Am I overheating?

[mtnjag]

Yes I agree but won't it will always overflow significantly more if the cap is left off or loose even if at proper level?

[PeterCrespin]

Expansion (overfilling) puking is just dependent on temperature increase times coefficient of expansion and will happen at whatever temp the water runs out of room, because water is not compressible.

Boiling point is dependent of pressure as well as temp, so will occur earlier with the cap off. But by the time a properly circulating system boils at, say, a few degrees over 100C for coolant mix, most of the expansion overflow will already have happened at lower temps.

The big problem occurs when there is true boiling due to low pressure and/or stagnant flow. Because steam occupies massively more volume than liquid water, if you get a big bubble of steam in the head it will quickly blow out any coolant between there and any opening to atmosphere - which is normally the cap.

[Philk]

Just to add a couple of thoughts.....

1) Check that the Radiator Cap is the correct model for the car/year since you may have one that is releasing at a lower pressure than it should be. For example, on my car (S1 3.8), Jaguar dealt with some of the overheating issues by upgrading the cap from 7lb Sq In to 9lb Sq In cap (with upgraded hoses introduced at the same time). NB this will not address the fact that the car is not cooling down but may address an early release of water from the radiator header tank.

2) If the Otter switch is working correctly (which it sounds that it is), the only reason it is not switching off is that the combination of the fan air movement, radiator heat transfer and water circulation in the engine is not cooling things down enough. On my car (which uses a Fosseway radiator and fan), you can begin to see the temperature starting to come down on the gauge within 30 seconds of operation. You say that you have already checked that the fan is working and is pulling air through the radiator correctly. The key question is whether it is pulling sufficient air from the right place. As such, check that the Fan Cowl is fitted correctly. This ensures that the air drawn through by the fan is sucked from across the entire surface area of the radiator. Any problems with that can mean the fan is pulling air from the sides of the cowl and not through the radiator from the front.

3) Assuming you are getting a large volume of air passing through the radiator with the fan, you could (carefully) attempt to measure the temperature difference between the bottom of the radiator and the top. A big difference means you are not getting the circulation you should be. This could therefore point to the thermostat not fully opening (as already described), the pump not working correctly, air-locks or blockages in the water jackets around the engine. Has your engine been flushed previously?

[PeterCrespin]

Also check the depth of the tank neck compared to cap height. Too short a cap in a deep neck will cause problems. There are threads here about mismatched caps & tank necks. The cap should need a good press down just to start the tabs in the neck cutouts.

[paulsco]

Hi All,

I have noted all your comments and am working through them.

As the engine had been running normally until lately I decided to start with the things I had changed. I had the old thermostat (which I tested) and a spare gasket and it only takes a short time to change, I thought I would start there.




I need to re-read the thread on thermostats, because when measuring the thermostat sleeve (on the correct thermostat), I found that the sleeve sits further down the bore than the bottom edge of the slot in the manifold, so in theory blocking it off even when cold.

From the top of the thermostat to the bottom of the sleeve is 15.80mm; from the face of the manifold to the bottom of the slot it is 14.52mm.
I say blocking off in theory, because the sleeve is 46.41mm in diameter and the bore is 48.81, so there is a gap between the two of 2.40mm.
It would seam that the sleeve needs shortening by about 1.50mm, but as there is a gap anyway it is debatable.



Anyway, I changed the thermostat, but this had zero effect

Going back to some of your points:

The engine only has about 20 hours on it and I have completely rebuilt it. The core plugs have been removed and the block flushed out.
The radiator is re cored and uprated.
The cap is 7lbs, but measuring between the two rubber seals at the bottom and top of the cap it measures 19.59mm and the neck of the header tank is 20.33mm, so there is clearly a problem here, but not I think the cause of this problem.



I have run the engine again after replacing the thermostat and now the fan doesn’t kick in till over 90c (it was around 85c before??) on the gauge and it stays on and hovers around the 90c temperature.
It didn’t actually boil over though, but going back to the point above, is it getting as hot as indicated??



I need to get myself an accurate temperature tester, but have so far been unable to do this.
I may have a false reading on the gauge, but this still doesn’t explain why the fan is not going off and the temperature is not falling.

The radiator top hose is hotter than the bottom hose.

The only other jobs I have done on the motor are to tune the carbs (may be too weak) and the ignition timing . I do also have some suspicion that the vacuum advance may not be working properly, so I will check that too.

Thank you all for input, it is much appreciated.
Paul

[mtnjag]

Probably mentioned up further but you’re advanced enough aren't you? Ignition that’s not advanced enough can cause hot running. More likely on the road than in garage i think but worth noting.

