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Over-pressurizing Cooling System. Head/Headgasket?

27K views 89 replies 20 participants last post by  Bali 
#1 ·
University life is keeping me from checking the forum regularly..I haven't been here for a while. I hope you guys were able to winterize your babies before weather got cold.

So, I have been trying to solve the cooling system issue, I'll try to make it short since it's a long story.

Series of problems was initially started by a cracked expansion tank. It was cracked wide open while driving on highway, overheated engine for few minutes. Needle had stayed at red-zone for minutes until I pulled over to safe area.

Few weeks after that, car started to show the symptoms of stuck-closed thermostat. Symptoms consisted of stuck-closed thermostat because 1) overheating while driving, 2) hot and tight upper hose and cold lower hose, 3) excessive steam coming out of bleeding screw when warmed up.
At first I thought the problem was caused by improperly bled system, but turns out that thermostat was completely stuck closed. I finally took it apart, and put it in the boiling water, did not move a bit. So I requested a replacement thermostat from Oreilly's, they gave me a new one.

But a new thermostat did not solve the problem. Car still overheated and showed the 3 symptoms above. I decided to put an old thermostat housing without thermostat, but my effort did not see the light. Car currently does not have thermostat, but still overheats.

That's why I was beginning to think that cylinder head or head gasket might have been blown. Shop guys thought so, too. So we performed combustion leak test, but the blue testing fluid did not turn into yellow color. I haven't performed a cylinder compression test, nor did I do leak-down test. (I can only think of those three tests for head/head gasket diagnosis..)

But I found an interesting thing today. The driver's side upper radiator was pretty hot (160F), but other parts of radiator were cold (90-100F). Could this mean that radiator is somehow clogged? It's only 2 years old, but it's possible because it's the only part I haven't checked thoroughly.


Let me summarize in few bulletin points.

**Currently, the cooling system has..
  • No leak at all. System is holding the pressure nicely.
  • Water pump, 1.5 years old, Oreilly part. Impeller is solid and not spinning freely.
  • Radiator, 2 years old, Oreilly part.
  • Radiator hoses, 2 years old, OE part. Lower is bit covered by leaked motor oil, but they both are in good shape.
  • Thermostat, new, not defective, Oreilly part. Even with the new one, car still overheats, thus the engine currently has empty housing.

**Symptoms shown so far.
  • Engine is running fine, RPM is very stable when warmed up. No milkshake oil, no white smoke coming out of exhaust, no definite signs of blown head/head gasket.
  • Engine shows symptoms of stuck-closed thermostat, though it is currently not installed in the engine.
  • Upper hose is hot and excessively pressurized(rock hard), but lower hose is just little warm(w/o thermostat).
  • Driver's side upper radiator is quite hot (160F), but driver's side lower, middle upper&lower, passenger's side upper&lower radiator are relatively cold (90-100F)
  • Combustion leak test shows there is no exhaust gas present in cooling system. Blue testing fluid does not change. (Have not done leak-down test, compression test)


According to the symptoms shown so far, do you think the head is blown? Or do you think the radiator is somehow clogged and over pressurized the system?

I know it's a such lengthy-unorganized thread, but please take a minute and lighten up my dark path ahead. I'm totally lost right now..
Thanks in advance! :hi:
 
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#2 · (Edited)
cracked head, or combustion pressures leaking past the headgasket.



if it pressurizes the system, ALL THE HOSES ARE HARD.


is that the case?
 
#4 ·
cracked head, or combustion pressures leaking past the headgasket.

if it pressurizes the system, ALL THE HOSES ARE HARD.

is that the case?
I didn't know that fact. I only checked the upper hose, it was pretty hot and rock hard. But the lower hose wasn't, it was only little warm. I guess I got lucky!


Having dealt with this, yes. The pressure should be even throughout the entire system, and if it was that bad, you wouldn't need a combustion test--you'd be able to smell it in the coolant.

Sounds like a clogged radiator to me. Should've bought the Behr? You can remove it and run a garden hose through it (oh, the horror) to test.
Maybe I should've bought the Behr. A friend of mine knows a radiator supplier, he gave me one for $60. Turns out it was Murray, same brand as Oreilly ones..$70 less was very tempting for a college student who just paid four figures of college tuition lol.

So, clogged 2 years old radiator seems quite impossible, especially when it's had plenty of fresh coolant and water ever since the ET blew..But I guess it really is the clogged radiator causing this mess, still wondering why though.




