Hi Guys
I am new to the Jaguar Forums and have just completed (well I thought i had !) and restoration of my Jaguar Mk2...which has been a huge task given the state it was in !
Having taken it for about a five mile run I had steam coming out of the overflow pipe on the top of the radiator...I flushed and flushed the engine with two different coolant system flushes to no avail, same thing happened on a test drive. I had already fitted a new water pump, all new hoses, and a new thermostat. Tried it again at the weekend without a thermostat at all in it and exactly the same thing...very frustrating! I did a compression test on it which showed a couple of cylinders were down a little on compression compared to the other four. I have tried a headgasket "sniff" test which has proven relatively inconclusive.
I would be very grateful if anyone has any ideas where I should go next apart from a therapist ?!!
Kind regards
Mark

 

You didn't mention the radiator, looks to be blocked up at this point from the info you have provided.

When it over heats, get the palm of you hand on the matrix (it can be done) and I'm betting that it will have cold spots on it; it should feel hot all over.
Cold spots indicate no coolant flow.

About rad flush products, they're more of a preventative measure, if things are cocked up to the point where things are over heating after just 5 miles, they're pretty useless.

A garden hose test doesn't tell a person much either, half the tubes can be blocked and running water through it will still flow and make it appear that it isn't blocked _ when it is.

You said "you restored the car", what about the engine, did you have a machine shop boil/steam clean the block ?
Pistons, valves, head etc.....?
Any coolant in the oil ?

 

Thank you for reply JeffR1, much appreciated. Sorry should have provided more info...the radiator has been off the car and flushed a number of times but only with a hose pipe for 10 mins or so, the top of the radiator gets really hot, must admit not checked the rest of the radiator for cold spots, so will check that 👍
The engine and gearbox have been out, checked and all looked good apart from full service etc. I have set the timing to 10 degrees before tdc and to be fair the car pulls really well. No coolant in the oil, so no white sludge at all.
Couple of things to add also; in the small reservoir at the top of the radiator, there does not look like any 'movement' of water, no bubbles as well... Also, I have just checked this afternoon and the old water pump has the number C14944 stamped on the housing and the new one that I fitted has C15694A stamped on it, could this be the a possible problem ??
Thanks again
Mark

 

First of all C14944 is a cast iron bodied water pump and C15694A has an aluminium body so both will fit and do the same job so this is not you problem.

When you say you say you have steam coming from your over flow pipe this is normal so what does your temperature gauge read?

When I rebuilt me 3.4s engine I had it steam cleaned inside and out. All new parts fitted and a new radiator core but I still had steam coming from the over flow pipe. I have since learnt this is normal and down to over filling the radiator. Water when hot expands and under pressure, and the radiator cap should be 7lb pressure cap, water boils at a lower temp than 100 degrees “C”. So over filling the radiator with water to the top does not allow the water to expand other than out of the over flow pipe and generally as steam. When you check the water level you find that as water has escaped it is low in fact out of sight when looking in the radiator so you fill it to the top and the process starts all over again.

I was frustrated with constantly filling up my radiator as I did not know how low the level was. So a round six years ago I converted my car from Pos to Neg earth and removed the RB340 regulator from the inner wing. This left me with a perfect position to fit an expansion tank. I picked up a brass tank from an MGB and plumbed it in so the over flow steam from the radiator would go the expansion tank when hot and as the engine cools the fluid is sucked back up from the expansion tank to the radiator. In the Six year since I fitted the expansion tank I have not had to top up the radiator and when I do look in the top when the engine is cool the water level is in sight level with the over flow pipe.

The XK engine did not over heat from new or they would all have been recalled so over heating is down to old age, worn parts, clogged up water and oil ways. A good clean well serviced XK engine should not over heat and fitting a Kenlowe fan to the front is like taking pain killers for a broken leg. The leg is still broken you just can’t feel it until you try to run on it again.

 

Hi Cass3958

Thank you for your reply, that is very helpful. Okay, that makes sense regarding the water pump, I was doubting myself that the old pump may have been capable of pushing more water around, so that always that fear !

The gauge starts to climb into the Normal range and slowly but surely rises until I pull over (the gauge is at the top of the Normal range by this point), there is some water coming from the top of radiator over the bonnet and steam out of the overflow pipe. After it's cooled down with the bonnet up, I need to fill the radiator with around a gallon of water. All of the signs of overheating. The radiator cap is a 4 lbs cap that I fitted in line with the Service Manual and Haynes Manual which I changed from a 15 lbs cap that was on it when I bought it.

If I have overfilled the radiator and it starts to blow steam out, would that then keep pulling the water/steam out until its game over ? I guess I am assuming (don't like that word at all !) that once some water had overflowed, it would find its own level and be happy !

