head gasket test

[8304]

Hi

Im sure everybody is familiar with one of the tests for a dodgy/blown head gasket is to take the rad cap off (very carefully if hot) and observe to see bubbles rising in the coolant. However, on the zx they have a kinda header tank incorporated on the left hand side of the radiator with a return pipe rising above the water level in the header tank. Should this just be water comming up through the tube or the odd bubble too - has anybody else made any observations??
Also, do people generally find any frough (is that how you spell it - i mean sludgy bubbly stuff) in the header tank??

cheers

Alastair

[AndersDK]

Hi -

Some sludge would be pretty normal as it is not possible to do repairs completely w/o a bit of oil and grease in the coolant system.
However it could be the thermostat wax cylinder has blown out the wax. This may also be the cause of the odd cold top and hot bottom of the new radiator.
It is not right to have this large temp difference top/bottom. I have to say though that the cause could be a very simple air lock that must be allowed to "burp" out.

Otherwise it is exactly the same sort of thing to look for a blown HG : regular bubbles increasing intensity with engine rpm.
But please : Never open the coolant cap with a hot engine Please

[8304]

thanks for your response AndersDK,

I have no real reason to suspect the gasket - no water in oil or oil in water or bubbles - it ws mainly for my own interest.

but if the wax stat had released is wax into the water it would stop working wouldnt it? so i dont think mine has done that because on start up the engine revsat about 1100 rpm and the drops to about 900rpm when warm.

If the h/g had gone would it be reasonable to expect a constant discharge of water and or pressure from the radiator pressure relief cap as the combustion gasses pressurise the system above what it is meant to run at??

cheers,

alastair

[AndersDK]

The coolant system will always pressurise to some 1.5bar which is the limit in the cap valve. This pressure is quite a "fizz" when you remove cap on a cooled down engine - completely normal.

It is correct that a blown HG would expell the coolant as the pressure will constanly build up higher than the 1.5bar then. The worse the HG failure the faster the coolant is expelled.

The coolant thermostat would predominantly fail in the constantly open position by design (to avoid the engine boiling out). This has the effect that the engine is slow to build up the normal working temperature.
Exactly why an alarm bell rings me when you tell me about the odd top/bottom temp diff.

Like the HG bubble test - the thermostat is also very easy to do a sure test on :
From cold (by that I mean morning cold ) engine start engine and allow to idle.
While the engine idles keep your hand on the large top hose leading to radiator from engine.
This hose should remain cold for the approx 5min engine warm up time - and then rather abruptly raise in temp to the scalding point as the thermostat opens.
This indicates a perfect condition thermostat.

If the top hose however slooowly warms up for ages - it is a sure indicator on a defective thermostat.
Sometimes stealer garages fits the thermostat wrong (reversed) id there is room for it in the housing. This means the wax cylinder never senses the hot water on the engine side ! Meaning only the safety blow-by hole is providing a (slow) info on the hot engine water.

[sooty]

The way I use to test for head gasket problems if the cooling system was suspected to be pressurising and using coollant. Was to place a container where ever possible near the overflow pipe and place the overflow pipe into the container and run as normal, then at the end of a trip check as to how much coollant was in the container over a course of a couple of days, but also checking if water level in the radiator.

If the radiator level dropped more than usual and the container filled. Then its a dead cert the head gasket is blown.

[AndersDK]

The way I use to test for head gasket problems if the cooling system was suspected to be pressurising and using coollant. Was to place a container where ever possible near the overflow pipe and place the overflow pipe into the container and run as normal, then at the end of a trip check as to how much coollant was in the container over a course of a couple of days, but also checking if water level in the radiator.

If the radiator level dropped more than usual and the container filled. Then its a dead cert the head gasket is blown.

Good test 8)
- except you must be sure the cooling system is not overfilled and then expells the normal 0.2-0.5 liter until its stabilised. There should always be room for approx 0.5L coolant in the header tank or filler neck at cold engine - to allow for coolant expansion when hot.

[8304]

Hi

Thankyou everybody for your comprehensive responses.

Anders, you have put my mind at rest slightly as i was worried that after flushing and re-filling my system i found that there was a constant dribble comming out of the over-flow pipe for a couple of days. i did indeed fill the header right to the top when cold (incorrect) as i saw the max mark on the side and assumed thats where it had to go up to. The dribble stopped a couple of days after and the level has stayed constant.
I was also a bit worried about the fizz when removing the cap - even when cold because i expected the air that had left the water to re-desolve into it as the water cooled again. This made me think it was combustion gases but if its normal to get a fizz then it must be fine.

I will have another go at bleeding the system and ill try leaving the engine running for a while whith heater off to see if the whole of the rad warms up

cheers everybody

Alastair.

[James.UK]

Another test for head gasket is to take the radiator cap off when the car engine is stone cold. This will release any presure that may have been in it, having done that, put the cap back on..

Start and run the engine for about 20 seconds, and turn it off again. Then take the rad cap back off slowly and carefully, and listen for any signs of pressure build up. If you get a 'hiss' as you remove the cap, then you have a head gasket leak!

On my ZX it's normally difficult to see the coolant without a torch, as it's about 6 inches below the top, if I fill it right up it just spits fluid back out for a couple of days, untill it has its six inches of free space back. lol..

It's a good idea to change the coolant every two years or so, as it can get very acidic if left too long. And acid eats your heater matrix!! Just make sure you get all the air out when you refill the system..