Steam coming from overflow tank - Chevy Impala SS Forum
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post #1 of 19 (permalink) Old 07-17-2019, 03:01 AM Thread Starter
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Steam coming from overflow tank

Hi guys,

I've been chasing and fixing all kinds of problems on my 180k mile 94 9c1 but i figured this is probably big enough to ask for some help.

I recently did my opti and waterpump and yesterday I noticed some steam coming from the overflow tank cap. I immediately (after finding a thick leather glove) screwed the cap down really tight and steam was still slowly coming out. I also heard a bubbling sound but there is typically some bubbling or pressurized gas leaking sound whenever I turn off the car and I thought this was normal and never noticed steam other than one time whem the tank boiled over. Should steam be coming out or should everything be sealed up? Also is there really no rad cap or is my radiator not the original style? The gauge did go up to 1/2 for a bit just before I shut the car off and it usually sits between 1/8 to 1/3.

Before I replaced the coolant temp sensor in the water pump (did this prior to opti and wp) the system overflowed (and over heated) when attempting to clean the throttle plate and engine using seafoam spray. This was the only time the engine over heated since I have owned it (5k miles or so) and it was because the fans never came on presumably due to a faulty sensor in the water pump.

My initial guess was I have a bubble but I already bled the air. I haven't bled since the initial bleed I did after the opti and wp swap, but I did it 3 times and the second time had no air from the beginning. Third time was just for fun lol.

Does this mean my head gasket is shot? When I first bought the car I noticed some water in the valve cover (white gunky residue) on the passenger side. I figured it was just from sitting for a long time and getting condensation but now I'm thinking it's the head gasket. Any way to verify this and is there any easy fix or even a band aid that will get me through another oil change or two? I will be able to do a rebuild once I move in the next 6 months or so (I don't drive much).

Also the motor often makes a pretty rough (kind of like a metal to metal contact) sound when starting. Sounds a bit like when an engine runs out of gas but only for a second. Not sure if it's related or not.

Otherwise the engine runs super strong and never overheats but has a rear main or oil filter adapter leak.

Thanks everyone!
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post #2 of 19 (permalink) Old 07-17-2019, 04:30 PM
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Can you have the cooling system and cap pressure tested? Caps can fail, overflow tanks can crack, etc.
You can take an oil sample and send it to Blackstone Labs in Fort Wayne, IN. Their report will tell you how much coolant contamination you have in the oil.
Condensation will collect in the oil fill tube, it is not necessarily an indication of a blown head gasket.
The noise on starting could be a poorly fitted starter, some require shimming to get the clearance correct, or the flexplate could be cracked.
Most common location for an oil leak is the rear of the intake manifold, second is the oil filter adapter. FelPro gaskets fix either or both.

Ken
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post #3 of 19 (permalink) Old 07-17-2019, 11:00 PM
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It is not an overflow tank. It is a reservoir and a cap that are part of the pressurized system.

Think of it as an extension of the radiator.

Your cap may be bad. If original - get a new GM part.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Have you tested your thermostat? Rent a pressure tester and test the whole system.

https://www.amazon.com/ACDelco-131-1...24982-5105528?

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Last edited by grandpas wagon; 07-17-2019 at 11:15 PM.
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post #4 of 19 (permalink) Old 07-23-2019, 07:05 PM
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Steam?

When you swapped out your water pump, assuming it is a stock pump, did you take the 'gear sleeve' off of the old pump and put it on the new pump? I had a tech change my pump and he could not figure out why the engine temp went up, and the heater would not get hot, until he looked at the old pump and said, "****'.
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post #5 of 19 (permalink) Old 07-25-2019, 09:54 AM Thread Starter
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Quote:
Originally Posted by NiteOp View Post
When you swapped out your water pump, assuming it is a stock pump, did you take the 'gear sleeve' off of the old pump and put it on the new pump? I had a tech change my pump and he could not figure out why the engine temp went up, and the heater would not get hot, until he looked at the old pump and said, "****'.
I almost did that! Fortunately I caught it 5 min after bolting the pump on and before trying anything so the gasket sealer was still tacky and I was able to get it in easily without issues. My heat does work and the car doesn't over heat. Never been past the middle of the dash gauge anyways.
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post #6 of 19 (permalink) Old 07-25-2019, 10:02 AM Thread Starter
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Quote:
Originally Posted by Ken Hennessy View Post
Can you have the cooling system and cap pressure tested? Caps can fail, overflow tanks can crack, etc.
You can take an oil sample and send it to Blackstone Labs in Fort Wayne, IN. Their report will tell you how much coolant contamination you have in the oil.
Condensation will collect in the oil fill tube, it is not necessarily an indication of a blown head gasket.
The noise on starting could be a poorly fitted starter, some require shimming to get the clearance correct, or the flexplate could be cracked.
Most common location for an oil leak is the rear of the intake manifold, second is the oil filter adapter. FelPro gaskets fix either or both.