[paulsco]

Thanks Layne,

I set it about 8 degrees as I have 8:1 pistons, but Will try 10 degrees to see if it is any better. I have a suspicion that the vacuum advance may not be doing its work, so I will check that as well.

Just to elaborate on my comments above re the radiator cap: I already have the long reach cap installed and when it is tightened up and the seal compressed, it does seal.

Paul

[mtnjag]

You’re likey okay at 8, should be anyway if everything is right.

Not looking at prior posts so may be repetitive, but make sure your timing references are all where they should be.

[mystery type]

As you’ve had the thermostat out a few times Could there be an air lock? Might be worth raising the front of the car and let it run/circulate for a while with the cap off.

[paulsco]

I have checked the timing and that is correct.

I still haven’t got hold of an inferred temperature tester to check my temperatures, but I decided to experiment by removing the condenser (not connected yet) to see if the flow of air through the radiator improved the situation.

It had a minimal effect.

I ran the engine until the fan kicked in around 100C and waited to see if it went off again. It did not. The radiator was hot, but after a while I notice whilst feeling the pipes etc, that the top and bottom hoses were hot as well as the tanks on the side of the radiator, but the matrix itself was getting cooler and was just warm?

It is a new uprated matrix, so I am convinced that it is not blocked in any way, but I have not encountered this effect before.

I started looking at the header tank as I could not envisage how it was intended to work. It has hoses to both sides of the radiator as well as the one to the inlet manifold.

My tank is just that, an empty tank with three pipe connections.

I have discover that there should be more to it than that and the hose from the inlet manifold via the thermostat should be piped internally across the header tank to the top hose and have a small cut out in the middle where the otter switch pokes through.

viewtopic.php?f=4&t=2733&p=17921&hilit= ... ank#p17921

https://forums.jag-lovers.com/t/s1-purp ... s/361660/5

https://forums.jag-lovers.com/t/s1-4-2- ... /386383/17


I am now wondering if I need to buy a new header tank with the correct piping and also fall back on the old type of otter switch which would come in at a lower temperature (more head room for AC) and also the new style of switch does not fill this hole in the internal pipe as well as the original, so the hole would leak more into the body of the tank and possibly be less efficient?

Thanks,

Paul

[1954Etype]

Paul, it is the advance and retard you need to check. We had an XK120 where this had failed and caused overheating.

Angus

[paulsco]

Thanks Angus,

The centrifugal advance works fine, but I have had to work on the vacuum advance; the hole at the carb was slightly blocked and the rubber elbow on the front of the vacuum advance canister was letting in air.
Unfortunately it still overheats:-(

Paul

[mtnjag]

If engine timing marks are all properly aligned, your static/initial timing at idle (with vacuum disconnected and plugged at vacuum port) is not excessively retarded from recommended setting, and your mechanical/centrifugal advance works properly (not really an issue idling in the garage if it holds timing) then to me, i dont believe timing would be the issue. Vacuum advance will not come into play here.

[nichmoss]

I'm not sure what set up you have but, for a 3.8:

The header tank shouldn't be an empty container and I believe that is your issue. The water passes through the top hose and you need that to go across the otter switch. If the water is just pouring into the header from the top hose, then it's probably not passing across the otter switch so, the otter is not working correctly.

I'd expect that as the water pours in when the thermostat is open, that it contacts the otter switch sensor and when it reaches the temperature, the otter switches the fan on. Later when the fan has cooled the water, the water pouring across the sensor is cooler and the switch turns the fan off.

Forgetting the generally inaccurate temperature gauge readings have you tried hard wiring the fan to run all the time? If the car doesn't overheat then I'd suspect the header tank not directing the water to correctly contact the sensor. I think this is the conclusion you've already reached but remember not to overfill the system as it will probably blow off some antifreeze and that will look like overheating.

Good luck, Chris

[Tom W]

If your header tank is empty, then that probably explains your overheating problems. The coolant will be bypassing the radiator matrix and only flowing through the right hand tank and back to the water pump.

[paulsco]

Thanks Chris and Tom, that was my thought.

Strange that it worked before. The trouble is I have been altering one thing or another over the period of this rebuild and I cannot remember at what point the problem developed.

It is probably when I fitted the Coolcat type otter switch, which is supposed to be 85/80C, but I have seen posts where people have said it comes in around 90C.

This combined with my empty header tank quite possibly pushes it over the top.

I am in the process of reverting to a standard otter switch and a few other things, at this stage short of the expense of a new header tank to see if these help.

I know eventually I will have to bite the bullet and buy a new tank though. The expense being that I don’t want a steel one :-(

Thanks,

Paul

[pinza]

Paul,
Here’s some suggestions from my mechanic :

I would ask a few questions .
1 . Thermostat orientation - is it in the correct way?
2. Does heater work ?
3.if car was in my shop I would remover thermostat then replace the housing and fill cooling system .remove water pump belt .then start the engine . Then look into overflow tank while someone kept the rpm at about 1500rpm . Watching for small bubbles in the expansion tank .

