coolant coming out boiling reservoir causing steam

1989 NISSAN 300ZX

148,368 MILES

300ZXGODDESS

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1989 nissan 300zx the coolant is coming out of the overfill reservoir and steaming everywhere. Added coolant and water to top off, and I let it run in park for about 5 minutes with no steaming. Started driving, I got about 6 miles and on the freeway and steam was coming up out under the hood. Fan clutch, hoses, belts, all fluids are good. Thinking it is either water pump or thermostat. There has been a squealing sound and it only happens when the heater is turned on and until you get up to 35 mph it stops and that did not start happening until alternator was changed 5 months ago.

I have newer timing belt, radiator and serpentine belt all done with in the past 12 months and the squealing which I thought was a loose/worn belt at first, but tension and pulleys are good. Someone told me that it could of been a possible symptom of the water pump bearings starting to go. Not sure what else to check that I maybe overlooked and appreciate any suggestions. Also how would I get the water pump off? It is behind the fan shroud and also is that where the thermostat is at? I am going to also make sure there is not any air pockets, but I doubt since I never had this steaming issue until yesterday.I do the majority of the work myself and I just bought the water pump and gasket and thermostat since if I have to pull any of it off, might as well replace these items, though when I did the timing belt last year,

I replaced the thermostat which is a lot cheaper than water pump and the water pump was fine and still could be for all I know-no leaking water anywhere under car or settle on the area where it is in car, so I hope you have a idea what I should do or check next since I really can't afford to take the car in to be fix for every problem and I normally ask online and read forums for information and troubleshooting tips since I have no car guys(father,brother or boyfriend and I'm not being sexist)in my life that work on cars even as a hobby.Thank you.

Jun 14, 2012 at 11:50 PM

CARADIODOC

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34,306 POSTS

This sounds more typical of a leaking head gasket. One clue is you may see bubbles in the reservoir before the engine has time to warm up. The test for that involves what I call the "sniffer" test. Air from the radiator is drawn through a glass cylinder with two chambers partially filled with a special dark blue liquid. If combustion gases are getting into the cooling system, the liquid will turn bright yellow.

You can often borrow that tester from an auto parts store but the fluid must not be contaminated with antifreeze or it will be ineffective. For that reason they make you buy your own bottle of the special fluid. It's usually less expensive to just have a mechanic perform the test. It only takes a few minutes.

Jun 14, 2012 at 11:58 PM

300ZXGODDESS

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if i had a leaky head gasket wouldn't i have either smoke coming out of the exhaust (white) and my spark plugs be wet and more clean? I have neither and also I have no overheating on the temperature gauge it is exactly where it is supposed to be and no coolant leaks other than coolant coming out of the overfill reservoir and when i added coolant and water it wasn't much and i haven't been dealing with low coolant levels prior to this and earlier today when i ran the car after filling up the coolant i had the radiator cap off and there was no bubbles in the coolant. i will get the tester fluid but what is the tester instrument called? my neighbor might have one if i know what it is called and other than what you suggested, is there anything else to consider as a problem if it isn't the gasket thanks again

Jun 15, 2012 at 1:00 AM

DJCL

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767 POSTS

How long can the car idle from a cold start before the coolant starts backing up. No driving and a cold start ?

Jun 15, 2012 at 1:25 AM

300ZXGODDESS

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i drove it and warmed it up prior to filling it up with coolant and water to see if the little amount that was in the reservoir would circulate back in to the radiator and then i turned off the engine got my coolant and distilled water and tester to see how much of coolant or water already in engine then filled it. in all i waited about 10 minutes after turning off car then filling up car then i started it up again and let it circulate, heard the fan kick on, felt the hoses to see if was hot for thermostat to open up. I ran it i would say for 5-7 minutes, but it was already stared up prior to letting idle so it wasn't cold start and to see if it would steam and if there was bubbles. after i replaced cap, drove to gas station which is 4 miles with stoplights and still no steaming so i drove further and it was after i got on freeway that it steamed because the coolant was hitting a hot engine where it was coming out of the opening in the overfill. it wasn't a whole lot still drove it back home and thru stoplights and such and really the only time it steamed badly is when i stopped at home, at stoplights i had to stop at 4 of them it was has bad as when i stopped at home. opened hood and looked under car for how much was coming out and it wasn't a big puddle nor everywhere on engine. i let it cool off and came out later and opened cap on radiator and there wasn't a whole lot of fluid gone i think the gylcol steam looked worse and the whole time during this the gauge never redlined or even climbed up a bit other than where it normally is when running prior to this and i have had other cars have overheating issues in the past and those gauges go up pretty quick when the engine is hot, that is why i asked if there is anything else to consider or check in case it is not the gasket

Jun 15, 2012 at 1:47 AM

300ZXGODDESS

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7 POSTS

plus just got a text from the guy who sold the car to me said gaskets were replaced when he rebuilt the engine in 10/11

Jun 15, 2012 at 1:54 AM

CARADIODOC

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34,306 POSTS

You might want to start with a simple pressure test to see if there is a leak. If there is not, try a different radiator cap. If there is a leak, look for where the coolant is running out. If anything prevents the system from building pressure, you're going to have water boiling and leaving the reservoir as steam. The radiator cap maintains 15 pounds of pressure on the system. That raises the boiling point of the water in the coolant to 257 degrees. Without that pressure, the engine can normally get hot enough for the water to boil.

Depending on where a head gasket is leaking, you don't have to have coolant going out the tail pipe. Coolant can leak outside the engine and run down the side or it can leak into an oil drain-back hole. Combustion gases can also get forced into the cooling system and if they pool under the thermostat, it may not open, leading to overheating. Thermostats only open in response to hot liquid, not hot air. The clue there is the circulation would stop and on most cars the heater would start blowing cold air.

Jun 15, 2012 at 4:22 AM