I'll be replacing radiator tomorrow, I'll keep it posted. Thanks guys
 
#3 ·
Having dealt with this, yes. The pressure should be even throughout the entire system, and if it was that bad, you wouldn't need a combustion test--you'd be able to smell it in the coolant.

Sounds like a clogged radiator to me. Should've bought the Behr? You can remove it and run a garden hose through it (oh, the horror) to test.
 
#6 ·
Well, did replace the radiator with Behr one, thermostat seemed to be in good working order, so I didn't really bother to buy Wahler one.

After replacing radiator, I performed a good bleeding procedure for 15-20 minutes. I let the engine running til the air doesn't come out of the bleeding port, seemed to be bled properly. Heater wasn't blowing hot air and there wasn't any water in heater hose, so I unhooked the heater hose from heater valve and blew several short burst of air with an air blower gun. Good amount of trapped air came out through expansion tank, heater is working fine now.

Nevertheless, problem still exists. Upper hose is hard and hot, lower hose is hard and cool. Meaning that thermostat is working fine..
After 10 minutes of test driving, coolant overflows, then overheats while idling. Both fans are doing their job brilliantly, as lower hose and lower part of radiator are very cool.

Judging by the evidence of good amount of trapped air in heater system, do you think the air is still trapped in water jacket?
Or since the car is not showing any evidence of cracked/blown head/HG, should I suspect a warped cylinder head? It seems extremely hard to believe, because as far as I know, engine block and HG blows first before the head gets warped almost every time due to the excessive heat.

My next plan is to blow air through the engine block return hose, but I'm not even convinced that air could be trapped in the WATER JACKET.
oh man I really am lost.
 
#7 ·
It doesn't sound like air, but a physical blockage. And no, a warped head exhibits the same symptoms as a blown head gasket (any head sealing issue does).

When you bled, did you have the heater on high? If you couldn't get air out without compressed air, I'm wondering if the heater valve itself may be stuck and blocking flow through the system somehow.
 
#9 ·
Thanks for your attention again, guys.



That's what I thought..Car's not exhibiting any symptoms of blown HG/block. I was thinking that maybe the white residue on every part of cooling system has somehow interrupted cooling capability, caused overheat. So, what is that white residue on cooling system, anyway?

Oh and yeah, bleeding procedure was done while heater was on full blast, which didn't really help. So, are you suspecting that the water already in the heater system gets overflowed through the expansion tank, because of malfunctioning heater valve interrupting the flow? Maybe it's possible when it gets stuck after allowing good amount of water to enter the heater system, and then prohibiting it from fully circulating. (I don't know if that makes perfect sense, hope you understand my poor English.)


You got a stuck thermostat. Replace the damn thing. You can't cheap out on stuff like this.
That's what I had suspected at the first time way before I replaced the radiator. Putting a new one didn't really help, so I put an empty thermostat housing, which didn't help either.
Judging by the exhibited contrasting evidence of stuck-closed thermostat (i.e. cool, but hard lower hose-The weather was fairly cool today, so I assumed it should be cool and hard. Did I get this right?-, no overheat upon acceleration/driving, etc), do you think I have a faulty T-stat again? Air bubbles were coming off the center of thermostat housing when I put it in the hot water(not boiling, but hot enough), thus I thought it's safe to install.
 
#8 ·
You got a stuck thermostat. Replace the damn thing. You can't cheap out on stuff like this.
 
#16 ·
It's certainly possible for the water to flow too quickly for it to absorb enough heat, but I don't think you're going to get that with a gutted therm. My e30 and several other cars don't over heat with the thermostat out, they run cold as one would expect. Never done an e46, can't imagine it has that substantial of a water pump though.
 
#18 · (Edited)
It's certainly possible for the water to flow too quickly for it to absorb enough heat, but I don't think you're going to get that with a gutted therm. My e30 and several other cars don't over heat with the thermostat out, they run cold as one would expect. Never done an e46, can't imagine it has that substantial of a water pump though.
No, that's not how this stuff works. Increased flow rate will increase heat transfer except in very rare cases. It will keep the difference in temperature between the object being cooled and the water at a higher value. It's as simple as that. You don't have to give water time to "absorb" heat. Take this from the guy who built a model of a pressurized water reactor which is very similar to our cooling system.
 
