I was just going through some old posts which reminded me I should change my thermostats. As I pulled my old ones out (installed by my trusty mechanic when I first got the car) I noticed they had no jiggle pins or air breather holes. I purchased a new set with the jiggle pins and lower 82 C temp.
I was reading an article to make sure to measure the distance to the spigot opening and measure and to make sure the t’stats will open that far to cover the distance. 41mm to the spigot. Armed with my heat sensor gun , a pot of water and a measuring tape. I’m happy to report if you need some good t’stats the ones I’ve posted are good. They cracked open at 82 C and fully opened around 90C to cover the 41mm distance and close the bypass port.
The car runs about 1/4” below the N temp gauge and about 15C difference between the top and bottom radiator hose. (Which I’ll probably recheck).
Just trying to establish what is normal operating temp for the car and for the temp gauge that’s in it.
I can recommend these t’stats as a good replacement (no affiliation)
I understand not all t’stats are created equal and won’t open all the way. Not good for a
V-12.
about a year ago, there was a great write up here that someone did measuring all kinds of thermostats.
I went with 82C/180F Gates thermostats that closes enough, but I had to drill a hole as there was no jiggle pin.
It runs a ‘bit’ cooler than I want, but 90C/195F is a bit warmer than I want. I wish they had 185F or 190F thermostats that fit our V12s! (My reasoning, I’ve measured temperature rise during post-shutdown. The heat soak usually peaks in 15 minutes, and I’ve seen my coolant rise 20F, from 180F at shutdown to 200F. Running a 195F thermostat could easily see a shutdown at 210F, I’d be afraid of a heat soak above 220F.)
But I seem to get the best idle at about 190F. C’est La Vie.
Good point Greg, if I understand correctly and what I witnessed is they crack open at the 82C and not fully open until around 90C.
My idle seems a little off (according to spec.) when cold about 900 rpm and when hot around 600 rpm not 750 rpm. It seems fine but I might have to rebuild the AAV valve as my next project.
I’m fairly meticulous about heat soak, after a good hard run I crack the bonnet open once I hit my neighbour hood and fling it wide open once I’m in the garage.
That’s why I chose the cooler thermostat, so I could just shut down and forget about it About the ONLY issues for me by running a cooler thermostat - my gas mileage suffers 2mpg, and like I said, it idles a wee bit smoother at 190F. But it idles very well at 180F too. And yes, 180F is plenty warm for the ECU to get out of warm up mode.
My 1988 XJS in Park is 900-1000RPM when cold, and 800-850RPM when warm. In Drive, it is about 700RPM. That is all within the 750-850rpm spec in Park. I prefer a little higher -when I set my idle in Park to 750RPM, the idle in Drive dropped to 600RPM, which is a little lower than I like. It just ‘feels’ too low, and the smoothness is better at 700rpm.
If your AAV was faulty, you would be getting the opposite, too high of an RPM, especially when warm.
Double check your timing, I advanced my timing a wee bit above normal which raised the idle RPM. Had to use the idle screw a bit on the AAV to bring it down. Maybe your idle screw is just too much in, or the timing is a bit too retarded?
In fact, how is your vacuum advance? That is key to getting a higher idle…If I pull my vacuum hose to the distributor’s advance, the idle will drop a good 200rpm.
One other thing to check for too low of an RPM, a blocked PCV valve will drop an idle a good 200rpm.
More good points Greg. Funny I never concern myself about gas mileage when I’m driving a V-12 , but you sound like you’re on top of it.
I did turn my AAV valve adjustment screw and it didn’t make any difference which makes me thinks I should look t it. Jonas looks like he has a nice rebuild kit.
I’m probably posting some redundant issues here but I’ve been out of the forum loop and just getting the car back on the road. Probably still the experts thinking these topics have all been covered but probably some newbies to the forum might not know what to ask to get an XJ-S on the road so they can go into the archives and know what to look for information wise.
Thanks again I’ll check into the timing .
I’ve had my XjS for two years now, i was a complete Newbie back then.
I still have a lot to learn, but this forum and a lot of hard work has taught me so much about how this car works! I almost feel like an expert (level 1/10)
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
The Jaguar V12 would happily idle at 300. The problem with doing so is that it doesn’t turn the water pump or the belt-driven fan fast enough and you could develop engine temp issues if stuck in traffic or some such. It also doesn’t drive the A/C compressor fast enough so you could develop some driver temp issues.
Good point Kirby, I never even thought of that.
I have been stuck in stop and go traffic with no issues, but I would still like to get it sorted out.
I think the AAV valve is the culprit. I’ve tried the adjustment screw with no joy.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
9
If the adjustment screw does nothing, I think the passages in the AAV or the plumbing to/from it have to be plugged up.
I’m fairly certain the plumbing to the AAV is good. I was thinking the wax bulb or rusty spring in there. If it’s the passage way is it just a matter of soaking it In solvent?
Anyway I just took these pictures about an hour ago got and cold idle. They almost seem spot on.
I cleaned up the sump tank on the weekend. It seemed to clear up the stumble perhaps it was affecting the idle speed as well. Duh!
About the ONLY issues for me by running a cooler thermostat - my gas mileage suffers 2mpg, and like I said, it idles a wee bit smoother at 190F. But it idles very well at 180F too. And yes, 180F is plenty warm for the ECU to get out of warm up mode.
