Re: A dumb question about coolant

Coolant level is checked cold - coolant expands a LOT as it warms and a hot engine will have a full or nearly full surge tank. As the engine cools the coolant level drops back to about half full or so.

Expanding coolant, acting against the captive airspace in the surge tank, is what pressurizes the cooling system in order to raise the boil point, suppress coolant bubbling (cavitation), and increase heat transfer.

Use the FULL COLD legend and flat arrow molded into the surge tank top. FULL COLD is about at the tank midseam.

 

Re: A dumb question about coolant

Coolant level is checked cold - coolant expands a LOT as it warms and a hot engine will have a full or nearly full surge tank. As the engine cools the coolant level drops back to about half full or so.

See, this is what I thought, and that's what's strange. When my car cools off it doesn't drop to half full, it drops a lot below that, but after I remove the cap, the pressure is released and coolant comes pouring back out of the system into the reservoir tank. From what you're saying it sounds like my coolant should be at the full cold mark even when the cap is on - and perhaps also that removing the cap shouldn't alter the coolant level at all?

 

Re: A dumb question about coolant

In a perfect world there will be NO pressure in the surge tank with the system (overnight) cold.

It's not a reservoir tank - it's a surge tank, an integral part of the pressurized cooling system. Coolant level in the surge tank varies as system temperature changes. That tank runs at system (cap) pressure when the engine is fully warmed up. There's a small constant flow through the tank due to the purge line that runs from the water crossover hollow bolt/nipple over to the top side of the surge tank. The coolant overflow is attached to the side of the filler neck.

With the system filled to the correct level, barring other faults, when cold (ambient temp cold) the coolant level should stay the same whether you check it before the first start of today or tomorrow. Depending on climate, it may take over 12 hours for the system to fully cool.

 

Re: A dumb question about coolant

I think what the OP is saying is that there’s pressure when he opens the cap system cold. This is strange, to me......

 

I think what the OP is saying is that there’s pressure when he opens the cap system cold. This is strange, to me......

Agreed. I cold system should have no pressure, especially after cooling all night.

 

Re: A dumb question about coolant

Hve the radiator cap checked. Look at the upper radiator hose to see if it is collapsed when cold, before you open the cap.

 

Re: A dumb question about coolant

I managed to find two other threads where people seem to have a similar issue although with different vehicles:

https://www.saabcentral.com/forums/archive/index.php/t-88824.html
https://www.bimmerforums.com/forum/...com/forum/showthread.php?2310806-Coolant-level-low-when-cold-pressure-in-system

I'll do some more searching since now judging by your replies it's clear that having pressure in the system when cold isn't supposed to happen, so that gives me something to work with.

Hve the radiator cap checked. Look at the upper radiator hose to see if it is collapsed when cold, before you open the cap.

Thanks, I'll do this.

 

Re: A dumb question about coolant

I'm putting my money on the cap as well.

 

Re: A dumb question about coolant

I looked up this issue on Google. Reading a thread where someone asked this question could be a head gasket issue where combustion gas is getting into the cooling system. There is a tester for this where a liquid changes color. (Not sure how this is done to be honest). Also can start the cool engine with the cap off and coolant will come out.

 

Re: A dumb question about coolant

I looked up this issue on Google. Reading a thread where someone asked this question could be a head gasket issue where combustion gas is getting into the cooling system. There is a tester for this where a liquid changes color. (Not sure how this is done to be honest). Also can start the cool engine with the cap off and coolant will come out.

=============================
a cold engine has absolutely no pressure in the cooling system -
as the engine heats up - the coolant expands in size -
THIS is how pressure builds up -

when the engine is shut off the coolant cools - and contracts - back to the original size - thus no more pressure -

the ONLY way you will have pressure in a COLD cooling system is if "artificial" pressure was added to the sealed system -
this artificial pressure typically comes from failed head gaskets -

time for a BLOCK TEST -
the special BLUE fluid reacts to hydrocarbons -
turning different colors - depending on the concentration -
lighter blue - clear - green - yellow -
but ANY color change is a POSITIVE result -

 

Re: A dumb question about coolant

Adding to this thread. Seeing the same thing on my 2004 Deville. When cold the surge tank is low and it still has pressure when releasing the surge cap. I hear a rush of coolant as the pressure bleeds off and the surge tank fills up. I'm over 110K. I have done block tests and they have been negative but as suggested I did the tests after the temp gauge went past the noon mark. Blue fluid turned green.

I have also had rough idle when cold for a minute or so. My thought was exhaust pressure in the cooling system was pushing coolant into one or more of the cylinders after shutdown. After starting I was getting rough idle maybe until the coolant was flushed out. After driving it I was letting the pressure off the cooling system by slowly releasing the cap. On the next startup no or very little rough idle. Last year I changed all the original plugs with the same AC Delco. A few months ago I was getting a misfire on cylinder 2. I swapped in another coil. Misfire stayed. New plug and the misfire was gone and the code. I'm not sure if related or not. If number 2 cylinder is where coolant might being getting into the cylinder and over time fouling out the plug. Might not and just a plug going bad.