#17 ·
yup- thermostats are there for more than just one reason- open when hot :) its got to slow the water down and also close when too cool ;)
 
#19 ·
:smh: take it from me, the guy who works on them for a living. not from models, not from theory.


you let the water go too quickly- it gets ALL of the water at the same temperature, no heat is shed off in the radiator- it overheats. im done arguing with people who dont realize experience and SEEING IT beats theory and ideas.
 
#20 ·
you let the water go too quickly- it gets ALL of the water at the same temperature, no heat is shed off in the radiator- it overheats. im done arguing with people who dont realize experience and SEEING IT beats theory and ideas.
No. The water will absorb heat no matter how fast it's flowing in a system like this. There's a reason cars with stuck open thermostats often never reach operating temperature - flow rate is too high and therefore the fluid transfers too much heat. As flow increases more and more, the system will remove as much energy from the system as the radiator is capable of dissipating.

If when working on a car there was ever a time when the temp was stable with a certain amount of fluid flow and then increased/overheated when you increased the flow, I promise you there was another variable you don't account for.

I also guarantee that BMW used this very same "theory" to design the cooling system, and used many other "theories" to make the engine work as well as it does. Outright dismissing the physics that makes design of these cars possible is silly.
 
#21 ·
:SMH: again. a stuck open thermostat STILL has restrictive qualities to slow the water down enough to make it work. yes, it is open, yes it wont go to correct temp, but there is still restriction in the system to make it work.

a GUTTED thermostat does *NOT*.

once again, you are note accounting for a variable: i have seen this a bunch of times. i have touched thousands of BMW's. care to wager who is right?
 
#22 · (Edited)
It's possible that with no restriction, the system can't build up enough water pressure to work as designed. This could potentially lower the liquid's boiling point enough for it to vaporize and no longer cool as it was designed to.

Either way, your logic in your previous post is wrong and your cause and effect wrong as well. Increased flow rate, all other conditions equal INCLUDING water pressure, fan speed, etc, will always result in higher cooling capacity, and there is absolutely no such thing as a liquid flowing "too fast to cool."
 
#25 ·
i dont know what it is that makes me smirk about the situation. and yes, i have run across "you types" before working on their cars..... i love engineers and "educated" people tell me how to fix their cars lol

street smarts > book smarts.
 
#26 ·
I'm just telling you that your cause and effect analysis is wrong. It is not happening because the water is moving "too fast". Like I said, it doesn't work that way god damn it. Also, we engineers design the stuff that you make a living off of. We know the actual principles under which it functions. Apparently you do not. You may know how to troubleshoot down to a part but don't ever think you'll one up me on something like thermodynamics or heat transfer. Those are fundamental subjects.
 
#27 ·
Going back just a bit to the 'what's this white powder' all over my engine...that is a leak.

You said that you had steam coming from your bleeder before, and when you wrote that, I thought the bleeder was closed...if so, there's a big issue for you.

If steam is getting out, air is getting in.

You also seemed to indicate that you bled for 15-20 mins. with the car on...not official bmw bleeding instructions. See Mango's sticky or search me for "alternative bleeding method" (where you rev car quickly when it's cold).

The radiator getting blocked after 2 years seems unlikely. But, as your lower hose is cool, I guess the overheating is getting picked up by some sensor other than on the lower hose. Lower hose should be cooler, of course in proper use...but also, you know, if your wp isn't working right, that would affect circulation considerably too. I believe you could have an issue where the impeller is loose on the shaft, even though it feels firm. I know that happens on PS pumps.

I've read that if you see water squirting into the top of ET (start car when cold and see if you see a stream)--then wp is okay. Otherwise, there you go.

I'd start with bleeding again the proper way...and look for something 'misting' coolant (bleeder, temp sensor, ET cap)...shouldn't mist. You're letting air into system, which could cause a bubble to block passages and/or cause wp to cavitate.

I won't argue anyone about thermodynamics. I actually studied that in college many years ago, but it seems to me that the radiator is going to remove heat at about the same rate, based on the speed you're traveling and air temp. If the coolant is moving faster, it just seems like it'd maintain an equilibrium at some temperature, other than overheating. I hope so...I've passed along the 'trick' I'd read of removing the therm from housing, and won't again if the mechanic wins the argument over the engineer.

