Pressure in radiator after engine is totally cool

General engine tech -- Drag Racing to Circle Track

Moderator: Team

GRTfast
New Member
New Member
Posts: 49
Joined: Wed Jul 05, 2017 8:26 am

Re: Pressure in radiator after engine is totally cool

Post by GRTfast » Wed Oct 18, 2017 2:31 pm

Schurkey wrote:
Wed Oct 18, 2017 1:51 pm
GRTfast wrote:
Wed Oct 18, 2017 7:51 am
coolant level was normal (about an inch down under the neck) where it always is.
Why is the coolant an inch down instead of full?

All the air should be blown out of the radiator into the overflow bottle when the system heats up and expands. When the system cools, only coolant should be "vacuumed" into the radiator. The radiator should be "full" with no air.
That is a good question.. it just always seems to be there. It might not be a full inch down, but it's always a little under the neck. It doesn't change though.

pdq67
Guru
Guru
Posts: 6303
Joined: Thu Mar 04, 2010 8:05 pm

Re: Pressure in radiator after engine is totally cool

Post by pdq67 » Wed Oct 18, 2017 3:22 pm

Don't the manufacturer's add a, "sealant-pill", to the cooling system when new to take care of any possible small leaks?

And did you re-torque the heads once you fired her up and let her cool down over night? I re-torque my .020" thick steel MrG shims at least twice if not three times and have never had a problem.

I use good old Permatex, "Indianhead Shellac Gasket Cement", too. Messy crap, but it works great by me. Paint the stuff on both sides of the head gaskets and let them tack up and install. I also put the stuff on the head-bolt threads and also a daub under the hex heads.

pdq67

GRTfast
New Member
New Member
Posts: 49
Joined: Wed Jul 05, 2017 8:26 am

Re: Pressure in radiator after engine is totally cool

Post by GRTfast » Wed Oct 18, 2017 3:35 pm

pdq67 wrote:
Wed Oct 18, 2017 3:22 pm
Don't the manufacturer's add a, "sealant-pill", to the cooling system when new to take care of any possible small leaks?

And did you re-torque the heads once you fired her up and let her cool down over night? I re-torque my .020" thick steel MrG shims at least twice if not three times and have never had a problem.

I use good old Permatex, "Indianhead Shellac Gasket Cement", too. Messy crap, but it works great by me. Paint the stuff on both sides of the head gaskets and let them tack up and install. I also put the stuff on the head-bolt threads and also a daub under the hex heads.

pdq67
I re-torqued (even though the gaskets are "perma-torque" style that supposedly do not need it) after a few hours of running. I did not use any gasket sealer on the head gaskets, as the instructions said not to. I think those pills are to seal leaks "leaving" the cooling system, not for ingress of combustion gasses past a head gasket.

geraldtson
New Member
New Member
Posts: 45
Joined: Tue Feb 10, 2015 9:50 pm

Re: Pressure in radiator after engine is totally cool

Post by geraldtson » Wed Oct 18, 2017 4:20 pm

Have a dirt late model same engine for many years(357sbc) it has almost always held pressure sometimes for many days even a week. Never had a problem i've seen this often. Don't worry about it,it's fine!

joe 90
Guru
Guru
Posts: 1967
Joined: Tue May 27, 2014 4:02 am
Location: The land of the long white cloud

Re: Pressure in radiator after engine is totally cool

Post by joe 90 » Wed Oct 18, 2017 4:45 pm

That's the first step in diagnosing a HG that's not sealing.
Once you start playing with boost, you'll know all about it.

Retorque the heads,that's the first step.
Never take off too much from the head deck. it weakens them........causes the problem.


I've been there many times.
Now I've got a pressure gauge hooked up to the top hose and I use my own "secret" method for sealing the "used" HGs which never leak now.
It's called RTV.

joe 90
Guru
Guru
Posts: 1967
Joined: Tue May 27, 2014 4:02 am
Location: The land of the long white cloud

Re: Pressure in radiator after engine is totally cool

Post by joe 90 » Wed Oct 18, 2017 5:47 pm

My above post (can't edit) I had to go out, was in a hurry....the first step in diagnosing a leaking HG is the residual pressure when it cools down.
It should always return to zero pressure. If it doesn't then it's due to exhaust gasses in there.

A freshly machined block surface helps too as you get rust from previous leaks, from not using antifreeze and that's porous, but you don't see it until you machine the surface.......that's a potential leak.
Same with the head, you want a freshly machined surface but never remove more than what's essential.
The head gaskets, I reuse my old ones (MLS) because they're NOT the problem.
People who sell HGs for a living want you to think otherwise.

Those coolant tester kits......they don't work........likewise, you get what you pay for....not.
They're just for noob mechanics who don't know WTF they're doing.

Retorquing the heads means putting a paint mark on each bolt, backing it off then retorquing to spec and taking note of where the paint mark starts and finishes (facing the front).

GRTfast
New Member
New Member
Posts: 49
Joined: Wed Jul 05, 2017 8:26 am

Re: Pressure in radiator after engine is totally cool

Post by GRTfast » Wed Oct 18, 2017 6:37 pm

New development. Last night when the car was cold, I took the cap off. Left it off overnight. Put it on this morning (didn’t run the car), then came home from work and there was pressure in the system. Pressure built in the system while the car sat cold in my garage all day. I think this eliminates the head gasket, lol. The only thing I can think is that the coolant additive I used is reacting with something in the water, or in my cooling system. I flushed the system and am just using straight water now. I’ll report back tomorrow.

