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Q: Cooling system exploded, but told it's a blown head gasket, what is going on here? on 2002 Mitsubishi Montero Sport

1. Battery died, opened hood, reservoir top was off and reservoir full of rust-colored mud-like crud. Car never overheated. (Would start to get hot if idled for long period in Las Vegas summer sun, but NEVER overheated.)
2. Had a shop flush cooling system. They said it was "pretty bad." Agreed.
3. After that car began to overheat while driving, then within a few days the rust-colored "mud" was back. Inside of engine compartment sprayed with the stuff, and marks dripped all over driveway. If coolant/water added, car ran at optimum temp.
4. Car has full power, no missing, smooth idle, no odd sounds, no visible exhaust, no water in oil, no oil in water, but sometimes emitted odd, not sweet, burning smell from engine. Sometimes sounded odd upon starting, but if I shut off car then immediately restarted, no odd sound. (Almost like exhaust-leak sound.)
5. Returned to shop to have them re-flush system, thinking they hadn't done it right the first time due to return of crud and new overheating problem.
6. Shop informed me (after performing a "test") they were "100% positive" car had blown head gasket. Would not re-flush system-"didn't want to make it worse."
7. 160k mi on engine, out of work, $2500+ to repair, so I bought reputable liquid fix ( and took to another shop to prep car for adding repair stuff. They flushed system, were supposed to remove thermostat, add 100% water, add repair stuff, and I was then supposed to drive at highway speed for 20 mi to "set" stuff. If car overheated, instructions said cool off, add water, and idle for 5 min. Took to highway speed and car ran at optimum temp for first 17 miles, but on long uphill on homestretch temp gauge climbed up, got home, cooled it off, added water, idled as instructed. Next day, car overheated at 35mph within a few miles from home. No more rust-colored mud- just grayish water. The gray color from repair stuff. Was mud gone- or stuck and lurking in system?
8. Discovered reason for spray in eng. compartment-- reservoir fill tube that rubber tube slides onto was cracked, everyone missed that one. Installed new reservoir and radiator cap because old cap was worn. Test drove car and it ran at optimum temp running hard up and down local hill near home, maybe 10 miles total, however on the last pass uphill temp started to climb fast. Coasted home. The water was boiling away inside system--loudly. Let cool overnight. Added water. Drove car again, under 30mph, only 3 miles when overheating began in earnest. Added water later on, tried again. Overheating within 2-3 miles at slow speeds.
9. Instructed to put a new thermostat in, thinking car was running without thermostat b/c the shop charged me to remove thermostat. RXAuto tech said some cars need thermostat. Tech thought shop had left air in system and the car overheated b/c of air pocket.
10. Upon new thermostat install I discovered old thermostat still there, looking all worn out. Figured that must have been part of the problem, if not THE problem causing overheating. Installed new thermostat, checked all hoses, bolts, all good. Broke a nail. Added fresh water and rest of repair stuff as instructed. Idled with cap off for a few to get air out (someone else told me to do that.)
11. Test drove car: went 4-5 miles at 30-35 mph. Temp gauge just below normal mark. Car running great! Happy as can be! Short lived though. Got on freeway for 1.5 mi, 0-65 mph, free as a bird. At 60-65 just before exit ramp the damn temp gauge climbed so rapidly there was nothing I could do but coast up the offramp to the (dammit) red light and BOOM! from under hood, steam and liquid shooting out both sides of hood. No one next to me, no car or m/c--the one good thing. Sat steaming at stupid light FOREVER... (light green, slowly headed home, temp gauge rapidly falling lulling me into a sense of false comfort) defeatedly limped home with heater and fan full blast. Repair stuff everywhere on grill front q. panels, etc. Thought the reservoir had blown its top, but NO, not my car--- the top of the damn radiator blew off! Needless to say, I need a new one, but just FYI, the inside of the radiator now exposed is all rusty.
12. Even though this happened, as I limped 1/2 mi home, the car actually ran great- even better if I ignored the crap sprayed all over the outside of it.
13. So, what do you think of this? Is this a cooling system issue, a blown headgasket, or both? (Yes, I realize that NOW it has definitely BECOME a cooling system issue, but what caused this to begin with?) What was the mud? What's up with the blown h.g? (The shop who diagnosed it had nothing to gain at all by saying it.) What caused the top of the radiator to blow off? I installed the thermostat the right way--in the exact same position as the old one. The reservoir cap, which should have blown off seeing how it offered the path of least resistance, stayed on just fine, or is that normal when a radiator blows up?
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Let me try to sooth your patience a little. Coolant systems have to be maintained perfectly to operate properly. First, I hope you are not running pure water though your car. That could be problem 1. Second is the sealant "stuff" you referred to, which isn't good for anything, exccept blowing up radiators. If it is your head gasket, there will be one of three symptoms, (1) white smoke out the exhaust (2) oil in the antifreeze reservior.(3) failed compression test , those are the only reasons to change the head gaskets, unless you're leaking oil, but you didn't say that. Even though you live in warm climate, it doesn't mean you shouldn't use antifreeze. Water has a low boiling temperature (lower than the operating temp of a car), when it boils and turns to steam, at can easily blow apart a radiator and power millions with electricity for that matter. The sealant "stuff" only makes a radiator more inefficient, it gets clogged in the cores of the radiator, no real mechanics use it. Antifreeze is also an anti boil chemical. most vehicles operate around 175degrees to 215degrees farenheit. which is alot hotter than cooling systems with only water can handle now days. Older cars could do it because of the over sized radiators and extra space in the engine compartments. Newer cars require you to use antifreeze, and yes, be aware of vapor-lock. Fill the coolant when the car is cold and running. After the thermostat opens the level will drop and you can then top it off to the warm level line. I hope this helps. Oh yeah, get a new mechanic.
Thank you for taking the time to help me with my problem. I reread my "story" and it is interesting to note the progression of the overheating issue. I don't quite understand it, and wonder if that clues you in to anything.

