Hi Everyone,
I live in Australia and my 420G has endless problems in the summer months with getting too hot. The temperature here can get well above 40°C and as soon as I hit traffic or am stationary for too long the car gets way too hot.
At the moment the car has an original radiator with 2 12" thermal fans.
What kind of set ups does everyone else have?
regards,
Here it is. My 1968 420G. This morning the temperature gauge reached the red line.
A 420G should be well able to handle 40°C.
I would address and fix the overheating problem, and not try to modify car to mask the cause of your overheating symptoms.
Invariably the main problem with an overheating XK engine is that over the past 50 years your cooling system efficiency will have deteriorated by a buildup of internal sludge and scale, and indeed past owners may have aggravated this by inappropriate modifications/wrong parts. There is a very profitable after-market industry that tries to promote extra-cost add-ons/modifications rather than actually fixing the cause of your overheating problems.
I would start by giving your entire cooling system a very very thorough clean-out including radiator, block and heating-system, and not just a superficial clean, and look for ANY modifications already done, with a view of returning everything back to factory original specifications, and make sure everything is working properly – factory fans, thermostat, radiator-air-flow sealing etc.
Roger Payne
Canberra
Yes the radiator does look a bit old, might re-core it for a start. I have been in stop start traffic for an hour and it didn’t handle it at all. What coolant should be in it?
I have always simply used a good quality/brand but basic anti-freeze/anti-boil, more for the anti-corrosive benefits and thus no scale-build-up, rather than the freeze/boil aspect so usually ordinary CASTROL Anti-freeze/anti-boil as readily available. And don’t use dam water (not joking – common in country Australia), use good tap-water (but not in Adelaide), no real need to buy bottled/filtered water, depending where you live.
Its only more modern/exotic cooling systems as introduced with the XJ and XK V8s that need anything more special, but don’t buy the Kmart/Supermarket products, little more than coloured water.
If your radiator is clogged/sludgy, so too will be your block and heating system – thus you need to thoroughly clean everything in one go. If you just clean radiator, then it will still re-block up, from muck in rest of cooling system moving around.
Roger
It is truly a beautiful example! Is that Regency Red or another colour?
Callum Terry;
I agree with Roger’s suggestion, make sure the radiator is clean and the block is clean.
I took my radiator to a radiator shop and they rodded it (I think that is the term) and it did not need a new core as the rodding cleaned the tubes. I had my engine out so I removed all plugs and cleaned the water passages in the block and around the cylinders with a power washer and removed a lot of sediment and even a couple of pieces of old casting remains that had to be there since the engine was cast. Since reassembling and driving for a thousand miles in all temps the car runs cool.
Since your engine is still in the car, when you remove the radiator then remove the thermostat and lower hose and use a ‘garden hose’ to flush the cooling system, back and forth, back and forth. I think you will be surprised what you get out. I don’t think you will need special chemicals.
Regards, Joel.
Let’s slow down. First if "overheating’ is simply your view of the temp gauge you may not be overheating but simply have a bad reading. Determine if you are in fact overheating–read the temp and compare to your temp gauge.
Second the 420 G handles that temp (40c) and more but uses the entire radiator. Your two fans probably required the removal of the shroud that pulls from the entire surface. As suggested return to stock fan and shroud.
I run a completely stock system with factory AC and the absolute highest reading I have ever seen was @95c after a very long drive in 40c weather and inserted directly into a traffic jam (with AC on the entire time).
Finally I would check that the radiator cap on your expansion tank is proper poundage and working. Your car looks like it has had a few modifications. Perhaps they were better at cosmetics than mechanical items.
You mention that you have twin electric fans. Are they contained in a shroud? Not sure what should be on the car from new, I know my ‘S’ was fitted with one from new. The shroud ensures that all the radiator surface has air drawn through the fins. If the fans are open then the only effective cooling when stationery is in the area covered by the blades.
On the coolant side of things I would use a 33.3% antifreeze 66.7% water mix (OCD on the % points) You don’t need the antifreeze side of things and the lower concentrations will supply the anti corrosion required
apparently this mix is slightly more efficient as coolant than 50/50
the 420G has a shrouded viscous metal fan, same as a S1 XJ6, but they are NLA,
and later Jag viscous plastic fans need an adaptor and are very tight space wise,
consequently electrics are sometimes fitted, however the WP snout-rad gap is <70mm, so not easy to find a suitable single (thin but high enough CFM)
In Australia, twin shrouded 12" fans from AU-BA Falcons are suitable and cheap, but shroud trim needed to clear WP snout
Consider the possibility of an underlying tuning issue. If timing is retarded due to ignition advance set improperly, or advance mechanisms (vacuum and mechanical) not working, this can be the root cause of overheating that owners chase with cooling system enhancements.
I recieved a new water pump for XK recently that had twice the specified clearance from the impeller to the housing - another possibility to consider.
I’m also in favour of physical cleaning of the system, especially rodding of radiator tubes before going further.
Has the thermostat been replaced yet?
Cheers,
Simon
Kalgoorlie
I had awful hot running issues on both the 6 and 12 classic Jags. I had a high flow radiator core fitted that has 30% more tubes. Massive improvement. I addition it is really important that the cap holds pressure otherwise you WILL boil. So many fail the pressure test due to silt under the seal or just clapped out. A tester for both the cooling system and cap is a fantastic purchase. These two issues are critical on todays fuel.
Also, newer fans that mount directly on the back and front of the radiator are extremely important additions. I had major overheating issues in DC. Now I sit in DC traffic with the a.c. blowing full blast and the top down with absolutely no problem.
I had tried an expensive oil cooler, tuning, better radiator, but the modern fans cured the problem.
Yes I also substituted multi blade fans on my V12 E and added one on my XK.
I did try to dispense with the belt driven 12 blade fan on the XK but the
dynamo charging system couldn’t handle the load and battery would go flat.I
reinstated the 12 blade and use the additional electric fan in traffic or
automatically after it has been parked up.
The electic fans also help move the air under the bonnet and relieve fuel
vaporisation issues especially on the V12.