Bubbling Coolant Header Tank

A

Andrew

CCCUK Member
Hello Everyone, I just bought a 1989 C4 (base model) with L98 Crossfire small block V8. (116k) but previous owner says rebuilt at 80k. ive had it about 2 months and really do love it already.
After a drive on saturday i noticed that the coolant header tank was bubbling for 5 mins afterwards.

I couldn't see any obvious coolant leaks , but i had noticed that the car was starting to run hotter over the past week or so.

Clues:

coolant was at right level, though the coolant does look dirty when hot. (which type shall i put in?)
No yukky gunge in oil filler cap
oil level okay
No excessive white smoke on start up i dont think (just the usual stinky petrol clouds)
The car is very low on coilovers and does do a bit of scraping over low things.

Having scoured the internet the suggested possible reasons for bubbling are:

Coolant leak
bubbles in the coolant system
old coolant-drain, flush, replace, and de-bubble
Faulty rad cap
Faulty radiator
Head gasket failure (i'm praying most strongly not)

Any suggestions?

You tube seems to suggest don't drive it/ or allow it to get too hot in this condition

I'm technically a bit inept.

I live in Farnham near Guildford. Perhaps i need to take/get the car to someone who specialises in Chevy engines/ C4 corvettes? i dont know anyone. Suggestions and help most welcomed. Thank you Andrew
 
teamzr1

teamzr1

Supporting vendor
Does the coolant level go down, and you have to keep adding more in ?
Too much anti-freeze, boils quicker the water does
Stuck thermostat
If coolant in the surge tank show no sign of oil or carbon, less likely a head gasket
Any foaming signs or coolant smell in the engine oil ?
Take 1 sparkplug out of each head and see if the plug shows an issue

Any auto parts store should sell a dye to put in the coolant also some with light a special light to
then look with that light for any signs of coolant leaking

Check the serpentine belt is too loose or damaged preventing coolant pump and/or fan not to rotate correctly
Check both radiator hoses being too old and collapses under load, feel hoses by pressing inward and see if hose is firm

What temp does the coolant gauge on the dash show ?
 
A

Andrew

CCCUK Member
Thank you JR and Pitre for your super thoughtful suggestions and hard work. Will look into this.

There seemed to be loads of coolant when hot-it almost filled up the header tank and rad was full too.

coolant looks like coffee when hot

temp over 200 (will check again tomorrow)

engine oil lovely and clear-like honey colour - no foaming

I fired the car up on the driveway 1 hour after last drive yesterday. It got hot again very soon and the fan came on before doing more bubbling. If fan comes on, does this mean that the thermostat is actually working?

maybe coolant pump broken as you say.

will check hoses and belt when light and take out plugs (to see if wet with coolant?)- thank you.
 
Pitre

Pitre

Chairman, CCCUK.
"If fan comes on, does this mean that the thermostat is actually working?"
It means that the thermostat that operates the fan is working, but not necessarily the coolant thermostat, which I would replace first.
 
teamzr1

teamzr1

Supporting vendor
May be wise in C4 being new to you is put in some good coolant cleaner than drive it around to help clean out the block and radiator
Then total drain and be a good time to replace the Tstat.
Most likely a 195 F one and go with like a 180 F degree one
It's a simple job in replacing it. Make sure the new one comes with a new gasket or get one
If in doubt, good time to replace the belt and assure no belt looseness

You will have to purge out any air pockets after new coolant is poured in
Driving around might be good enough
Not sure how you Tstat mounts but for my C5, I heat up the Tstat in pot of hot water till it begins to open
Then I place a hard pill like and pain pill and let the Tstat close, but it cannot fully close with the pill

This allows when filling with new coolant allows air to get bleed out and the pill desolves doing no harm and allowing Tstat to close

At idle watch the belt and see if the coolant fan and pulley for water pump is smoothly turning and belt not flopping around
and could check with the belt tensioner if it needs adjusting to tighten belt up

Mix like 50/50% water/anti-freeze and if your water is crappy than use distilled water
 
Last edited:
A

Andrew

CCCUK Member
Thank you Team ZR1 and Pitre. you guys are the best!

I will go shopping for:
coolant system cleaner
new coolant and distilled water 50/50
180deg thermostat temp sensor

will watch video

on saturday before hot incident car made that funny squeely noise like when a belt is slipping on an old banger.- this makes sense

Thank you for all your time and cleverness.
 
teamzr1

teamzr1

Supporting vendor
You're welcome Andrew

And when watching the belts at idle, look closely that the pulleys are running true and no wobble
 
Steven Smith

Steven Smith

CCCUK Member
C4's run very hot, fan comes on at 225°F.
The radiator is prone to get blocked, as they suck air in from under the front.
Check there isn't anything blocking the radiator.
Not difficult to fully flush radiator and engine block, that was the 1st thing I did when I got my 86.
Just remember more coolant is in the engine than the radiator, so to fully flush the knock sensor needs to be removed.
Wise to replace hoses while system drained.
Can be prone to get airlock in cooling system so when refilling coolant get front of car jacked up as high as possible, fit all hoses except the top radiator hose. Before the thermostat is fitted fill engine block with coolant, then fit thermostat and housing, fit top hose to radiator and fill with coolant until you can see it coming out radiator cap. Fit top hose, fill expansion tank and run car with radiator cap off to allow trapped air to escape, once no more bubbles in radiator fit cap and let engine get to full temperature and fan turns on.
I used pre mixed Prestone coolant as it's compatible with all types of coolant and has a 10 year lifespan.
 