Anyway, WDE, although I believe you, I also trust the experience mechanics have. As you say, 'you' engineers design the things mechanics make a living on. You might know the actual principles involved, but evidently, some parts you engineers are making so the mechanics make way too much money on, because they fall apart all the time! LOL
 
#28 ·
thats why i love working on cars. i fix engineer and manufacturing mistakes daily. i also enjoy being the "uneducated dirty mechanic" who doesnt know jack ****, since im not "educated" ;)...... and normally make more than the person who brought it to me lol
 
#29 · (Edited)
This isn't engineers vs mechanics. That is a stupid battle. We have completely different jobs. Stop making such an effort to be offended. Nobody said you were "uneducated" or "dirty". When we have a problem at this plant, guess who I go talk to first? I talk to the guy on the assembly line. I have no problem taking opinions/analysis from someone less "educated" than me. Just an example.

Anyway, my only problem was with your analysis of the cause of overheating as a result of thermostat gutting. The cause of the overheat could be the gutting of the thermostat, but the mechanism (the real cause) is not as you described. That would be the fact that a high flow rate can cause a higher temperature. That is false. That's all I was commenting on. That falls into my realm of knowledge. I didn't bust my ass for several years to argue fundamentals of physics on the internet.

What falls in your realm of knowledge is that sometimes gutting a thermostat can cause an overheat. For you the theory behind it does not matter. The only thing that counts is that you know gutting them can cause the car to run hot for some reason. You don't HAVE to go farther than that. That is all.
 
#30 · (Edited)
umm, have you looked at the water pump? If it had a plastic impeller and that disintegrated, that'd explain your symptoms.
And your cap might be stuck- that happened on the E36, and it blew parts apart pretty regularly
until I changed it.

On the 2002, E21, E30 and 36 (and probably E46), if you pull the thermostat, it defeats most of the cooling system, as the thermostat is a
'dual' valve that redirects water from flowing just through the block to (partially, usually) flowing through the block, then
the radiator. So if you pull the t- stat entirely, it might cool ok at idle, but at speed, it isn't flowing enough water through the
rad to really cool the engine.

Another really quick test. when stone- cold, pop the reservoir cap to make sure there's no pressure in the hoses, then replace the cap.
start the car, stab the throttle hard 2 or 3 times to 4k or so, then switch off. Then see if there's pressure in the hoses.
If there is, that's a SURE sign of a leak from the cylinders to the cooling jacket.
If not, it MIGHT only be leaking hot...

And from past experience with older cars with 'non- bypass' cooling systems , remoing the t- stat entirely made the things run
cold, until the radiator was overloaded, and then they overheated just like they did with a thermostat. The water didn't go by 'too fast' to cool...

t
 
#32 ·
And from past experience with older cars with 'non- bypass' cooling systems , remoing the t- stat entirely made the things run
cold, until the radiator was overloaded, and then they overheated just like they did with a thermostat.
t
Holy crap another person knows what I'm sayin from personal experience :excited:
 
#31 ·
Seriously sounds like just a blockage... or a waterpump is shot... does not sound like a compromised head or gasket... it would have turned up in the hydrocarbon test as the cooling system cycles though the expansion tank. Seriously just sounds like coolant is not being cycled through the system for some reason. I feel your pain :banghead:
 
#33 · (Edited)
Ahhh, thank all of you guys for helping me out. But seeing you guys arguing over the theory vs experience, feels like I'm the one caused this argument! So please, let's take it easy and do our favorite thing: solving the problem :craig:
Anyway, I'm really relieved because it sure doesn't seem to be a damaged head/HG. Numerous test & evidence, and your opinions convinced me. Now I need to find what the problem is.


So, today's diagnosis.
After replacing the radiator and flushing out the system real hard by using garden hose while let the engine running, car overheated at idling again. :facepalm:
Since I used garden hose, system was full of water. No presence of antifreeze coolant. It seemed safe to run the engine with 100% water since the pressurized system raises the boiling point, and according to OBD2 reader, coolant temp did not go over 210.

Temperature needle was guarding its post in the middle just fine for at least 7-9 minutes, and lots of air was coming out of funnel as if the water was boiling.
(*I used this funnel.)


But, at certain point, air stopped coming out. Then the needle went AWOL-overheated. Needle didn't hit the redzone, but it certainly fell toward right, just before the 3/4 marker. I'm not sure why, but it did not continue to lean toward redzone til I turn off the engine. I saw the tilted needle when I got back to my car, but didn't turn off the engine for 10 seconds because it didn't move at all. So...2 hours of flushing and bleeding wasn't really helpful, only narrowed down the source of problem a little. Sure did prove that my theory(or belief) based on 'gutted thermostat test' was false, as the car exhibited almost identical symptom.

