding brake pedal action by disconnnecting it!

Assuming I get through my smog okay, I'll turn my attention on the booster next anyway.  It wasn't much of a problem until I got my Pontiac, which has sensitive power brakes: now I go from one car to the other, and I'm either face into widshield, or wondering why I'm not stopping...

[Brian Crump]

I also discovered that my booster is basically just an ugly brown thing: I lost virtually NOTHING regarding brake pedal action by disconnnecting it!

Yeah well, I'm having some trouble believing you can stop the car without the booster working....unless you are related to the Californian Governor?
Regards,
BC

[michaeld]

YA ALLA BUNCHA GIRLIE MANS!!!

I'm a weightlifter, and while my midsection no longer looks as good in a tu tu as it used to, I've never lacked in the strength department.  I haven't had any troubles braking, and the car actually brakes fine (other than the "push down hard" part).  I'm 6'2" and about 285, for what it's worth.

If I have to do a LOT of braking (stop and go traffic), the ball of my foot will get a little bit sore from pushing down on the pedal, but that's it.

It's funny you mention the Governator.  I actually met him while working out in a Gold's Gym (this a few years before he became governor).  It turned out we were both doing back and biceps, and so we essentially worked out together!  At first he was quiet and somewhat standoffish, but once he became aware that I wasn't a "starstruck" fan, he was a normal and actually pretty funny guy.  I was actually a fair bit more muscular than he at the time, believe it or not.  I think he was just starting to train for a movie role, and he clearly hadn't been lifting heavy.  His calves were still enormous, but the rest of his body needed "to get pumped up!"

I had previously presumed that I was getting at least SOME boost from my booster; but disconnecting the line has proven that I haven't been.

Anyone want to go on a scenic drive with me down a nice steep mountainside?

[Brian Crump]

I had previously presumed that I was getting at least SOME boost from my booster; but disconnecting the line has proven that I haven't been.

My advice, and I meant it in all seriousness - get your car to a qualified, certified, licenced machanic without delay.

It is a danger to you and the rest of the driving public you meet.

Regards,
BC