2003 JAGUAR s-type 4.2 liter v8. My water pump is leaking. Talked to a mechanic who said that this is common because the impeller is made out of plastic. I found one on rockauto with metal impeller as an upgrade. It will be here Monday and this should be a strait forward install, famous last words. Ok easier than the rack and pinion. what is the best antifreeze to use. will be completely backflushing cooling system

 

Water pumps are not common. So he is wrong there. Be sure and inspect things carefully as there are many plastic pieces on the NA 4.2L cooling system.

Are you 100% sure it's the pump and it's not just leaking in that area? We just don't get many water pump failures.

Now the new 5.0L is well known for bad water pumps. Jaguar has revised that water pump twice so far. But at least that problem is much more minor than the timing chain tensioners that caused so much trouble on the old 4.0L engine!

This is one area the STR is way better. The thermostat housing is all Aluminum.

Always use the factory coolant. For my 2005 STR that is Dex-Cool. Be sure to change the thermostat too. At this late date I would also change any hoses you can get to.

Finally make sure your mechanic is aware that leaning over the motor and resting on the top of the over flow tank will break/crack the plastic nipple.No point in causing more work for yourself!

I know as I broke mine doing just that!
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The coolant`s brand is not that important. Just make sure you use the correct specifiacation. It should be shown on your water coolant reservoir and also in your manual. While you are on the job, check the reservoir for cracks and small leaks.

 

Mechanic showed me were it was leaking from the water pump. Previous owner had a Jaguar shop change the water pump couple years ago. Do suggest that i remove the overflow tank when doing this job. couple years ago i changed a water pump on my N14 cummins learned a valuable lessen make sure mating surfaces are clean very clean think it will take more time accessing pump

 

True, but in the US Dex Cool is the most commonly available.

 

Well I would take the top plastic tank out just to get more working room.

But then every time I do any work I use that to inspect everything in that area. With the top tank removed the front of the engine is now finally accessible.So look at belts, hoses, DCCV stuff that is right in the front of the engine. I like to check idler pulleys and the belt tensioner too.

Might even be a good time to change air filters since the air box needs to be removed.
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I just replaced my water pump on my '03 S Type, 3.0, 77k miles. I used Zerex G-05 coolant, 50/50 pre mixed.
I took apart the failed water pump. I think its the original one, it had a Ford logo in the casting. Anyway, there was a plastic impeller in it, which was okay. The point of failure was at the shaft/ seal. The pump was making an awful noise, then started leaking at the shaft. When I had it out, you can grab the pulley portion and pull up and down, there was alot of play. The impeller itself was not an issue. I did remove the plastic radiator overflow canister, kept it out of harm's way, and gave me more room to work. While I was at it, I replaced the air filter, thermostat, and accessory drive ( serpentine) belt.
I bought an Airtek pump from Rock Auto, $40.00 US shipped, we'll see how long she holds up! Best of luck in your repair!