To clarify something- I have maintained the cooling system and am aware of how antifreeze/coolant works and that running straight water can rust/damage the system, so I always use coolant/antifreeze and have never run straight water through the system.

However, in order to properly apply the sealant the system must be flushed and cleaned, then 100% water is run through the system with the sealant mixed in for a week or so, and once the product is set the system is flushed and then a regular mixture of coolant and water is used.

Did you go through their website and watch the demo as well as read about the product I used before saying that the sealant "isn't good for anything"? I remember "Stop Leak" and you are right- it wasn't good for anything. An old friend of mine is an owner/operator with a small fleet of semi-trucks (Freightliner and Peterbilt) and he was the one who actually recommended the product to me. He used it on one of his trucks "over 100,000 miles ago" after another owner/operator told him about it, and now he is convinced.

The first shop I went to used a "block test" to determine the car has a blown hg, but what I don't understand at this point is that the car never overheated ever, then started overheating after the first cooling system flush was done. I am not saying that the shop did something to that made it start to overheat.

Also, what did you mean by "beware of vapor lock"?

Thank you again! (:
An excellent answer from Gearhead1979.
Un-maintained cooling system could cause this. Straight water or old coolant in the cooling system will results to high electrolysis (google it if you are not familiar with the term) which will eats up the metal parts of the cooling system, including head gaskets. If compressed gases - like combustion gases - enters to the cooling system due to a failed gasket, it will cause explosion. That's what happened with your radiator.
Now it will cost you the $2500 + a radiator + more work to get rid of the stop leak additive - which are pretty much worthless, actually create more problems, as you can see.

Thank you for taking the time to help me. I posted a reply to Gearhead1979 and maybe you can address what I wrote there as well as here.

What do you make of this: my car apparently has a blown hg as indicated by the results of a block test. My car never overheated ever ever ever until after the first cooling system flush. Then it began to run hot. It always always ran at optimum temperature. Right after the flush, (where they added a mix of antifreeze/coolant and water), the car could be driven at any speed for however long as long as I continued to top off the system with coolant/water. I had to do that often, and at one point when it began to get worse was if I was stopped at a red light idling. I had to continually add coolant/water because at that time, unbeknownst to me and the original shop who had flushed the system, the reservoir had a crack in the plastic tube coming out of it and when pressure built up in the system as the car warmed up, the coolant/water was spewing out of that cracked tube.

Anyways, It went from that to the radiator's top being blown off due to the temperature gauge in the red zone after a one mile drive on the freeway. Prior to getting on the freeway for the test drive I had driven the car about 5 miles and the temp gauge hovered just below the optimum center mark.

So the block test showed the car has a blown hg, and the car went from never overheating to overheating right after the system was flushed. The following trip to the shop to get it re-flushed is when the block test revealed the blown hg. The overheating problem has progressively gotten worse to the point the top of the radiator is blowing off.

Any more thoughts on all of this? Thank you very much for your opinion and help!
I CAN TYPE IN BIG PRINT TOO! But that would be silly.If it ain't broke-don't 'fix it'! Sometimes no matter what the sales rep from some of these 'flush' companies say , a simple 'drain & re-fill' -possibly more than one time though, may do more good without causing such a shock to the system and without adding or taking away from the normally used fluids. In the case of the cooling system ,removing the thermostat causes both increased flow rate/pressure in the system and also a drop in normal operating temp under many circumstances.You should not drive the vehicle with the t-stat removed.Drain & fill......Prefferably with factory coolant.Since a simple 'drain and fill' does not empty the system completely , that is why you may want to do it twice.Always put the factory specified thermostat in , unless it's defective that by itself WILL NOT cause overheating.
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