What is the correct running temperature for these cars? I run about 186°F, although my service manual says it should be lower. More so around 160°F-165°F. So is 18x°F acceptable? Or should I adjust my thermostat/get a new one to make it run cooler? Answers would be greatly appreciated.

 

Mine runs close to that temp, (a little cooler) but I don't think you're going to run into any problems.
However, something as cheap and easy to replace as the thermostat I would go ahead and do anyways. I mean you can get a thermostat and gasket for under ten dollars and have it replaced in a few minutes.

 

186 F is a fairly common thermostat temp for allot of cars including the jag. mine run slightly hotter then that at just under 90 C which is about 195 F. its good practice to replace a thermostat anyway as stellar worrior said but that it seems fine. my handbook recommended 90 C as the optimal temp but warned not to let it get much higher. if your worried or live in a warm climate put a 82 C or 78C in to keep it a bit cooler and give you some lead way. it is quite important for the fuel injection system that its close to 90 however as this effects fuel economy.

regards jay

 

Hmmmmm. I am currently working through the long list of fun things that may cause the infamous lumpy idle. Being at the right temperature is one of them..... I am showing 72°C at the top hose and 66°C measured at the bottom hose by IR gun.

My temperature gauge is also reading about 70°C. It never gets anywhere near the middle of the gauge.

I think I'm running a bit on the cold side......

Me thinks a new thermostat is on the horizon.

 

oh definitely, my jag always runs smoother when it gets up to temp (85c)
I imagine if the engine isn't allowed to run at optimal running temperature that's probably one of the biggest issues. new thermostat for sure.

sarc, how is your ignition system? anything been replaced on that?

a pertronix coil and distributor will work wonders on a lumpy idle.

 

So where are you on your temperature gauge ? Just to the right of 90?

Funny you should mention that....... I spent a long time reading the forums last night and ordered the very contraption you referred to based on yours and a few others positive feedback. I also ordered t stat, gasket, plugs, plug leads, oil filler gasket, dipstick gasket and a lot of vacuum line. Guess what I'm doing at the weekend :-)

I did have one question on the presence of vacuum leaks or not....... I read on another post highlighted by Doug that if you suddenly decelerate at around 60MPH, your trip computer instant mileage should momentarily read 99...... mine jumps, but only to about 50 or 60......... does this mean I have a vacuum leak ?

I turned the idle mixture screw all the way in (clockwise) and that improved things quite a bit. I have also noticed I have a slight blow in one of my exhausts which is amplifying the lumpyness. I'll temporarily patch, but will probably end up putting on a new piece at some point.

As you can see from my signature, this isn't my first Jaguar rodeo, but so far I have to say this old girl has been one of the most satisfying cars to acquire and fettle with :-)

 

Just to chime in, after having rough idling to the point to killing the engine at stop lights and over extended idles, I replaced a few vacuum and hose lines as well as the fuel pressure regulator, fuel filter, and air filter after doing an AFM cleaning which cleared up the problem substantially (really like night and day, I'm sure it could be smoother now even but compared to what it was, improvement was drastic). Did all of that for under $180 in parts.

On the running temperature, I was also considering installing a lower temp (180F/82C) thermostat as I believed mine to be running a bit hot (showing ~95C in 95F ambient temp. after a 150mile+ 80mph drive in Central Texas) but around town on a nice day (>80F ambiant temp, lighter driving) it gets to the usual 90C and sticks there perfectly. Granted, these are demanding cooling conditions but since it's only May, they are only going to get more demanding.

Would moving to a slightly lower than currently installed temp create any noticeable improvement in cooling under these higher demands or should I just be satisfied that the current cooling system seems to be working perfectly in optimal to fair conditions and consider the 5 degree Celsius increase under high temp./highway driving inevitable and harmless?

Considering the car's age, other problems, and location/season, a pre-emptive thermostat change is inevitable, just deciding to keep the old temp or move down slightly.