Yes, I have seen that many people have gone down the route of an expansion tank, and its good to hear that you have done it and it worked for you after suffering similar issues to mine. I think that might be the way forward before starting any serious engine work...

( Btw that engine bay of yours is a thing of beauty &#128077

Thanks again
Mark

 

Do you have the correct thermostat? It should block the bypass as it opens the flow to the radiator. If it's not correct and doesn't close the bypass route, very little coolant will flow through the radiator.

The thermostat used in the series XJ (and probably in the 340?) doesn't work in a Mk2.

Finding correct thermostats seems to be difficult (or expensive) these days. An alternative is to partially block the bypass using a plug with a small hole.

 

Yes Peter, the thermostat is something that I did consider, and after changing it for a new 'standard' thermostat, I purchased a new 'bellows' type C3731/1W. I have tried to run the car without a thermostat at all, bug that resulted in the same problem manifesting itself !

I have seen the thread suggesting a nylon disc/bar with a small hole to restrict the by-pass which is another option.

I may try the suggestion by Cass3958 by installing an expansion tank, and if that doesn't sort the problem, I think I will try the by-pass restriction option !

Thanks
Mark

 

I would say a 4lb cap is too low and possibly why water is pushing past the rubber seal in to the over flow. 15lb is too high as the pressure might blow out the engine core plugs. I was always told 7 lb C10289 was the correct cap to use. My engine is a 3.4 from 1967 and no different to any other XK engine of a similar year. In my system I have an open cap on the radiator which allows water to flow to the expansion tank which then has a 7 lb spring cap on there.
https://www.sngbarratt.com/English/U...20cap%20Mk2%60

 

A missing thermostat would not cause it to over heat, when I first got my car, I didn't realize it was missing.
We drove it over the mountains, and it would run a little warm going up, and run well below 70 going down.

I'll stick with the blocked rad diagnosis.

 

Mark
There are two areas which need to be addressed for this overheating.

First is have you had a proper test to ensure that you do not have engine compression/exhaust gases in the coolant? This can be done by any reasonable radiator repair place. They use a dye in a container which is placed over the radiator filler cap hole. There may also be a home test kit to do the same thing. A common problem in old XK engines is corrosion in the head which can lead to the sort of problem you are having. Actually judging by the amount of water you have had to put into the system I am prepared to bet this is your problem. I have just gone through this with my current MK1 2.4. (The head was subsequently welded and repaired by a local engine shop.)

Second is your radiator in good order? As Jeff says putting a hose in the radiator doesn't tell if it is really clear. The only sure way is to have a radiator repair place remove the upper and lower tanks and clean out the tubes. I did this and unfortunately my radiator core was beyond repair so I opted to go with an aluminium radiator which cost A$250 versus A$1000+ for a new core. Not concourse but very serviceable.
Cheers

 

Thank you for your replies guys...there is a lot to consider !

I have not tried a 7lbs radiator cap Cass3958 and if I go down the expansion tank route, which I think I will need to do, that would be the way to go with an open cap on the radiator.

My theory Jeff was that if running the car without a thermostat and with no restrictions fixed the problem, then I could discard a blockage in the 'block' (even though its been flushed more times than my septic tank !) concern. Sure enough it changed nothing, so that could still be a problem...I will check the radiator carefully where I can get to it all over today.

Yes Bill, I did a couple of "sniff" tests on the radiator with a home test kit and the colour did not really change very much at all...it could be said it went slightly light blue from a rich blue (that could be because I had the bottom of it too close to the radiator water ??). At best I would say it was inconclusive and I don't live close enough to anywhere to have it professionally tested without it overheating !!
I guess its difficult to know how clear the radiator is without taking it apart and recoring it, or replacing it... It has been flushed along with the whole system probably 20 times including using two lots of off-the-shelf treatments and I understand a hose pipe is not ideal, but it does seem to flow very well... To be fair, the one thing I have not done yet is to try to back flush the system, but there is very little in terms of nasty stuff coming out during a normal flush just a little discolouration and the I have run the hose through everything until it is perfectly clear.

It's really frustrating as she runs really well, at least for about five miles until she overheats !!

Mark

 

My guess woul be with Jeff and a blocked radiator. Coolant cleaning treatments don't work on seriously blocked radiators, especially if a previous owner has used Bar's Leaks, which mixes with sediment to form something resembling cement.

More info: What is the temperature gauge showing as you drive? It may be worth pointing an infra red thermometer at different parts of the radiator and engine. Is it steam coming out of the overflow or hot water? And do you see steam (resembling white smoke) in the exhaust if you prod the throttle when the engine is warmed up? As Bill said, it's the coolant that should be tested for combustion product.

