I’ve searched a bit and haven’t found the answers I assume might be there. Is there a known, reversible mod to run the cooling fans for a few minutes after shutdown until the engine bay cools down a bit after the shutdown engine bay heat spike? (Either by time or temperature) I always felt like this was a tad hard on the plastics and some of the electronics in summer and leaving my hood/bonnet popped isn’t a great fix outside my own garage... Mrs. Peel is a 97 convertible.

 

Leave the key in the II position after you turn off the car. It will keep the fans running until temperatures fall.

 

If you want to do it without having to leave the key in position, I think you'd need to add a secondary temp sensor and some circuitry to run the fans. They're controlled by the car's electronics, rather than directly. The circuit itself just needs a couple of relays and a couple of diodes, so it's not super complicated from that point of view, but I guess Jaguar didn't think it necessary!

 

Not sure of the exact details, but this feature is already built-in from the factory. To my knowledge, if the engine bay is "too hot" when you park the car, the fans run (on high?) for a short time. I assume this is based on coolant temperature. Folks sometimes talk about this feature kicking in as a precursor to larger cooling problems (stuck thermostat, failing water pump, etc.)

As usual, a dose of philosophy is necessary. Jaguar likely specified plastic and rubber components that can withstand this sort of heat under the worst conditions (parking in the summer heat of Death Valley type of thing), but most likely for the benefit of its actual customers within the factory warranty period...

 

seems simple enough to do. Just get a timer relay that allows power to flow for a certain amount of time after the ignition hot as a signal goes off. Wire at the column and pass through the firewall using the same route as Real Gauge. Wire in series with a temperature probe placed wherever you deem appropriate and set to your desired cutoff. This circuit trips a standard relay that sends battery voltage from a good, adequate, constant hot in the engine bay to the fans. I recommend using proper diodes on the original circuit and this new one so that the new system and old do not back feed each other. Keep computers happy.

Timer relays are available at Amazon and other retailers. This is your hard limit on how long they will run. Recommend some testing as to current usage to prevent the battery from being compromised.

I believe that my car has a shutoff run cycle of the fans depending upon temperature.

On cars that definitely do this, the manufacturer must balance battery life over this function for obvious reasons.

BTW: everyone check the nipples on the radiator. They get to a point due to age where they just crumble without giving much of a warning. Before a long trip.

 

Hi,
MY 1996 XK8 cooling fans (radiator fans) always run for around 30 seconds or a little longer in the UK summer (so not hot weather) automatically. In the winter (around 4 degrees Celsius today), the fans shut off when the engine is stopped. This seems to be factory settings in my car. Cheers

 

Yeah, I’d really like to get it to several minutes of cooling after shutdown when hot. Mine don’t run after shutdown to any significant extent, tho they might do the 30 seconds sometimes, I don’t honestly remember..

 

As others have advised, my XK8 cooling fans also always used to run on for a short time after shut down here in the UK where temperatures never reach impressive heights. Whenever I took my Jaguar down to southern Spain, the fans would run for several minutes.

This must be a function of the ECT (Engine Coolant Temperature) Sensor which sends the ECM (Engine Control Module) a signal indicating the temperature of the engine coolant. However, there has to be additional control or switching within the twin fan assembly to activate them ON/OFF as a result. If your engine is not giving any indication of overheating, I think the ECT must be OK and the issue is with the cooland fan assembly.

Graham

 

If you want the fans to run after shutdown, just install a defective thermostat that sticks open. The hot coolant from the engine will continue to circulate into the radiator and the fans will continue to run. Ask me how I know.
But seriously, what good is that anyway? The fans aren't removing heat from the engine bay, they are removing heat from the radiator and putting it INTO the engine bay. Without hood louvers, that heat is just sitting under the hood and cooking everything. Does that make sense to anyone but me?

 

Open the hood and that solves that problem.

 

Or, and this may be overkill, swap on an XKR hood (bonnet) with the louvers and the heat will escape passively.

 

While your point is logical, the heat actually does get pushed out of the engine bay even without bonnet venting. Everything from the trans tunnel to the wheel wells, and the completely open underside are escape points. Yes, heat rises, but if you could place a heat sensing camera in the engine bay, there would be all sorts of air swirls and convection currents.

The XKR vents are for taking heat away from the intake and inter-cooler pipes in the very tight place in which they function. They also serve in theory to prevent air pressure build up from lifting the front of the car at speed.

My car came from the deep south and Texas for the last decade before i purchased it. None of the engine bay plastics show even minor fading nor brittleness. The same is true for the plastic sensor bodies and electrical connectors. The only things that deteriorated were the coil pack wires and jacks, and not terribly so, and the nipples on the original radiator. It was 20 years old.

I have worked on high quality, older, Japanese cars for years and see that this car has no plastic quality issue in comparison, other than the most minor of things in isolated circumstances.

 

For even more overkill, the 'bonnet delete'...

However, in fact, the engine was designed to make temperature quickly and keep it for a long time (*****e.g. Szczupak et al below, the whole thing here is edited from another thread).

Thermal stresses in the aluminium engine are maximized in going between cold to hot to cold, not staying at the design hot, especially if you are going to start the car again soon after stopping it. Everything in the engine is designed to run best at the design temperature range and to get away from cold as fast as possible (there's a Jag patent on this somewhere).

The principal electronic components (the modules and sensors) appear to be surprisingly resilient after ~20 years having been designed for substantial temperature tolerance (e.g. ECM has a tested design tolerance of 100 C). Many of the problems we complain about are destroyed polymers. Yes, those are crispy (have replaced too many connector housings to count now, but the pins and wires are invariably okay), but I would trade this for keeping the engine and it's not clear how much decreasing the temperature post-drive improves the polymer situation since the polymers are breaking down driving heat and with time too.

Jaguar's design decision was to quickly obtain keep the heat, and was made on purpose understanding the principal tradeoffs that kill aluminum engines and with efficient operation.

So, in summary avoiding 'heat soak' is directly at odds with the stated design decisions of Jag, and at odds with an understanding of how aluminum engines are designed and run. Enjoy your 'heat soak', thrive on your 'heat soak', punch the car up to the max coming out of the parking lot a half hour after you put it there. Live...

*****Szczupak D, Brunson D, Carling J, Cooke J, Joyce M, Massey N, White C. The jaguar AJ V8 engine. SAE transactions. 1997 Jan 1:1546-54. (this is widely available with a quick internet search)

 

Yeah, I’ve read this before and I do not find it at all compelling. These engines are almost famously long-lived (once tensioners are sorted) so I personally think worrying about some incidental cooling of the aluminum engine while trying to keep the engine bay cooler after shutoff is a total red herring.

However I feel like we have ample evidence that thinks like breather tubes, power steering hoses, ECUs, etc. all get aged a bit faster from the heat. Having mostly driven very old cars with quite poor parts support, I’m not confident, even with a Jaguar, that some of these plasticy bits will always remain available. So while not an overwhelming concern, it’s on my mind...

Btw, yes, an XKR hood would work very well, tho it might expose one to up-badging shaming and would be a fairly expensive item to get & repaint. Also not sure I will do it but found a Hella time delay relay and a cheap Sensasys preset thermostatic switch that could probably manage what I wanted. I think/suspect it needs to be wired to ground the low speed fan signal wire to the relay but not 100% sure.

As a background to this, if anyone’s wondering, I do rather like the XKR hood. I think that all X100’s would have benefited from it, and I am vaguely noodling on whether or not I want to trade up to an XKR.

Thanks everyone for the replies so far.