My engine has always run a little cooler than most, well below the "N" because I've been running a high volume electric fan, removed the A/C compressor and cooler, which really made a difference.

But for some reason today the engine started running cooler than usual on my way home this morning. My first thought was it was low on coolant, so I turned the heater on full blast (it blew hot air) and after it cooled down I topped it off. But it wasn't low enough to affect the engine temp. There was no pinging, dieseling or any change in oil pressure and performance. Just a lower reading on the temp gauge, and it was 97 degrees outside!

2 days ago I was low on fuel and stopped at a gas station that only had 90 octane gas. I only filled it half way and when I got into town I filled it the rest of the way with 93. Could lower octane make it run a little cooler? I thought it would be the other way around?

 

Thermostat going faulty? Temperature gauge going faulty or dirty contact.

Might be checking if it's losing coolant and getting a sniifer test done just in case the HG is going.

 

A Jag V12 running cooler than normal in 97ºF ambient temps? I'd be checking the temp gauge. You know how flakey they are.

Just my two cents :-)

Do you have a hand held infra-red thermometer? Take some reading at the thermo housings to get a rough idea of water the temp is and compare to the gauge.

From memory, and FWIW, my V12 was about 180º at the bottom of the N, 195º in the middle, and 200º at the top. A few years ago....7 or 8, really...some of us compared results and posted them on J-L. There was as much as 20º variance in temp gauges

Cheers
DD

 

Oil is clean, no moisture or chocolate milk/foam, and no smoke/steam out of the exhaust.
The thermostats are almost new, I think I've put maybe 1500 miles on since I installed them.
I know I have a very small leak in one of the rubber rings on the head coolant pipes. It's something I keep an eye on, and I check the levels regularly. But this time the level was good.

I was thinking maybe the probe or the contacts were the problem too. I may play with them tomorrow if I get a chance.

 

I WISH I had one of those hand held temp testers...guess I may have to invest in one.

 

Easy investment, it will do the job. There is a new location on Amherst st in Nashua. Let me know if you go, I'll meet you there.

39$

Non-Contact Infrared Laser Thermometer

 

Jamey,

I was going to say that the beast finally bled all its air out, it can take forever to get these bled sometimes.

THEN I read about the dribble from that transfer pipe seal, and NO that cannot be the case, coz it will suck air IN via that seal as soon as it cools down, trust me.

I would guess you got one stat having a "day off", as in being lazy to close that little bit and allow temps to stabilise.

AGREED 100% that in 97f it should be kissing the bottom on the N in suburban running.

The a/c condensor missing would certainly give it heaps better airflow, so maybe that really does have that much effect on the cooling system, and then add the compressor missing also, there is just so much scope for air to get IN and OUT.

Mine has all the luxuries, and twin Ford thermo fans, and at our 50KPH speed limits with the air on (LH fan running), it sits just shy of the N, and the thermo fan (RH) never comes on. That was last time I had it out and it was 39c here. With the air off and a cooler day, the fans do NOT come on at all as long as I am moving forward, and under those conditions the gauge is sitting a good needle thickness below the N.

I run 82c stats with a 2mm hole drilled in the disc, and that hole at 12 o'clock, and they are NON Jag stats, coz I found the Jag ones tooooo short to close the by-pass, but that is another saga.

 

Well it all returned to normal without me doing a thing. I suspect Grant was right once more and it was just a lazy thermostat stuck open.

 

That is quite possible. With a new radiator on the motor way 100kmh my temp cycles noticeably from the bottom of the N down as the stats open and close.

An IR thermometer is a good investment - when taking a reading use the BLACK hose and take note of the distance to spot ratio in the instructions (the distance to hold the therm away from the target) both of these can add significant error with the cheaper units.