Ken
I can probably get the system tested but I'll probably just get a new cap since it is probably that. It only vents steam whem the engine is near mid way on the gauge and only from the cap. I'll send in an oil sample at my next oil change and see whats up.

Even before I put in the new starter the engine made this noise. It sounds like lifter noise maybe but only for a second and not every time it starts but maybe 70% of the time. I cant recall if its worse with engine warm or cold but I think it's worse when the engine is warm. I didn't inspect the flex plate but wouldn't that contribute to a continuous noise?

I'm still hunting this leak. I think its my rear mains or the oil the oil filtet adapter. But im still struggling to get the back of the motor clean to fully verify its not the intake.

Thank you so much!
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post #7 of 19 (permalink) Old 07-25-2019, 10:08 AM Thread Starter
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Quote:
Originally Posted by grandpas wagon View Post
It is not an overflow tank. It is a reservoir and a cap that are part of the pressurized system.

Think of it as an extension of the radiator.

Your cap may be bad. If original - get a new GM part.

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Have you tested your thermostat? Rent a pressure tester and test the whole system.

https://www.amazon.com/ACDelco-131-1...24982-5105528?
I have not tested my tstat. How do I do this? I know its relatively new and I was told by previous owner it was a "low temp" tstat. I have the box for it somewhere. My guess is its a 160 or 180.

I'll try a new cap anyways as mine is pretty dingy and has some strange brown stain I can't get off.

Haven't seen steam in a while but still making the same strange sounds at shutdown. Not so much a boiling sound but similar to pouring water on a fire pit only much quieter.

Thanks for the info!
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post #8 of 19 (permalink) Old 07-27-2019, 09:59 PM Thread Starter
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On follow up. I topped off the coolant and tightened the old cap really good but steam still comes out from around the cap. As far as I can tell its steaming only around the cap and with it tightened really well it makes a bit of a hiss. Upon shutting off the engine the engine makes some bubbling noises as is has since I've owned it. Gonna try the new cap tomorrow.

Checked the tstat box there was actually one in it which looked new! So the one i have might be the original. The box is a 160 hypertech. I reused the tstat that was in the old wp when I did my opti and wp recently. If I knew there was tstat in that box I would have used that one although i really dont know what it is. It might not be what the box says
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post #9 of 19 (permalink) Old 07-28-2019, 08:10 AM
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Quote:
Originally Posted by Mendonmafia View Post
I have not tested my tstat. How do I do this? ......
It, and a candy thermometer in a pot of water heated on the stove.

Quote:
Originally Posted by Mendonmafia View Post
I'll try a new cap anyways as mine is pretty dingy and has some strange brown stain I can't get off.
It's a maint. item. So yah sounds WAY overdue to simply replace lol

Quote:
Originally Posted by Mendonmafia View Post
Haven't seen steam in a while but still making the same strange sounds at shutdown. Not so much a boiling sound but similar to pouring water on a fire pit only much quieter.

Thanks for the info!
Confirm for everyone you ain't just hearing air hiss back out of the intake - for like 3/4 second.

And BTW listen to Ken- up there for much the much more likely causes of a leak than the rear main.

\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear). Finally, wait for it... LT-4 knock module!
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post #10 of 19 (permalink) Old 07-28-2019, 10:02 AM Thread Starter
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Quote:
Originally Posted by 96 Black View Post
It, and a candy thermometer in a pot of water heated on the stove.

It's a maint. item. So yah sounds WAY overdue to simply replace lol

Confirm for everyone you ain't just hearing air hiss back out of the intake - for like 3/4 second.

And BTW listen to Ken- up there for much the much more likely causes of a leak than the rear main.
Wonder if my ir thermometer would work. I'll try this with the extra tstat I found yesterday.

I can confirm the hiss is not from the intake and it persists for quite a while after the engine stops running.

As for the leak it's gotten worse after doing some cleaning around the rear mains and oil filter adapter. I hope it's thr oil filter adapter though and not the mains.

This forum rules, thank youso much!
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