Hello All!

I'm nearing the end of my X305's major mechanical refresh and I'm finally getting around to the cooling system. Before I started, I didn't have any overheating issues, but I just wanted to run through the system to make it reliable for running through the desert in the coming years.

A Jaguar specialist in 6.0 XJSs mentioned that he likes installing step-colder thermostats, for cars where he works (Florida) and for those living in the desert SW. So I ordered a pair of thermostats from him, and to my surprise he sent me the 74 degree ones! The ones I removed from my car were the original 88 degree units and I'm beginning to doubt whether or not the 74 degree ones will talk nice with the ECU (longer, richer warm up times are a bit of a concern in terms of increased engine wear).

Does anyone have experience running 74 degree thermostats in their X305? Should I play it safe and re-install my working, 28-year-old 88 degree ones?

 

There was a PDF doc on someone calibrating the thermostat open dimension vs. hot water bath in stages before the some C degree point

The thermostat is matched to have a couple of degrees above the closed loop mode temp tripping point what ever it is for the V - 12

Other then the thermostat you can verify the high fan mode works through the fan control module being tricked, this does not test the temp switches on the radiator

Do you have 2 radiator fans of the same size , I'm not clear on the years for the 2 fans of different sizes

 

G'day Swagger,

Ever since I bought my car I have had problems with various thermostats, one that was in the car when I got it was installed a bit skewed and couldn't possibly have functioned correctly. Others failed not long after being installed. I have tried several different temp thermostats but it seems that they all pretty much run wide open as the general running temp, according to my OBD reader, is around 90degC. At the moment I seem to have two correctly funtioning thermostats but am unsure of the temp rating.

The electric cooling fans have always continued to run after the car has been shutdown. The fans come on at 86degC lo speed and 100degC hi speed.

I replaced my radiator with an all alloy one sometime ago as the plastic hose spigots on the original radiator were collapsing with age and temp though that made no difference to the running temp as read on the OBD reader.

I don't appear to have an overheating problem with my car but as much as I have searched I can not find any info re the actual running temp of our cars and it would be interesting to compare Jag data with my car.

All this is not much help to you just a bit of background info.

Chees,
Jeff


P.S. The thermostat from the specs in the manual should open at 88degC and be fully open between 93.5 and 96 degC

 

I can't say that a lower temp thermostat would have any beneficial effect. Although with 74C units it could be detrimental. If it floats your boat, you could go with 82C or so, but that becomes a pretty small difference, and next thing you know, you have another "which oil" thread! I don't really like the idea of 74C units.

So, which oil are you using??

I've always run with original 88s, and apparently without issues. Driving on cooler days, say 80F or below, I often find my low cooling fans don't want or need to run.

Looking forward to a list of upgrades and restorations benefiting The Plum.

 

I don't have any experience of this for the XJ12 but on my 750li (E66), I swapped out the standard 102 thermostat for a 90 degree thermostat as the BMW standard temp is insane and cooks all the plastics and rubber seals after a few years and blows the expansion tank once it begins to perish between the two halves. I found fuel economy dipped by a few mpg but apart from that was a good mod. Standard temps were between 90 and 98 degrees in a tropical climate. My feeling is that 74 will be too low for the XJ12. If 82 or 86 exist, I'd experiment around there.

 

Noted!

I just ordered another set of new 88 degree OEM ones (I figure if @SleekJag12 hasn't had issues with cooling in Phoenix, then they must be sufficient). I went ahead and reinstalled the old ones for the time being as I have to get the car running and off my dad's lift by the end of the week and the new 'stats won't be here in time for that. Once I fly back to Cali in August, I'll throw them in before it's planned 1500 mile road trip! I'll also be installing an all aluminum radiator as I was able to get my hands on one (not easy nor cheap!) and with a complement of all new cooling hoses and a brand new water pump, my cooling system should be set for years to come.

As with everything in this car, just stick with what the factory did!

And to divulge, I run Castrol GTX High Mileage 10W-40 mixed with not one but TWO entire bottles of Lucas Oil Stabilizer. Sounds weird, but a friend of mine whose owned at least a dozen XJSs and XJ12s does this with every one and then pairs that with running through a full tank of gas mixed with THREE (!) bottles of Seafoam. He claims they run significantly better after doing this and then he just continues to run 2 bottles of Lucas Oil Stabilizer with every oil change. Seems odd but he's never seen an engine issue and all of his seem to react well to this procedure, so I shall perform it to my car!

 

First priority for the bearings is lubricant and cooling and not a stabilizer

The stabilizer will be in a carrier of lubricant of unknow nature, but you reduce the known lubricant

I use a Rislone product in the oil that has toluene in it , at least back in the days that I saw made a big noticeable difference on a Ford 302 with hydraulic lifters

The Rislone instructions where to install it 500 miles befoer oil change and not be in the system at all times after oil change

You my not see issues until 25 , 50 , 100 K miles but by then it's too late

I knew a guy that would tap his spark plugs on the concrete before installing for good luck as he would tell me , me not knowing your adviser

I do not have the V - 12

 

I'd like to make a quick correction to my previous statement on my oil usage (unrelated to the thermostats lol)

When I purchased the car I immediately changed it with Castrol GTX 20W-50 and have been running that since. I was intending to switch over to the 10W-40 + Lucas formula my friend reccomended, but after Parker 7's post and some further internet research about Lucas oil stabilizer, I've decided against it. Being a low-mileage engine in excellent health, I think it might be unnecessary to deviate from the factory recommendation (much like the thermostats!) and I'll be sticking with good old Castrol 20W-50

Now I've got two bottles of this stuff...oh well. Maybe they'll be of some use in my BMW E28's M30 with god knows how many miles hahaha.

 

In a prior oil change, I tried Lucas oil stabilizer. My goal was to make the engine run smoother and quieter. I did not notice any difference.

Next oil change, I added some ZDDP product, with the same goal in mind. I did not notice any difference. I only added about 6oz of this product, since I am not working within technical data parameters. I'm guesstimating. Modern oils still have some ZDDP, but less than they used to. Some data can be found on the oil websites. With 11 quarts of oil, I don't think I over added.

The Lucas product probably has some ZDDP, but their data for that is a secret. Why is this Lucas stuff so thick? Its like pouring honey into your crankcase.

So on topic, with your cooling system not only totally new but improved with a new radiator, you will have no problem at all with cooling. You might want to put a bead of epoxy around the expansion tank seam for reinforcement. Though they are usually sturdy.

I have removed the side hood/fender seals and replaced with black trim, leaving a small gap along the sides of the hood. It improves airflow through the engine compartment. It helps with heat soak relief. I "feel" like it is a good idea in the desert heat.

 

Has any one had experience running without the engine driven fan or converted to an electric fan ? That big engine unit must suck up some power?

 

The X300 series does not have a coolant over temp light