Overheating

[PPV]

I have just been out in my 3.8 and found that after about 10 miles the car started overheating with the gauge creeping up to full scale. When I stopped steam was coming out of the radiator overflow pipe. I had checked the water before going out and it was the correct level. I let it cool and topped back up but it only took about a pint or less.
When I got back home it was doing the same. I let it cool down and thought the thermostat was stuck but to my surprise when I dismantled it there was not one there! I have had the car for about 12 years or so and got it from a reputable 'refurbisher' who shall remain nameless. However that does not solve the problem. When I bought the car it did have a refurb VSE head fitted for me.
The car runs really well otherwise but it has always run at highish temp, at about 90 on the gauge. I checked the timing to see if it had moved but all seems Ok.
There does not seem any gas in the system from a leaking head gasket and it runs very smoothly, starting first time, each time.
Any thoughts, could it be the high temperature today and would a wetting agent help?
Many thanks,
Paul

[piman]

Hello Paul,

my first though is the radiator, removing the thermostat used to be a trick to 'cure' overheating but it is not a good idea as it alters the water flow.
There is little to be lost in giving the car a good dosing of a flushing agent to try and remove any silt in both the engine block and the radiator. I'm assuming the fan belt is tight and is driving the water pump?
I've not tried a wetting agent but personally I would ensure the system is in good condition.

Alec

[PPV]

Alec, thanks for the views. I have flushed the radiator and it all runs clear and appears full flow. The fan belt is fine and the pump runs quietly but I was thinking perhaps it is worn. I have run the engine with the radiator cap off and there does not seem to be any disturbance which I would have expected if I revved the engine but perhaps I am wrong. When it gets up to full temp it expands and overflows of course and then I put the radiator cap on and the temp just keeps on rising, especially if I increase the revs.
I agree with you that I should get the system working. I have tried bleeding the heater but that seems Ok and when I switch the fan on the heating points in the car run very warm indeed so don't think I have an airlock.
Perhaps it has all been just been marginal to now.
I will fit a thermostat but not sure which one. SNG say there are 3 types and the only way of knowing is to replace what is there,hence a bit of a dilemma. They say engine number does not help. My arrangement just looks like the one in the service manual but quoting the Jaguar reference numbers ( C13944 or C20766) does not seem to help.
Any views on which I should try?
Regards,
Paul

[oldtimer]

Hi Paul,
It sounds ominous to me that you found that a thermostat was not fitted. Removal of the thermostat actually aggravates the situation. Was the purpose of this to try and disguise a known problem or was the correct item not available. Either way, not professional.

Mk 2 Jaguars do not have an inherent overheating problem, I would expect to see 70 degrees C
displayed on the gauge. With a cooling system in good working order and no thermostat fitted I would expect to see a temperature of +40C to +50C displaced depending on ambient temperature As the gauge is of the bourdon tube and capillary tube type which is both accurate and durable I would not suspect the gauge. When these gauges fail it is total.

The various thermostat Part no's may well refer to the start to open temperature, that subject needs a little more investigation. When the correct thermostat is located and fitted I do not expect it to make any material difference to your problem.

The purpose of the thermostat is to maintain minimum or design engine running temperature. The thermostat remains shut until engine design temperature is reached, from there on the thermostat opens and closes to maintain the desired temperature. If the radiator cannot disperse
the heat at a sufficient rate the thermostat will open to max and the overall temperature will rise to an un acceptable level, in your case +90C.

As has already been suggested there is a strong possibility that the radiator is not satisfactory and therefore needs to be re- cored. Should you choose to go that route I would encourage you to ensure the new core has closer gills and an extra row of vertical tubes. Having removed the header tanks from flushed out radiators one can see that nothing is achieved.

Ensure the correct pressure cap is employed

I trust this will assist you in your decision making

Regards Oldtimer

[oldtimer]

PS to above , has this car had Anti Freeze at 50/50 mix for the past 12years ?

[piman]

Hello Paul,

I have little experience with thermostats specifically for the MK 2 Jaguar, however this link may be of use, as it hints at problems with current replacement thermostats. :- http://www.derek-watson.co.uk/newproducts.php
You could contact one of the club experts for further advice?

Alec

[PPV]

Hi Oldtimer & Alec, thanks for comments. Regarding antifreeze mix then I change the water/antifreeze every couple of years but use a 25% mix rather than 50/50.
It looks like I may need to take the radiator out try back flush check and if bad consider a recore/new one.
Interesting info re modified thermostat but not sure mine had that type fitted according to SNG.
Should the pressure cap be the 4 lb or 7lb one? Mine is the short type and is in good condition but I see no info on it.
I am going to check the timing again also. It is at 7degrees BTDC which should be correct for my engine unless the VSE replacement has changed the CR.
Thanks,
Paul

[Martec]

you do not say what year your car is as this may help decided what stat you should have in.

From the Magazine you will find Ken Jenkins phone number, with a few questions of what inlet manifold is fitted to your car he will probably be able to tell you what should have been fitted. If it is the sliding sleeve type stat that should be fitted then lack of this stat will result in cooling only of the front cylinders and not the rear ones, and a danger of pickup of the piston rings.

