Water pressure

[Geoff C]

Having an ongoing problem with my SLR.

 

Pressure is buliding up and I am losing coolant though the cap on the expansion bottle.

The problem does seem rather intermittent and has only happened on two recent airfield days, after the car has been thrashed for short bursts. I have done plenty of normal driving in between with no sign of a leak (300 reasonably fast road miles last saturday)

 

One other thing, the water temp now seems to be reading higher than it used to (above 80 constantly now, instead of 60 before)

 

Any sugestions much appreciated, baring in mind I am not a very technically minded sevener...

 

Cheers Geoff

[murph7355]

Sounds to me like there might be an airlock in the system, thought it's odd that you don't see any symptoms on the road (inc. temp now might be the first sign). Also, does the water temp. seem to vary more than it used to?

 

There are other threads that demonstrate the proper way to get rid of them. The following seemed to work for me though!

 

1) Check that the coolant at least looks to be at the correct level in the expansion tank.

 

2) Get the car up to temp (over 88degC so that the thermostat opens I believe)

 

3) Make sure the heater valve is open if you have one

 

4) Jack the front of the car up as high as you can get it.

 

5) Loosen off the bleed screw on top of the radiator to let any air out.

 

Now when I was doing this bugger all happened until I took the cap off the expansion tank. When I did this, and opened the bleed screw fully nothing happened for a second then coolant started to bubble out. I then:

 

6) Put the bleed screw back in and tightened it up (making sure to include the fibre washer).

 

7) Topped up the coolant level to just over the line.

 

8) Put the cap back on.

 

9) Went for a blast to see how hot I could get the car.

 

It seems to have cured the problem on mine. It's possible you may have to repeat the above process a few times to get it right though.

 

One tip would be to use a socket to get the bleed screw on and off (mine's 17mm but I have the ali race rad', not sure if it's the same size as the standard one). That way you can "hold" the screw in the socket whilst performing the above, using a long extension to your ratchet to keep your hands away from the hot screw/coolant.

 

I'd also make sure you top it up with decent coolant (the Comma stuff is about 9 quid from Caterham for 4l).

 

Now for the doodgy disclaimer - I too am a mechanical nonce so I could be sending you off in completely the wrong direction! But it's easy to try this out.

 

One thing is for certain - temp. is critical on K's and if it goes too high (sustained > 100degC I think, but 80degC normal running doesn't sound too high) you can get all sorts of expensive problems.

[R2D2]

If you are worried about the head gasket Snap On sell a neat diagnostic system for about £40. Itis a chemical indicator that checks the water system for dissolved hydrocarbons. I bought one last year because I was experiencing constant water loss, again through the expansion system and I was convinced that the water system was pressurising. I had tried bleeding the system to remove airlocks and I was quite fed up with the worry. It is quite a useful addition to a toolbox and very easy to use.

[Swiss_Tony]

Geoff

Have you tried replacing the rad cap?

I have seen a few dodgy caps which give similar symptoms.

If the cap is faulty it could also cause an airlock in the system.

 

James

 

[murph7355]

Chris - do you have details of where to get this thing from?

 

Also, what does it do? Does it turn the coolant a different colour if there's foreign matter in it?

[Geoff C]

Andy, Chris and James

 

Thanks for your replies. In the process of removing airlocks as you suggested Andy and I am heading to Millwood in the week so I will get a new rad cap then. The car has just come back from there for a recent service so I am hoping head gasket is not the problem. However the AA man who towed me back from Wroughton the first time seemed to think it was that. (Although he did have a problem checking my oil level and couldn't understand the lack of a dipstick).hmmmm

 

 

[murph7355]

Geoff - it could also be head gasket trouble. Didn't want to worry you until you'd had a go at bleeding the system first.

 

However, if the temperature is reading only 80degC or so and your not losing too much coolant I'm not sure that it's going to be anything drastic (what colour is the fluid that goes into the expansion tank?).

 

If you've checked everything and the pointers are towards head gasket, you'll need to get it sorted sharpish. I've heard heads can warp which can then be costly to rectify (note also that stronger head gaskets are available which might be worth using should you need to change it - Mike Satur and, I think, Raceline question.gif do them). Oilyhands will know smile.gif.

 

 

[Geoff C]

Andy

 

Have just tried removing airlocks as suggested and the expansion tank overflowed before temp even reached 85. I am now hoping it is just the expansion bottle cap which I will try and pick up tomorrow.

 

The water in the expansion bottle is blue although there is a slight brown skin on it, however this has been there since I bought the car last July and I am hoping Millwood would have picked it up in the service if it had been head gasket.

 

Will keep you posted... thanks again.

[R2D2]

If you 'phone SNAP-ON they will give you a 'phone number of the Local Agent.

 

http://www.snap.co.uk/

 

Most SNAP-ON parts are supplied by a guy's who sell to the trade and operate a van delivery service.

 

The test kit is sold as a "Block Tester"

 

It comprises of a glass tube with a sintered bronze plug in the bottom and a rubber bulb to pull ait through an indicator liquid. The instructions are quite simple. The indicator ifluid is supplied with the kit.

 

basically you drive the car for a few miles top warm it up. Carefully remove the rad cap without scalding yourself press the tube into tthe cap. the ttube has a conical rubber seal. Any hydrocarbons present change the colour of the fluid from blue to yellow.

 

It had compression tested my engine a couple of times and obtained quite good figures but kepy getting a water loss, It seems that the porosity I had in the head was only evident when the engine was at running temperature and that neither the cranking pressure that the starter generated or the gas pressure at zero load caused a leak.

 

Obviously the gas pressure the engine generates at full load (peak BMEP) is much higher than at zero load and is not much affected by rpm.

 

It was disappointing to see the colour change but at least it helped me pin point the fault and solve the problem.

 

 

[Mr Locust]

Have you checked that the electric fan is cutting in. Short bursts followed by standing still are more likely to cause overheating if the fan doesnt cut in. Once you lose some coolant, the engine will tend to overheat more easily.

 

Likewise I echo the sentiment regarding the faulty caps loosing coolant. Make sure you get the right length if a conventional cap is fitted.

[Mr Locust]

Have you checked that the electric fan is cutting in. Short bursts followed by standing still are more likely to cause overheating if the fan doesnt cut in. Once you lose some coolant, the engine will tend to overheat more easily.

 

Likewise I echo the sentiment regarding the faulty caps loosing coolant. Make sure you get the right length if a conventional (old fashioned!) cap is fitted.

[Geoff C]

Looks like it was the cap, new one fitted 2 days ago and no re-occurance (yet)

 

just gotta book another airfield day to make sure...

 

Thanks for all the advice.