Keith Morganstein
Guru
Guru
Posts: 5015
Joined: Sun Feb 19, 2006 10:19 am
Location: MA

Re: Pressure in radiator after engine is totally cool

Post by Keith Morganstein » Wed Oct 18, 2017 8:04 pm

What was the difference in ambient temp?
If you have a well sealed system, including the radiator cap. There is going to be an increase in pressure as the ambient temp rises.

If you aren't using coolant, there is no coolant in the oil and no coolant is pushing out of the overflow, don't worry about it.

GRTfast
New Member
New Member
Posts: 49
Joined: Wed Jul 05, 2017 8:26 am

Re: Pressure in radiator after engine is totally cool

Post by GRTfast » Wed Oct 18, 2017 8:10 pm

Keith Morganstein wrote:
Wed Oct 18, 2017 8:04 pm
What was the difference in ambient temp?
If you have a well sealed system, including the radiator cap. There is going to be an increase in pressure as the ambient temp rises.

If you aren't using coolant, there is no coolant in the oil and no coolant is pushing out of the overflow, don't worry about it.
Difference in ambient temp was maybe 5-10 degrees (I live in Florida).

I can’t imagine that being enough to make as much pressure as there was.

I’m done worrying for now. Like I said before, if something is going south, it should reveal itself soon.

Circlotron
Expert
Expert
Posts: 555
Joined: Tue Feb 05, 2013 6:56 am
Location: Melbourne, Straya

Re: Pressure in radiator after engine is totally cool

Post by Circlotron » Wed Oct 18, 2017 8:48 pm

If gas bubbles were forming in the coolant at a greater rate than the coolant contracts as it cools, that would explain why there is an empty space above the coolant level in the radiator instead of being sucked in from the overflow tank. The pressure in the radiator is being prevented from dropping below atmospheric.

joe 90
Guru
Guru
Posts: 1967
Joined: Tue May 27, 2014 4:02 am
Location: The land of the long white cloud

Re: Pressure in radiator after engine is totally cool

Post by joe 90 » Wed Oct 18, 2017 8:59 pm

GRTfast wrote:
Wed Oct 18, 2017 6:37 pm
New development. Last night when the car was cold, I took the cap off. Left it off overnight. Put it on this morning (didn’t run the car), then came home from work and there was pressure in the system. Pressure built in the system while the car sat cold in my garage all day.

Have you ever tried the same thing with a bottle of fizzy drink?


It's CO2 that dissolves in water under pressure.
Remove the pressure and it slowly comes out of solution, the speed depends on the temperature.

Circlotron
Expert
Expert
Posts: 555
Joined: Tue Feb 05, 2013 6:56 am
Location: Melbourne, Straya

Re: Pressure in radiator after engine is totally cool

Post by Circlotron » Wed Oct 18, 2017 9:23 pm

That sounds like a pretty good explanation, but why wouldn’t it happen in all circumstances? Does the coolant eventually get totally de-gassed?

GRTfast
New Member
New Member
Posts: 49
Joined: Wed Jul 05, 2017 8:26 am

Re: Pressure in radiator after engine is totally cool

Post by GRTfast » Wed Oct 18, 2017 9:41 pm

joe 90 wrote:
Wed Oct 18, 2017 8:59 pm
GRTfast wrote:
Wed Oct 18, 2017 6:37 pm
New development. Last night when the car was cold, I took the cap off. Left it off overnight. Put it on this morning (didn’t run the car), then came home from work and there was pressure in the system. Pressure built in the system while the car sat cold in my garage all day.

Have you ever tried the same thing with a bottle of fizzy drink?


It's CO2 that dissolves in water under pressure.
Remove the pressure and it slowly comes out of solution, the speed depends on the temperature.
So you’re suggesting it is a leaking head gasket, and the water has so much co2 in it that after 8-9 hours cold with no radiator cap, it still could build a bunch of pressure up once the cap was reinstalled the next day, without ever running the engine? Honestly at this point, that is just as plausible as the outgassing coolant additive reaction. I’m gonna keep driving it since I’m not losing coolant, and it’s not overheating. We’ll see what happens.

User avatar
MadBill
Guru
Guru
Posts: 12605
Joined: Tue Nov 15, 2005 10:41 am
Location: The Great White North

Re: Pressure in radiator after engine is totally cool

Post by MadBill » Wed Oct 18, 2017 9:55 pm

There's an old medical aphorism that says "When you hear hoof-beats, think horses, not zebras." No need to postulate about subtle head gasket leakage when the fizzy drink explanation fits the facts.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

pamotorman
Guru
Guru
Posts: 2288
Joined: Thu Mar 06, 2014 11:55 pm

Re: Pressure in radiator after engine is totally cool

Post by pamotorman » Wed Oct 18, 2017 10:46 pm

there is a chemical reaction going on in the coolant causing a pressure build up. happens with apple cider after a setting few weeks

Post Reply