In an emergency situation, where the Engine might start to 'over heat' while stuck in a 'traffic jam'.

Would turning on the Heater help to dissapate the Heat away from the Engine and help the Engine run Cooler at least untill you are able to get back on the open road?

(XJS V12)

 

The heater core is just another radiator so in theory it would help but I am not sure to what extent. Sometimes it takes very little to tip running temps over the edge so it stands to reason that there may be times when a little help makes a big difference.

 

I don't know specifically how it would work with our jags (don't completely understand all of the details of the heat/ac system), but I've used that strategy in the past with different vehicles and it did work to some degree. It's not a substitute for fixing the overheating problem but might get you through in the short term.

 

yeah ive heard this before too and often wondered if it works.

I guess the idea is put warm air in your cabin and push the cold air out through the Air Conditioner Radiator, pushing cooler, unwanted air out near the engine. Is that the general gist?

 

As Baxtor stated, the heater is just a small radiator and a fan.If the car is running hot then turning the heater on can help but it can only do so much due to the radiators small size.

If you were in stop-and-go traffic and the needle started to rise then turning on the heater will buy you a little time until you can get the car up to a speed to increase air flow and cool the engine.

Mark

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The answer is yes, Many years ago when I raced MkII Jaguars we would do this for the 5-10 degree difference it would make; could be the difference between boiling and not. Later we got better radiators made; with hind sight just a new rad would have worked wonders.

 

Hi Bro

What prompted my question, was one of your posts when your car started to overheat while you were going up hill.

That's what got me thinking if turning the heater on would make any difference and going by the replies so far, it would seem that it could, even if only just enough to stop the Rad boiling over.

 

That's really handy to know, as last Summer while stuck in a traffic jam, I couldn't take my eyes of the temperature guage and was waiting for the worst to happen.

As I was stuck on top of a bridge, with no where to pull over, in very heavy traffic but the 'Jaguar Gods' were with me and the gauge went up only half way.

 

Sometime a couple of minutes can make all the difference between boiling over or not.

 

+1

 

Any trick to get you out of trouble is always worth knowing.

 

I only hope I never need to try it but last year it was touch and go when stuck in a traffic jam on top of a Bridge, one of the worst places to break down.

 

OB, all good advice.

BUT, your in the UK, it dont get hot there, really.

Mine run just fine in 45c, a/c ON, and city traffic snail pace.

The radiator clean (you know that), the correct length thermostats, working at correct pressure header tank cap, and if still fitted, a GOOD fan hub, and all should be fine.

Mine all have twin thermo (Ford) fans, and that was one of the best conversions I ever did.

 

Hi Grant

I think I can tell that you haven't been to the UK for a while!

As we do get one or two days each year! where its almost too hot to go out and while I was stuck in this traffic jam on one of those two days, I was getting paranoid, that She was about to boil over.

Though the 'Jaguar Gods' were with me and the gauge only went up half was, as the auxillery fan cut in and saved the situation.

 

All quite true about the heater. Also VERY true about electric fans from Grant. There is one point though:

As standard on the XJS, turning on the heater turns on the aircon, so that gives the engine more work to do in traffic. However, turning off the heater turns off the aircon AND turns off the auxiliary fan until the temp rises quite a bit. If you have the mechanical fan (which does practically zero at tickover) the engine gets quite hot - aircon off - before the auxiliary fan activates.

So FWIW, my best solution is:
Like Grant says, do the twin large electric fans mod. But also wire them to be switchable on manually regardless of heater settings, as well as one working automatically whenever the aircon is on, and the other big fan being normally thermostat controlled.

If you have the mechanical fan, a decent solution as long as the mechanical viscous hub is 100%, is to change the OEM fan (very old inefficient type) for the largest and most powerful you can find that will fit the shroud hole. THEN while keeping the OEm wiring, also wire it with a cabin operated manual switch. At the same time, fit an "off switch" to the aircon compressor earth wire, also cabin activated, so if you select "heat" from the system, it WILL function and heat the heater matrix but NOT cool the evaporator.

Then, in a hot coolant scare, this last mode enables you to turn off the aircon but turn ON the aux fan, AND keep the heater going! Then you get (a) extra cooling, (b) no extra engine load and (c) the extra heater matrix radiator cooling!

By the by, under these last circumstances, you should select DEFROST, which calls for MAX heating and over-rides any temp selected.

Greg

 

Nah, never been to your bit of dirt.

I conceded the temps there are different to here by a long stretch.

The Summer here is usually 5 months of 35c and above, with NO let up. In that time about 15 days are above 42c, so we are a boozy mob at best.

Mind you, I am in Sth Aust, "the driest state on the driest contiment", other parts of OZ are different.

Mine has the RH fan thermo wired, and a safety ON inside the cabin that simply switches that fans relay earth terminal. The LH fan is A/C only.

With the A/C on, the LH fan runs constantly, and I have NEVER had the RH fan come on whilst the A/C is ON. The fans are that good.

I also run 82c thermostats, and they are NOT Jaguar stats, they are Ford stats, as the Jaguar units at the time were too short, and did not shut off the by-pass ports, and the engine would/could run hotter than I wanted. This I have written about at length many times, and is freely available on request to your email address.

 

Another yes vote here. It's an old trick.

If your hood is hinged at the front, popping the hood open to the first
safety catch can also help.

 

That scares me Plums. I was driving in traffic when i first got mine and the hood flipped up and i had to stop in the middle of the road in traffic to close it ha ha ha. Funny now but was crapping myself at the time lol!

 

It ain't much different up our way.

When it's hot ,it's hot. If I have ever been in a car nudging "H"(the red Zone) no fan or heater core is going to save you. They stop you getting to the red zone!
I know, I owned an XJ cherokee for 17 years.

Just pull over and let it cool down. Even if you block the slow lane on the busiest highway in NSW on Good Friday for 20 minutes..... yes you might have held up thousands of Easter travellers.(but if you didn't someone else would)

And you don't have a blown head gasket or cracked head or cylinder.

 

Oops, I think I popped it to get your VIN the day you were registering it. It was pretty funny from the passenger seat!