You didn't mention overheating. Check you cap and make sure the purge line is flowing. As suggested I would also do a block test after a good run. You could be early stages of HG issue.

 

Re: A dumb question about coolant

Before:

After:

https://i.imgur.com/x49a5lr.gifv

Didn't even have to use the squeezy ball thing

Oh and yeah no problems with overheating so far, thankfully.

 

Re: A dumb question about coolant

Blue fluid changing color means there are combustion gasses in the coolant, usually caused by failed head gaskets or pulled head bolts. ask me how i know lol

 

Re: A dumb question about coolant

no question about those results -

Oh and yeah no problems with overheating so far,
don't hold your breath - the end is near -
two most common things that will cause the overheating -

once the volume of exhaust gasses entering the cooling system overwhelm the PURGE LINE -
air gets trapped in the heater core and all the way down to the waterpump -
the waterpump can't move air - and air can't cool the engine = overheating

low coolant level - nothing left for the waterpump to pump -

 

Re: A dumb question about coolant

pressure in my reservoir was the first sign i had that my head gaskets were failing, take the cap off in the morning with a cold engine and had a blast of pressure escape

 

Re: A dumb question about coolant

pressure in my reservoir was the first sign i had that my head gaskets were failing, take the cap off in the morning with a cold engine and had a blast of pressure escape

===================
that is an excellent response - informative and helpful - :thumbsup:

 

Re: A dumb question about coolant

Well, it's had a good run I suppose. I have had it since 2013 after all, and it's coming up on its 20th birthday.

Would've been nice if I could've figured all this out before I had the tranny rebuilt a few weeks ago though :suspense: I was making myself feel better about the price of that repair by telling myself "well, once this is taken care of then there shouldn't be any more big repairs to worry about for a while at least".

WRONG!

 

Re: A dumb question about coolant

If the car is in otherwise good condition with up-to-date maintenance then it's worth taking to Midwest Cadillac in Palatine, IL for a head bolt thread insert or stud job. The transmission is good - another $2500 - $3,000 for a head job and what would you spend the $5500 total on to replace it?

https://www.google.com/search?q=mid...adillac+repair+palatine+il&aqs=chrome..69i57.15419j0j8&sourceid=chrome&ie=UTF-8

 

Re: A dumb question about coolant

:yeah:

Between that and the trans rebuild you'll be able to keep it for many years to come

 

If you own the car outright, peace of mind formula is: divide cost of repairs by monthly payment for a new to you vehicle = break even. $5000 repair / $800 payment = 6.25 months from which point forward you're ahead of the game. If you like the car, it's probably worth it unless you plan to trade soon. If you don't like the car, why fix it?

 

Re: A dumb question about coolant

Hey guys, just an update. Still don't completely know what I'm going to do. It's hard for me to bring myself to spend so much fixing this car again, but it does seem to be true that once you do that HG repair the engine is pretty much bulletproof.

If I did want to get it fixed, would I really have to drive all the way to that place in Chicago?

Also, my update on the car is: I've been checking the coolant every day before I drive anywhere, both to actually check the coolant level and to also relieve the pressure that's always there being stored in the cooling system, which I figure is maybe a good thing to do. Strangely, it seems like I've been losing basically no coolant, which would be promising if it weren't for the failed block test. It's been doing the "pressure in the cooling system" thing since September of last year (at least), so clearly whatever is happening is happening very slowly.



Oh trust me if I were to get a new car, the payment wouldn't be anywhere close to $800 per month

 

Re: A dumb question about coolant

I just faced the same issues you are, bad head gasket, or stripped bolt holes. Call it what you will, the end result is the same. Nobody locally was willing to do an insert or stud job on my motor. The one guy that did say he would do it quoted himself out of the ball park and the job. I ended up buying a rebuilt motor for $3300 and a local shop swapped it in for me for another 2000.
The motor has been in the car for a month now and so far no issues, although I did just discover a leak in the radiator, that's another project for the weekend.

 

Re: A dumb question about coolant

I sent Joe an Email inquiring about price and he indicated he could R & R the engine from a vehicle, install inserts in the block, and reseal the "oil pan the lower case half and replace the rear main as well as replace all the fluids" for $2K. That almost changes my opinion about the 97-99 Devilles because I really like their styling. I wonder what else he might encounter on a typical engine rebuild (wear items, etc.) that would drive the price higher?

 

Re: A dumb question about coolant

I sent Joe an Email inquiring about price and he indicated he could R & R the engine from a vehicle, install inserts in the block, and reseal the "oil pan the lower case half and replace the rear main as well as replace all the fluids" for $2K. That almost changes my opinion about the 97-99 Devilles because I really like their styling. I wonder what else he might encounter on a typical engine rebuild (wear items, etc.) that would drive the price higher?

