I have a Jaguar XJ8 4.0 on a 1997 plate. It had a slight leak from the return hose so I replaced it. Since then it seems to be loosing water. I thought there may be air in the coolant system. So I left the cap off ran the engine and it overflowed slightly with lots of bubbles coming out. I put the cap back on and it seems to be needing topping up every few days. I cannot see any obvious leaks anywhere. I put k seal in it also but still the same. When driving the low coolant light sometimes comes on but then it goes off and comes back on sonetimes. Any ideas on why it's loosing water would be appreciated ?.

 

Hi Mat32essex
Every time I have seen bubbles in a radiator cap or in this case the jag top tank it means air is getting into the water system somewhere.
I hate to say but could certainly be from the cylinders caused by a blown head gasket.
you could pressure leak test each cylinder to make sure 1 or 2 are not leaking into the water venturi that cool the block
because if you had a leaking hose.
1. you would see water under the car or on the engine somewhere
2. unless it's going into the cylinder say overnight when the engine is cool.
but I really think along the lines of blown head gasket.
3. Has it overheated recently?

 

I wouldn't jump to looking at the head gasket based on air bubbles. The coolant system at temperature is under pressure and fluids leak. Once it starts to cool is creates a vacuum thus the air bubbles.
The absolute best way to find the leak is a static pressure test of the cooling system on a cold engine. Any good radiator service company can perform the test or you can by the tools to do it yourself.
The most likely culprits are the heater feed and return hoses that are under the intake manifold. Then there is the norma connector under tha throttle body. You would never see the leaks since the hot engine will boil off the water.

 

Good point aver1
it could boil the water off I got, however, I got my hand in under the norm clip and had moisture, also saw a pool of water on top of the gearbox (octopus hose split only leaked when hot /pressure)
I agree to pressure test the system is the best answer as you said a radiator company doesn't usually chare for that.

Mat said: So I left the cap off ran the engine and it overflowed slightly with lots of bubbles coming out.
overflow is probably due to water expansion, but the air getting into the system.?
also: It had a slight leak from the return hose so I replaced it.

when the engine is running the only place it should overflow when the fluid expands is down to the reservoir tank and suck's back in when the pressure drops (engine cooling down)
so as mat 32 said he ran the engine with the filler cap off.?
so where is the air coming from.?
if it was a hose would that not be a positive and leaking out not sucking air in.

is Mat you close all caps and run the engine you can not see a leak

 

If the cap is off, the coolant will boil anyway as it is not pressurised so this does not really tell you anything. K-Seal or similar will not seal any cylinder head gasket leak and, in fact, it is better not to use them as they may cause clogging of the cooling system. The easiest way to determine whether there is cylinder head gasket leak or not is by doing a Combustion Gas Leak Test. These kits are fairly cheap, around USD 60-70.

 

The car has never over heated since i have had the car. The temperature always stays just below half way on the temperature gauge.

 

Well Matt
That can rule out somethings for me
I think to follow what MS & aver1 said with the pressure test.
I'll be watching for a good outcome for you
Dutchy
my car did exactly what RJ237 said below
I pulled over straight away let cool and gradualy added water with the engine running
I wonder what the normal running temp is

 

The gauge will read mid scale until about 230F and then shoot up to red zone. Many have found it's too late when that happens because you can't keep driving to the next exit. The only way to monitor temp. is through the OBD plug.

 

I have been driving the car for nearly a week now and have not checked the coolant level. The temperature guage is still below the middle mark. Also the low coolant light is not coming on like it did before. It used to come on and then go off sometimes intermittently. It's using a lot of petrol and you can smell a petrol Smell from the exhaust though. It's not even doing 200 miles to a tank of fuel at the moment. When it starts up and is not warm it hesitates when trying to accelerate like there is a lack of fuel but once it has warmed up it is fine. Does anyone know if the water coolant low sensor is accurate ?. Also I don't want to check the coolant level unnecessarily because I always seem to over fill it which causes more issues.

 

I overfilled my car sometimes I figure the excess goes down to the reservoir tank located near the front L/H/S lights
As for the smell are all the intake air ducts sitting properly and sealing ok. so as the MAF sensor can get the mix right. have you put a reader in it yet?
that rotten coolant level kept popping out so insert the sensor and firmly click it up until it snaps into position otherwise it will drop down and give a false reading they are a bugga.
keep going mat

 

check the hoses under the throttle body.