A

Andrew

CCCUK Member
Thank you Keef and Steven. I feel very supported by you all! :)

i have the 160deg thermostat and Gasket on order thanks to advice from Eurovettes. when it comes. i will get hand on help with the coolant system flush and new coolant.

watch this space
 
Steven Smith

Steven Smith

CCCUK Member
Just be aware that a 160° thermostat will not make the car run any cooler it just opens earlier.
You have to get the fan to turn on earlier (at a lower temperature) to reduce the operating temperature of the system.
 
teamzr1

teamzr1

Supporting vendor
Steven Smith said:
Just be aware that a 160° thermostat will not make the car run any cooler it just opens earlier.
You have to get the fan to turn on earlier (at a lower temperature) to reduce the operating temperature of the system.
Click to expand...

A 160 F deg Tstat would too cold in winter temps effecting coolant temps for the heating and defog and take longer drive trip to get coolant hot enough for them to function better
There is natural airflow through the radiator for some cooling speeds like over 20 MPH
Using the 180 deg Tstat allows temp to be even lower to the boiling point OP is seeing than the stock 195 deg Tstat

There are products to help reduce the temperature like Be-Cool
It is a fluid simply added coolant and is sold to help vehicles taking added engine load when pulling trailers

At the top layer of the coolant is a hotter heat level, these cooling products help pull that layer of heat out and lower coolant temps 10-20 F degrees
Most auto parts stores or even like Walmart here sells these products
 
Steven Smith

Steven Smith

CCCUK Member
teamzr1 said:
A 160 F deg Tstat would too cold in winter temps effecting coolant temps for the heating and defog and take longer drive trip to get coolant hot enough for them to function better
There is natural airflow through the radiator for some cooling speeds like over 20 MPH
Using the 180 deg Tstat allows temp to be even lower to the boiling point OP is seeing than the stock 195 deg Tstat

There are products to help reduce the temperature like Be-Cool
It is a fluid simply added coolant and is sold to help vehicles taking added engine load when pulling trailers

At the top layer of the coolant is a hotter heat level, these cooling products help pull that layer of heat out and lower coolant temps 10-20 F degrees
Most auto parts stores or even like Walmart here sells these products
Click to expand...
I agree a 160° thermostat is too low but that's what the OP has ordered.
 
teamzr1

teamzr1

Supporting vendor
Steven Smith said:
I agree a 160° thermostat is too low but that's what the OP has ordered.
Click to expand...

May find than on short drives in cold weather having little heat temps

For those interested in cooling, once GM added engine controllers and went with electric cooling fans
they realized the fans require enough voltage and amperage draw that the alternator having to output often
When it is, that puts more load via the Alt/Gen pulley to crank belt that effects fuel mileage so with the controllers
can command when fan, or fans are on and off, with and without the A/C on

Interesting just how many functions of controlling coolant fans
Here are the controls set for a C5 Corvette

Fan 1 On Coolant Temp. 87 Deg. C
Fan 1 On Coolant Temp - A/C On 85 Deg. C
Fan 1 Off Coolant Temp. 82 Deg. C
Fan 1 Keyoff On Time 1 Sec
Fan 1 Run-on Coolant Temp. 139.96 Deg. C
Fan 1 On A/C Pressure 219.9 Psi
Fan 1 Off A/C Pressure 180.1 Psi
Fan 1 Off Vehicle Speed - A/C On 35 MPH
Fan 1 On Vehicle Speed - A/C On 30 MPH
Fan 1 On Minimum Engine Run Time 1 Sec.
Minimum Fan 1 On Time 50 Sec
Minimum Fan 1 Off Time 1 Sec
Fan 1 Turn On Delay Time 1 Sec
Fan 1 Turn Off Delay Time 1 Sec
Fan 1 Off Delay After Fan 2 Off 1 Sec
Fan 2 On Coolant Temp. 91 Deg. C
Fan 2 Off Coolant Temp. 87.5 Deg. C
Fan 2 On A/C Pressure 255.1 Psi
Fan 2 Off A/C Pressure 219.9 Psi
Minimum Fan 2 On Time 26 Sec
Fan 2 On Delay Time 1 Sec
Fan 2 Turn On Delay Time 0.4 Sec
Fan 2 Turn Off Delay Time 0.6 Sec
Fans Off Vehicle Speed - A/C On 90 MPH
Fan Type (0=2 Fans, 1=Aux Fan, 2= None) 0

The controller can also command at what rotation rate/speed the fans can be commanded
depending on coolant temp is

fans.jpg
 
A

Andrew

CCCUK Member
Thank you guys. I should have put my best listening ears on- I will return the 160deg version and order a 180deg version.
 
teamzr1

teamzr1

Supporting vendor
Just an FYI for those like doing the none normal like I do :)

Depending on the Tstat and its housing design
I make up and install shims to stock Tstat setups and can dictate when it opens by the thickness of the shims

Converting you stock Thermostat for lower temps

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