I have just replaced a cataytic converter after one collapsed. I have stripped the whole exhaust system down and removed all the bits of cat from it (and removed the back boxes as the rattled a lot). When I refilled the coolant after putting the N/S cat back on, following the JTIS instructions I topped it up, waited a few mins to bleed, turned on the engine and sat waiting for the coolant fans to kick in which didn't happen. The temp gauge moved nicely to half then stopped. A few mins later the bottom hose blew off.

The Thermostat seems to be working as the rad, top and bottom hoses are hot.

I have checked fuse 12 and 14 in the front N/S box (I think these are the fan fuses?) and I have visually checked the fan relay (looks fine, all connections as they should be)

I have removed and tested the coolant temperature sensor which seems to be working fine.

Upon trying for the MOT, the Lambda reading (from both tailpipe exists) is high (1.1 ish) which lead me to think the coolant temp sensor. I am just about to brave the snow to check for leaks in the exhaust which could cause this.

Any ideas why the coolant fan wont kick in???

Thanks so much for any help, i'm really struggling now!

 

In weather like this you'll be waiting a long time for the cooling fans to kick in at idle, with outside temps around freezing point.

As the cooling system problem only seems to have started since you replaced the cat & re-filled the cooling system, I would suspect you have an airlock in the system. Bleeding the system properly is more than just filling up with coolant when cold with the engine off & then waiting-the system has to be 'burped'.

Normally, you'd start the engine & set the cabin heater controls to full hot-then while the engine is cold & idling, leave the expansion tank cap off & as the water level slowly drops, top it up again. Keep doing this until the hoses start to feel warm & then put the cap back on again to avoid getting scalded by hot coolant when the engine is fully warmed up.

Let the engine warm up fully, then switch off & let it cool down overnight. Next morning, recheck the coolant level again & top up as required.

The system bleeds air best with the engine running as the water pump circulates the coolant, carrying any trapped air around the system until it eventually finds it's way to the expansion tank & then vented to air-at which point the coolant level will drop again & you add more coolant.

It can take a couple of days & engine warm-ups before all the trapped air is circulated around the system & vented.

A high lambda number >1 means a weak mixture with excess oxygen, so you may have an inlet air leak somewhere or the O2 sensors may be faulty-although these would throw up fault codes & illuminate the EML light.

 

Thanks for the advise, I have ran it up today to check the exhaust for leaks while on ramps and the interior was blowing cold with a hot engine so I suspect you are right and there is an airlock. I will bleed it again tomorrow once it is back on its wheels.

I did wonder if weather would prevent the fans from kicking in...

Exhaust has slight leaks so it will be worth refitting. I will check for air leaks on the metered input side now. No EML light, so I guess the car is happy with the lambda sensors.

 

I am having a terrible time with my JAG overheating. It only does it on street driving, not on the freeway. We have replaced the water pump, the thermostat housing, the radiator, the thermostat, the bypass hose, and the water distribution pipe.
The car still overheats after more than 5 mins on the streets, but will be fine for 45 mins(up to 2 hrs) on the freeway.
The check engine light has also come on.
Any advice on what else it could possibly be? I am thinking I will have to go to a dealership, which I hate, as being a woman, I feel that I'm taken advantage of.
Thank you for your time.
Joey
Jag S Type 2000

 

I'm not familiar with the S-Type, but have you checked to see if the cooling fans are working when the engine overheats?

If a car overheats when stationary or in slow-moving traffic & is fine when on the freeway, that is usually something to do with the cooling fans not operating.

If the Check Engine light has come on, you can check the fault codes yourself by buying a cheap Fault Code Reader & plugging it into the diagnostic socket. I bought an Autel Maxiscan MS300 scanner for around $30 & I keep it in my car glovebox.

Use the scanner to read the stored fault codes & then post them back on here-we can cross-refer them online to the Jaguar fault code tables & then get a better idea of the fault.

When the engine overheats in slow traffic, can you keep it cool by opening the windows, turning the heater up to maximum hot & then turning the fan blower motor to maximum speed?