 

As soon as my car heats up, it stays just below the green, in the center of the gauge slightly to the left of the 90 degree mark. once there the temperature doesn't falter, just remains constant, and runs smooth.

When I went to replace my thermostat last year the temperature jumped all over the place. I opened up the housing to find NO thermostat, NO gasket, and rotten heater hose all over. whoever was the previous owner of my jag had some interesting ideas on "maintenance" the jag was running too cold and would stall, the coolant was dripping all over the distributer and making one goopy mess, so basically everything got replaced.

My idle now is silky smooth, but when I first purchased it last July it would hardly stay running without babying it.

To get from "barely running" to "silky smooth" this was the process: brand new battery, tighten belts, clean grounds and terminals, changed oil and filter, installed k&n air filter, fuel filter, new spark plugs and leads, new coil, new thermostat and gasket, replaced rotten hoses, installed pertronix distributor includes cap and rotor, and I gutted the catalytic converter.

My horse power sky rocketed, my fuel economy just about doubled, and I now have a very reliable and smooth daily driver.

 

well sarc, I'd say that's a very good indicator that you have a vacuum leak, mine will hit 99. I know the instantaneous gas mileage system on the trip computer is all run off vacuum lines, and all that, but that's it, sorry I don't know specifically what to look for, or exactly how the system operates, but I'm sure someone does haha

 

@stellar

Great, thanks for the tips. I suspected the temp gauge should sit around 90 seeing as that is the middle of the gauge.

Also good to know I will have a way to confirm that I have improved my vacuum situation by monitoring the instant mpg on the trip computer

@john

Always nice to hear another member has been in the same hole and was able to dig themselves out of it. I am convinced these cars can be reliable daily drivers. I never thought I'd say this about a Jaguar, but apart from the Heat & A/C system, I think these cars are "simple", or at least a lot more simple than a V12. I am certified to say that as I also have a V12 :-)

To be honest, my idle is really not that bad. If I hadn't read the forums so much I probably wouldn't have noticed it, however, a lot of the fixes for this symptom are just generally good things to do when you get a new car, so I'm going to go after it as a goal. It will also be a good process to get to know the car a bit better. As you said, all of this maintenance is relatively cheap. I have been pleasantly surprised at how available and cheap parts are for the Series III

 

My '86 XJ6 runs right on 90C when warmed up and the needle barely moves any.

 

So far my Series III sits juuuust under the 90c mark. Not much movement at all. The engine runs a lot smoother when it's up to temperature.

 

Good, that's just what you want.



Does it seem like it's over-fueling? If so, there are some known fixes.

Cheers
DD

 

Good! Count your blessings :-)


Cheers
DD

 

Just curious still, does any have any experience installing a slightly lower than usual temp. thermostat to relieve naturally induced extreme temperature conditions (highway speeds in the modern summer in Central Texas 98F+ average outside temperature; road temps up to 115F)?

Everything is currently operational (running 90C average steady in usual driving circumstances) but the coming summer is sure to be demanding and I'm curious is preventative action here might have helped anyone in the past?

 

I see no reason to change thermostats.

Hopefully your cooling system will handle the conditions you describe and you'll continue seeing a consistant 90ºF on your gauge. If it does, there's obviously no reason to go to a lower thermostat

If the temp climbs higher than 90ºC then either the system is being over-taxed or there's a correctble fault. Either way, installing a lower rated thermostat won't help...as the best a thermostat can do is be fully open at its rated temperature. If the temps climb above the control range of the thermostat then, obviously, the thermostat can't bring the temp down.

In other words, if the system is running (let's say) 100ºC it won't matter if you have the standard 88ºC thermostat or the lower 82ºC thermostat because the prevailing coolant temp is beyond thermostat control range either way

Cheer
DD

 

Well the idle is lumpy even when the engine is up to temp. However, I still have the exhaust blowing by the manifold-to-exhaust connection so I'm only going to attempt tuning once that is fixed. (Waiting for my sister-in-law in London to send the gaskets to me).