As has been said the temperature should be about 70 degrees, on a rally today our 3.8 was running a little high at 75 degrees.

If the radiator has been in use for some years a recore of your radiator may well solve most of your problems, but try the cheap options first.

Is your pressure cap on the radiator of the deep or shallow type (measure the deep of the neck in the radiator and also the pressure cap to see if it is deep enough) you can only get deep ones in 4 psi (that's what I have). If its not sealing then it will get hot.

The Watjag thermostat is a very good one, but will need a little machining of your cap (probably my next buy) or you can get a slack fitting one from other suppliers that will do the jobs (I carry one of these in the car, sliding sleeve type).

As has been said stat removal was used to hide a clogged radiator and if it is the old 'honey combs type radiator core they are not very efficient and difficult to clean (I asked my local guy to fit an uprated 4 row core in my old top and bottom tanks and have not had a problem so far).

As you have steamed up then you are definitely overheating, in my case I wasn't sure so used a remote temp sensor and a thermometer in the filler neck to check the dash temp gauge as the electric ones are notoriously inaccurate.

Best of luck
Brian

[PPV]

Thanks Brian for advice, my car is 1961 vintage, engine numberLB4894-8. I have taken my car into garage for its MOT and asked that they check the radiator for me (they are used to old cars!) and if restricted/blocked will look at replacement etc. It looks like the original rad but appears in good external condition. The cap is the short variety (approx 1 in overall dimension) and seems to be in good condition and work well.
Regarding thermostat then will contact Ken as you advise for correct one.
Regards,
Paul

[oldtimer]

Hi Paul,
The universally accepted mix for Ethylene Glycol Anti Freeze is 50/50. Not only does this provide anti - freezing properties but importantly contains anti corrosive package.

I would be most interested to hear the verdict from your local garage as to the internal state of your radiator and how they came to their conclusion. Be it good or bad.

Old timer

[peterdpps]

My 240 runs at about 70 degrees regardless of road / traffic conditions although the underbonnet always feels very warm after a run. I've had the car for over twenty years and I seem to recall it had a 4psi rad cap but when the radiator was recored about ten years ago I was told it should have a 7psi cap and I've been running that ever since.

The recoring was done to improve cooling when I had aircon fitted with an elctric fan rather than the mechanical fan.

As we are on the subject, can anyone tell me in simple terms what the advantages/ disadvantages are of the two different rad cap ratings?

I'm assuming that the 7psi will allow the coolant pressure to build up higher than the 4 psi before venting / overflowing. Is there any likelyhood of problems with the engine when using the higher rating cap?

I have always found that filling the radiator to the top always results in water blowing out of the overflow when hot and the level settles to just on the top of the core when viewed through the filler cap.

[piman]

Hello Peter,

there has been a trend towards higher and higher radiator cap pressures, generally in line with higher thermostat values.I don't believe there is a gain in fitting a higher pressure cap to 'prevent blowing off' as for that to happen means the cooling system is not working as it should. if You do run a higher pressure, then there is a greater stress on all the hoses. If you are maintaining 70 degrees or so then the pressure is probably nowhere near 7 lbs/sq inch.
As you say filling the radiator to the top does cause some coolant to blow out, due to it's expansion with temperature; it is quite a surprising amount.

Alec

[oldtimer]

Hi All,
Oh course water will overflow if the radiator is filled to the top. Water expands by 12% when heated from Zero degrees Centigrade to 100 degrees Centigrade or freezing to boiling. That's why overflow tanks were fitted to catch that water, when the water cools down it all gets sucked back in.

While on the subject, water contracts as the temperature decreases until it freezes, then a most peculiar phenomena takes place it starts to expand again. That's why water pipes in the attic split but it is not until the temperature rises and the ice melts that you know you have a burst pipe- there you are ,not everybody knows that.

Next -Take your primas stove and kettle up the mountain and the kettle will boil quicker than your mates kettle down at the bottom. Why, because atmospheric pressure is less, so the molecules jingle about earlier. The early motors had huge radiators and relied upon a syphon system to circulate the water, you know ,hot water rises and creates a flow. Next stage , smaller radiator and a pump, next stage raise the boiling point, how, stick a pressure cap on the radiator

According to the Classic S Type Manual 2 lb per sq in cap gives a flow rate of 22 galls/min and a 4lb per sq in cap gives a flow rate of 31 galls/min.

Hope that helps just a little

That's all folks 22.25 hrs and I'm getting tired

Oldtimer

[piman]

Hello Oldtimer,

what you didn't say is that the water up the mountain boils at a lower temperature, that is why it boils quicker.

I don't understand how the pressure cap affects the flow rate, that is basically dependant on the pump (engine) speed?

Alec

[oldtimer]

Hi Alec,
Either tired or too hot, I was trying to make a point about atmospheric pressure and the boiling point, I'm sure you got the point!

I don't understand why raising the cap pressure increases the flow. That's why I quoted as extracted from the Manual. I shall have to consult with my learned friend who used to design radiators and things in the motor industry. Must have skipped that physics lesson some fifty years back.

The topic is appropriate - overheating - too much for me

Oldtimer