 

I agree Peter, I definitely need to run it up to temperature and check for cold spots on the radiator just in case someone in the past has put that crazy cement stuff in...and given some oc the other things that have been do d on the car, it wouldn't surprise me !!

So, when I take it out of the garage after a couple of minutes I take it off choke (manual switch AED) and take it out on the road...it slowly climbs into the Normal sector...after around 3 miles it continues to rise to the N of Normal and then every minute or so therafter it goes up by another letter of Normal on the instrument dial until I pull over when it hits A of Normal and we have steam from the overflow (and water on the bonnet using the 4lbs radiator cap, just steam when using the 15lbs radiator cap). Then its time to sit around for half an hour or so before filling with a gallon or so of water, and limping home !

I don't have white smoke coming out of the exhaust when I prod the accelerator (although its difficult to see close to exhaust when uding the accelerator!!). I have not seen any white smoke when I prod it relatively hard in the garage when the engine is warm...

 

"Normal" - not particularly relevant, but that isn't a standard Mk2 temperature gauge. It's usually marked 30, 70, 110 Celsius and the normal position is 70 or a shade over.

For the rad cap, they were fitted with 4 or 7 psi; it varied with model and year. The thermostat wasn't suitable for higher pressures. As a result, water pump seals and core plugs are often not rated for higher pressures. I'd not be inclined to go above 7 psi and in a properly working system, there's no need.

 

Well, I didn't realise it had the incorrect temperature gauge Peter...looks like another job for winter ! Think I will invest in a 7lbs radiator cap when I finally figure out the main overheating issue or go down the expansion tank route...

So, I started the car earlier and let it get up to a working temperature just in the 'Normal' sector. The top radiator tank was very hot; the top hose was hot; the bottom radiator tank was very hot; the bottom hose was hot...all good to that point... However, when I held my fingers (difficult to get a palm on it with the fan and shroud in place) on various points on the radiator there were definitely big differences. Some areas were very hot, some were not hot at all (bordering on cold), more so close to the middle and at the bottom of the radiator...this sounds Peter and Jeff like you were spot on, I think we need to take the radiator off and look at getting it tested and a possible re-core.

Thank you so much again guys, this forum is brilliant, very glad I have joined you all !!
Regards
Mark

 

This is an original Temperature gauge fitted to my S Type from 1967 and is the one Peter is referring to as fitted to the Mk2. It is a Smiths gauge.

 

Ah yes, thanks Cass3958, that helps to narrow down my future search...its amazing the small changes on top of others' small changes adds up to big changes over the years !!!

Thanks again
Mark

 

There are new gauges available from the usual suppliers, but I prefer to buy secondhand mainly from ebay. They may need some restoration and swapping of parts, but they are cheaper and more likely to have a correct calibration for the sender.

 

A common misconception is that a radiator must be OK if it passes coolant at the rate it is supplied by the water pump; not so ! The whole point of a radiator is to spread out the coolant over a large surface area so it can give up its heat to the air passing through the radiator. So if a lot of the tubes get blocked over the years the radiator still passes the coolant via the tubes that aren't blocked; it just doesn't get cooled much so the engine overheats.

Another aspect is the depth of the pressure cap seal from the top of the cap. It needs to be a bit longer than the housing that the seal butts up to. Back in the 80s when I rebuilt my Mark2 , there was a case of some people buying caps that seemed to fit but the depth of the seal from the cap top wasn't enough to provide the seal. The cap spring is what provides the pressure rating and if not compressed enough doesn't provide the pressure resistance when the coolant gets up to its correct temperature. So the coolant boils because the pressure cap isn't providing the correct pressure. Some caps I saw provided no pressure at all ! The seal depth was so short, it never got to butting up to the housing ! I actually measured the depths on my radiator and checked the pressure cap I bought to make sure it was goiing to make a seal. I never had any trouble. My car was also a 2.4 reg number RAB 671F. I think it went to Japan, as there is now no record of it on DVLA records

 

That would make sense Fraser...I always 'assumed' (there's that word again !) that if you take the radiator out and flush it with a hose pipe, and water didn't overflow from the top where the hose enters, that it was nice and clear. However, if the water from the hose can get through just enough of the tubes it won't overflow, will appear a fully clear radiator, and yet it may not be hitting all of the tubes (explains my coolish spots on the rad)...therefore not letting enough water through to keep the engine cool enough. This would then also explain why I can travel five or so miles before it overheats.

Also, if it was a blockage in the 'block', I would guess the car would overheat within 1/2 mile or so, unless the restriction in the block is only slight ?

I think I need to get the radiator out of the car, and off to be tested !

Mark