Can somebody describe which is the best method to measure temperatures of the tubings and check temp. differences in order to diagnose a stuck thermostat or clogged radiator on this car (Double Six). Is there a systematic approach? Which tubes? What temp. diff. (approximately) at e.g. a motor coolant temp of 90°C; outside temp of +- 25°C; driving and not driving; Thanks!

 

What I have used, but I have had very little issues, due to my "post purchase" servicing of any car that joins my fleet.

Bonnet open, engine running, maybe 10 minutes, "feel" the top hoses, they should "feel" the same temp, then CAREFULLY reach down and "feel" the bottom hose. It should be cooler. The spec for crossflow radiators in top shape is 15C drop, top to bottom hose.

With 88C stats, the top hose would be somewhere in the region of 95C+/-, so the bottom should be around the 80C mark, if using a thermometer.

If the radiator service history is unknown, or more than 5 years old, remove it, service it, and repeat in 5+ years.

The stats have an average life of 8+/- years, they work hard. Also, there has been a spate of wrong stats supplied, as in too short, so beware.

I know its a S3 V12, BUT, in the XJS section (next one down), at the top, are many stickies that will give you a good path of work.

 

Thanks for info! Dont have car history. What do you mean by servicing the radiator: flushing (is LiquiMoly safe?), US cleaning, opening and rodding? New core?:

 

1st is to remove the radiator.

Visually look over the core, paying attention to the state of the fins, then the tubes, where they attach to the header plates. Any suspect looking areas, take it to the professionals.

I always take mine to the Pro's, and they either tank off refurbish it, or recore it.

If I had to list priorities on a V12, the radiator would may be #1. Overheat a V12, and your bank manager will luv you.

The system is more than capable of doing its task, its just the years of neglect that catch up sooner or later, and the big $$ need to be spent.

 

IGNORE THIS HERE, ANOTHER CRAFT MOMENT, PRESSED THE WRONG TAB.

[QUOTE=Grant Francis;2275345]1st is to remove the radiator.

Visually look over the core, paying attention to the state of the fins, then the tubes, where they attach to the header plates. Any suspect looking areas, take it to the professionals.

I always take mine to the Pro's, and they either tank off refurbish it, or recore it.

If I had to list priorities on a V12, the radiator would may be #1. Overheat a V12, and your bank manager will luv you.

The system is more than capable of doing its task, its just the years of neglect that catch up sooner or later, and the big $$ need to be spent.

 

Thanks for all info!

 

Somebody knows at which temp the thermostatic switch should start the electric fan (and when to stop too)?

 

E-fan switch:

For some reason 94ºC always sticks out in my mind. I think mine triggers a bit sooner than that; maybe 90-92ºC ?

Let's hear what the others have to say

Cheers
DD

 

That switch in the water pump inlet elbow is 85C down here, on all mine.

There are variants, and that would be based on market emissions requirements for the year of the beast. We had near zero emissions until late 1988.

 

Thanks Grant: 85+15 higher at cyl.head. Is'nt that too high to start the fan?

 

NOPE.

The top hose etc temps fluctuate a lot, hence the sensing on most cars in the bottom hose.

100+ 5 or so, maybe a tad more, is NOT going to harm anything. Its when that temp just keeps rising coz the radiator etc is not doing its job that problems arise.

Mine has thermo fans, twin. The RH is thermo, with that switch as the earth trigger.

The LH is A/C only. With the A/C on, and 45C outside, I am cool, and the RH thermo fan NEVER comes on, even in traffic.

I run 82C stats, with 1/8" hole drilled in teh outer disc, and that hole at 12 O'clock when istalled.

I also run a 13psi cap on the header tank, never liked that 15psi, and I got zero issues.

 

CRAFT moment.

If you are running hotter than acceptable when driving down the road, and the radiator etc etc is all OK, take a look on top of the transmission, up in the tunnel. There will be a ratty looking foam sheet, probably sitting ON the transmission, as old age has long ago released the adhesive. This thing will stop good air flow OUT of the engine bay, FACT. Remove it, and I reckon you will notice a huge difference. When the trans is out one day, get some of the "modern" heatshield, like the HotRod boys use, and fix that in there. It is mm's thick, and super good insulation, and simply opens the escape air greatly.

The air can get ON, but if cannot get OUT, there is going to be a problem.

 

you can check radiator without removing it. Disconnect upper and lower hoses, recovering coolant in a container, then use a garden hose at full pressure on each hose port to flush and back flush the radiator until clean water comes out the bottom. If the water flow looks "normal", no stoppage, the radiator must be ok.

 

Thanks every one!

 

The laser pointer heat reader guns are super helpful in stepping round a cooling system to see close to actual temps and temp differences through the radiator. When I got mine it was only $30 on Ebay, probably less now on Ebay or Amazon (unless all the covid measurers sucke them up)

 

Ha! ...My family are amazed I have a temp gun in these times, I told them I’m always prepared!