Depending on the outcome that test eliminates a internal engine problem .

I’m thinking he has air in the system .

Hope this helps,
Glenn

[Philk]

I started looking at the header tank as I could not envisage how it was intended to work. It has hoses to both sides of the radiator as well as the one to the inlet manifold.

Can you post a picture of your Header Tank & Radiator connections? On my 3.8, the Header Tank should simply have two connections (apart from the overflow vent hose). Looking front-on, the Left-Hand pipe goes to the Inlet Manifold and the Right-Hand hose goes to the radiator (see photo below) There will always be water in it (to an inch or so below the top of the tank).

[mtnjag]

I looked back and while i didn’t see where the car is specified he does sign off a couple of times with a 65 FHC So i assume thats the car. 65 has the 4.2 with a different hose setup, a third hose to the right rad tank.

Whether or not the switch turns the fan on at 85 or 100 the engine should cool with an adequate fan. IMO the Coolcat fan is adequate.

[mtnjag]

You could try a few of the mentioned suggestions at the same time and maybe get to a cleaner baseline. Have an assistant help out. Sounds a little involved but really pretty simple. I did this on another 60s car, not a Jag, that had a similar problem. Problem turned out to be a faulty temp sending unit AND an air bubble stuck somewhere in the system. Finally cleared the bubble and put in a THIRD sending unit and got an accurate reading. (That being said I have never had a problem purging air from the system of my 62 3.8 by simply filling and topping up.)

-Run the front of the car up on some short ramps/blocks to get the front of the eng/car elevated.
-Remove your thermostat unless you know it to be working properly by a visual test on your stove with a known accurate meter. It begins to open at it’s rated temp and is fully open about apprx 6-8 degrees C above that. They have a tolerance like everything else.
-Take the known accurate (stove test) Digital meter temp probe and slip it under the hose and up into the coolant flow of the thermostat outflow pipe. I have a Klein meter, $45, with a thin wire probe that can be clamped tight under a hose with no leaks. Get the end, thermocouple, up into the flow. Don’t clamp the thermocouple. Put it in a location where your assistant can watch the meter and the temp gauge at the same time. He can report.
-Place a piece of cardboard in front of the radiator and run the fan without the eng running.
It should hold the carboard to the front of the heat exchangers. *******Remove cardboard*******.
-Open your heater valve.
-Have your rad cap conveniently ready to cap the tank.
-Fill header tank about half way.
-Place a large jug or better a clean oil drain pan on floor with your overflow hose in/over it.
-Be ready with more coolant that you can conveniently add, funnel is handy here, while engine is running while being able to view inside the header tank for level. Cozy up in the wheel well.
-Have the assistant start the eng, note fluid level.
-Add to bring back up to about halfway.
-Bring eng up to about 1500-2000rpm. I believe you’ll see coolant level drop. This is what I have seen.
-Add coolant as eng runs at the higher rpm and warms.
-Keep adding, don’t let it overflow, and cap it immediately when it appears it will overflow.
-As you run the eng you may see bubbles of air coming out of the eng at this point. Normal if not of an eruptive nature. You’re purging the system.
-It will start puking into the oil drain pan. You won’t see it but it will puke coolant and air, hopefully.
-Bring it up to temp on your known accurate Digital meter. I would go to 100 if you are using a coolant product and then shut down if it doesn’t cool off.
-I think this will do a few things for you:
-Help get any air out of the system
-Confirm fan is drawing “adequate” air THROUGH the heat exchangers.
-Fully filled the system, as long as you got all the air out which may or may not be the case but should be close.
-My 3.8 system runs “full” COLD slightly above the center baffle plate of the header tank.
-Verify the operation of the thermostat and either you used it if operating properly or removed and eliminated it as a variable.
-Verified or discounted the accuracy of the car’s temp reading (gauge or sending unit), and know exactly what your temp is at that outflow location.
-Know at what related temp the fan switch closes. In a full tank it will be fully surrounded by coolant flowing from the engine.

If you suspect you may have a combustion leak into the coolant passage causing heating you can use a simple instrument that checks that. You run the car for the specified time and suck some coolant from the radiator into the device. The solution the device contains will turn color if it finds CO I believe. A significant leak will result in volcanic eruptions, this test will determine if you have a smaller leak. The ones I have used require the addition of the test solution for each test.

I hope you find this helpful. It may not ID the problem but it may eliminate some possible subjects. Others here are more experienced and may take exception, no problem.
Good luck.