=========================
when Joe did mine -
I had him replace the trans solenoids - just because -

 

Re: A dumb question about coolant

All that work for $2k?...what a deal!

 

Re: A dumb question about coolant

While anything is possible, generally speaking, Joe has all the weak points covered.

 

Re: A dumb question about coolant

If he finds any valvetrain wear - cam lobes, hydraulic flat tappet cam followers, chain tensioner/guide wear - he'll inform you. That stuff is NOT cheap and is a common wear factor in the pre-2000 engines.

 

Re: A dumb question about coolant

Is there some way that I could rule out that I have a cracked block or some other issue instead of just a HG problem?

 

Re: A dumb question about coolant

If you had either a cracked block or head or a failing radiator the engine would be losing coolant rapidly as well as have radical mechanical/performance/overheat problems.

 

Re: A dumb question about coolant

If you had either a cracked block or head or a failing radiator the engine would be losing coolant rapidly as well as have radical mechanical/performance/overheat problems.

Hmm... alright. Well that's definitely not my issue. I'm hardly losing coolant at all, which is actually interesting. I've got combustion gasses in my coolant but I'm not actually losing coolant (or hardly losing it, it's hard to track it precisely because of said gasses). The gasket has failed enough to let gasses in but not let coolant out? :hmm:

On second thought I did have to add coolant a few weeks ago and quite a bit of it too, so I guess it is losing it, it's just very slow. I check the coolant level every day now and it's almost like it's not losing any at all.

 

Re: A dumb question about coolant

It appears the cylinder block exhaust gas test was positive - some hydrocarbons in the airspace over the coolant. IF the leak is small enough that exhaust gas only enters the cooling passages during engine operation then it's still a damned small leak - it occurs only under tremendous exhaust gas pressure. As time progresses and the head bolts loosen further the leak(s) will become more prominent and then coolant may seep into one or more cylinders during engine off periods - accelerating coolant loss. Eventually the leaks become so bad that the cooling system overpressurizes during driving times and actually blows coolant out of the surge tank overflow line. Rapid overheating follows radical coolant loss; some coolant loss may cause overheating due to the water pump sucking air - cavitation.

What happens is that the crushed stainless steel fire ring begins leaking exhaust gasses - that eats away the softer gasket material, leading to gasses in the cooling system. The Northstar is an open deck block so there's very little gasket material between the cylinder liner edge and some cooling passages.

The first picture is a set of head studs by www.northstarperformance.com. The second shows just how little gasket there is between the cylinder liners and cooling passages ............

https://www.google.com/search?rlz=1...sa=X&ved=2ahUKEwjy5M30vrvhAhUPyFkKHV6lBTkQ7Al6BAgIEA0&biw=1094&bih=486&dpr=1.25

 

Re: A dumb question about coolant

Just another update from today because it was interesting. When I checked my coolant level this morning it actually seems higher than it was yesterday - about half an inch or so above the full line. My first thought was that maybe oil was getting in and causing it to rise, but it didn't look cloudy or milky or anything to indicate oil was getting in, although it can be hard to tell since my overflow tank is so old and discolored, so I have to go by what I can see from peering into the hole. It's also possible that I just have too much coolant in the system, thanks to how the exhaust gasses seem to mess with the coolant level. Some days when I check it it lets off more pressure which causes the coolant level to rise higher, other days it releases less and the level rises less. A few days ago when I checked it, almost no pressure was released, and the level was actually a bit below the full line, but I left it alone, and now today it was above the full line!

It's very strange, I wish I had a better understanding of exactly what's happening. The exhaust gasses are causing pressure to be stored in the overflow tank, so when I take off the cap, the pressure is released which allows coolant to flow back out of the radiator into the overflow tank?

 

Re: A dumb question about coolant

Northstars rarely ever (if at all) mix oil with the coolant when a HG fails, so I wouldn't worry about that.

Theoretically, the radiator should be full and any air or exhaust gasses should get purged to the surge tank and releasing pressure should not affect the coolant level, unless your coolant level is so low that the surge tank is dry.

 

Re: A dumb question about coolant

Northstars rarely ever (if at all) mix oil with the coolant when a HG fails, so I wouldn't worry about that.

Theoretically, the radiator should be full and any air or exhaust gasses should get purged to the surge tank and releasing pressure should not affect the coolant level, unless your coolant level is so low that the surge tank is dry.

Well that's good to know. By the way, sorry if I'm mixing up terms here. Surge tank, overflow reservoir, expansion tank, I'm quickly learning all these things aren't just interchangeable terms :halo:

Just for clarity's sake, what's been happening most days when I check the coolant is that I can see from the outside it's right around full, maybe just a bit below, and when I take off the cap, a bit of pressure is released and along with it some coolant flows into the tank and takes it up to full. So it's far from dry, which I suppose makes what's happening even stranger.