Interesting: wasnt aware of this. Ill look forward to discovering the answer.
Im gonna guess the automotive industry did a metric f—kton of research into this, and didnt make the change willy-nilly.
Ok I may be overly nervous about temp but I just drove 45min at 65-70 mph. 80 degrees outside. IR reading 190 with 190 stats. I like it. Idle 10 min… up to 207 don’t know how high it would have gone. Drove 5 min. 190 again. When running both sides are within a degree or 2. At idle 8-10 degrees difference. Does this sound ok? Or should I put a 350 in it? Just kidding!
William,
You didn’t mention your auxiliary cooling fan. Was that coming on and going off depending on coolant temperature?
Paul
Yes Paul it comes on at 190.
Also has an aluminum radiator. It’s about 5 yrs old with about 3000 mi. on it. Seem to have good flow based on temps while running. Im concerned about a 90 degree day in traffic.
I have a stock radiator that I bought about 10 years ago. Mine never runs that hot (207). Just another data point.
Stats are new but I’m starting to wonder if they are bad or even the wrong ones. I had them installed when I had some other work done. I’m running out of ideas. New relays and sockets a few days ago too.
That sounds about right for 88c (190) thermostats.
88c (190) chermostats will be fully open at 102c (215f) so you are in the range of thermostat control. Also you can check the difference between radiator incoming and outgoing temperatures when standing in trafic. If you have 97c (207) in radiator inlet, then you should get ~ 90c (195) on the radiator outlet (lower hoose). You should have ~6 to 8deg c difference. If you get less, the your fan clutch is getting tired and you should get a new one.
I suspect that this might be due to poor contact somewhere inside the cluster. You get extra resistance with a poor cintact and that’s why your gauge reads low. Do you have issues with other gauges? Also it can be due to poor grounding of instrument cluster. It is a good idea to run aditional ground wire to the cluster.
I had similar issues with my cluster but with fuel gauge. After complete disassembly and full cleaning of all the contacts all gauges started working like never before 
But in general I would say the whole construction of instrument cluster is just asking for trouble…
Do you still have the stock belt-driven fan? Any idea the condition of the clutch? What is your idle speed?
In general, I believe the Jaguar V12 has more trouble keeping its cool at idle than at speed. Bad fan clutch, low idle speed, plugged radiator fins, missing radiator surrounding foam, lots of things can contribute. I suspect one of the main culprits is the design of the impeller in the water pump. The pump is almost identical in configuration to a regular Chevy V8 water pump yet the impeller itself is completely different. The Jaguar impeller has strongly backward-inclined vanes while the Chevy impeller has slightly forward-inclined vanes. I put a Chevy impeller in my Jaguar water pump and had much less trouble with cooling at idle – but I changed a lot of other stuff at the same time so I dunno if the impeller made the difference.
Thanks for all the input! Radiator is aluminum, fans are twin electric, new water pump, new relays and relay sockets, stats are new 190’s. I notice a bit of an air leak between radiator top and the cover. No debris as radiator was pulled 150 miles ago. That’s all I have left to consider. Unless the new stats are not working correctly. I’m only concerned about where the temp might go in 90 degree temps in traffic. I didn’t realize the the stats weren’t fully open till 205-210 degrees. But that’s where the car runs after 10 min at idle when it’s 80 outside. Maybe I’m overly concerned but I’ve been told that’s my nature! Haha! Thanks again for you time I really appreciate it.
I plan to do this when I fab up new water rails. Seems logical to me. Put cooler water on the hottest part and transfer that through the block to extract at pump. Even heat distribution and speedier warmup.
Head temp would be cooler due to more heat transfer available in the coolant introduced there rather than preheated by the block, but system temp should remain the same given same tstats.
As long as it is NOT boiling, yer golden: lack of “headroom” (coolant temps in the 180s) might lead to that, but, if it stays inboiled, you wont hurt anything.
Is it a straightforward swap?
It was, but note that there are LOTS of variations of Chevy water pump. The single most important thing in a centrifugal impeller is the OD: larger makes the pump more powerful. In industrial applications, it is common to shave the OD off a pump impeller to match the flow rate to the application so you don’t waste energy overpumping. In the case of Chevy water pumps, I think you’ll find the larger, more powerful engines have a larger OD on the impeller, and you might WANT that if you’re concerned about flow rates, especially at idle.
Also note that you might be able to address cooling issues at idle by simply installing a smaller pulley on the pump so the pump turns faster.
How many times does this topic come up, and I"ve been there too.
My temp gauge used to sit 3/4 between N and C, when I refurbished my XJS I broke the spade terminal off the gauge sender, so I bought a new sender, with this installed the gauge ran nearly at H, so I pulled the sender out of my spare 6.0L and with this sender installed the gauge runs in the N.
If your cooling system has been serviced with the following addressed then you will not have issues with the car overheating. My car will idle all day in 45°C ambient with AC on no issue.
Radiator re-cored (sounds like yours has been replaced)
Thermostats new and of the correct type (very important as some stats being sold are the wrong length and do not shut off the bypass).
Main fan clutch in good condition.
Pre-Marelli - ignition system in good condition, retarded ignition will cause the engine to run hot.
Thanks Warren. You’re all patient and kind. I’ll change the thermostats. That’s all that’s left to do. Drove an hour last night at freeway speeds car stayed at 180 ish degrees 15 min in stop and go traffic 205 again. Nervous shutting down at that temp. I had a blown head gasket last year that cost a lot to fix. So maybe I’m over cautious. What thermostat brand should I buy to ensure they are the correct length? 180 or 190?
Make sure it has the jiggle pin and that it is located to the top.
True, true…
And this topic will continue to come up. Older cars, questionable grounds, huge (no, make this HUGE) variations in parts quality.
I have done some testing. The OEM sender and a new replacement, will show different “end result” based on this:
That’s actually really good.
Anywhere the temperature matters it is very accurate. Aftermarket is within a few percent.
The whole range from 20C (68F) to 40C (104F) where it is off by over 10 percent, those temperatures do not matter at all.
At 65C (149F) it’s going to read a bit low, but thats still mostly outside the range of interest.
Once you get in the important operating range it’s excellent.
This is what I found when I took measurements on the oil pressure gauge sender too.