But here's something interesting.
1) Lower hose was little warm til it overheated. After the engine overheated, I touched the lower hose and it was really hot and hard, just like upper and my thing. Radiator was cold, though. No wonder.
I thought the one of the most obvious symptom of stuck-closed thermostat was 'overheat while driving, hot-hard upper hose, cold-soft lower hose'. Maybe me being confused...
*I'm not sure I've mentioned this before, the water pump is in good condition: the impeller is composite and shaft was holding the impeller firmly. No spin or whatsoever. So, if the water pump was shot, temperature needle wouldn't even hold the ground for 3 minutes, right? Also the engine did not overheat during the test drive performed every time after I made changes.

2) After turning off the engine, thermostat housing made some weird noise.
The noise was quite similar to the noise of engaging solenoid or valve, short burst of mid-high pitch'd noise. Or water getting boiled inside.
Thermostat made this noise several times periodically and rapidly, stopped after few seconds.
And I saw this metal probe connected to a thermostat connector before, so I gotta ask this. What in the world is that? Is that some kind of heating rod which receives current and forces the thermostat to open? If it really is, then I might be looking at the whole new problem--bad ECU...


Oh GOOOOOOOOOOOOOOOOOOOOOOOOD this seems to be going nowhere.
I'll be taking out the thermostat and put it in actual boiling water, see if it opens or not.
Also I should figure out what the metal probe is, so I can make another theory.

And hey, thank you guys so much for taking time and effort to help me out. :thumbsup:
 
#35 ·
I skimmed your problem- sorry if its repetitive- If you can bypass your heater control valve that would tell you if it were the hcv- just connect the two hoses that go into the valve but make sure you know the inflow and outflow hoses for reconnection- the valve is on your drive side strut tower below your intake/maf. - the return hose that goes to your expansion tank can be left in place- I've heard you can also unplug that sensor and if you get heat it's the valve if not spend your time elsewhere- i took mine out and took it apart- turns out after time the seals fail/particles get into your system and the fluid fries the solenoid-** this wouldn't explain your overheating issue as this just allows hot fluid to the heater core- Have your tried a reverse flush on your whole system? Draining the block and all? Before that I would make sure your water pump is working properly- easy way to check is to take the expansion cap off and start your car (do this cold so you don't end up a burn victim) you should see a stream of fluid coming out the side- a failed water pump would cause both symptoms of no heat/ overheating-
 
#36 ·
the pee pee squirter in the expansion tank will tell you if the water pump is functioning.

will you put an effin thermostat in the effing engine please?

you have massive air pockets and a bad thermostat (still) it seems..... a coolant evacuation system would solve 1/2 of this.
 
#38 ·
Lol! Guess I didn't state the fact that I've already gotten a new replacement from oreilly and installed it.
So, new(might be defective, will check in few hours. DIVE, DIVE, DIVE!) one is in the engine, still exhibiting the same symptom.
I suspected a defective part, so I already bought a Behr thermostat. It will be installed as soon as I'm done with testing oreilly replacement thermostat.

Oh and mcbridges11, I'm glad you pointed that out. Stream of water does come out from the side of expansion tank when the engine's running. So I believe I can safely assume that water pump is working well.
 
#40 · (Edited)
@


I wish I had choice :banghead:
Had to attend school daily, rental was way too expensive, no way I could had gotten 50 miles of ride back and forth til parts arrive, etc.
Circumstances weren't my friend lol. Now I'm replacing everything with OE parts. Hope it solves the problem..


By the way, does anyone know what the metal rod is? I did some googling, some say it's a heating rod as I suspected, but I need second opinion..
 
#41 · (Edited)
I wish I had choice :banghead:
Had to attend school daily, rental was way too expensive, no way I could had gotten 50 miles of ride back and forth til parts arrive, etc.
Circumstances weren't my friend lol. Now I'm replacing everything with OE parts. Hope it solves the problem..


By the way, does anyone know what the metal rod is? I did some googling, some say it's a heating rod as I suspected, but I need second opinion..
metal rod? IDK there are lots of metal rods on our cars. Of which dost thou speak?
 
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