I am replacing thermostats on my '72 V12 E. I thought I would try the 74 C original Jaguar brand “waxstat” thermostat. It doesn’t have the “jiggle” hole, so no air bleed. Should I drill a hole or not? I figure Jag knows more that I but, it has the notation “Top” on it at 12 O’clock position but no air bleed hole or jiggle valve at 1 O’clock. Drill baby drill or not?
On my 6-cyl I found it difficult to fill the coolant without a hole there… maybe the V12 is different. Since I live in a warm climate I didn’t mind giving up whatever quick heater performance would be associated with adding that hole.
The purpose of the jiggle valve is to allow air out of the system on iniital fill ONLY. Once the system is properly filled, it serves no purpose whatsoever. That said, starting a V12 with a partially filled water jacket is taking a chance. It’s especially important on a V12 E, because the system fills from the bottom and pushes air up, so it’s possible that you would start with an empty block. Since there’s no bleed, you can drill a tiny hole at whatever point will be at 12 o’clock. Not more than 1/16". Rim or poppet, it doesn’t matter where.
Thanks to you both! Since I only changed the thermostats and didn’t empty the system I only lost about 3/4 gallons. I refilled the header and ran it with the cap off for a bit to get any air out of system and capped it. I’ll recheck the level in the morning. The 82 C ones I replaced had the jiggle valves so I was just wondering and have read some drill it. The advice will come in handy more so next week though as I plan to swap to a Ron Davis aluminum radiator. Thanks again
Michael,
I just realized you wrote the article Jaguar E-Type Series 3 Thermostat!
I read it a number of times to educate myself and then chose the Jaguar Brand C28067 @ 74C. Thanks again for the great info.
If the thermostats have no weep holes, you can leave the cap off for a very long time and not get all the air out of the system. The V12 system is a bit confusing: the header tank communicates with the fitting on the lower radiator hose. The high air bleed is in the radiator upper tank. So when the thermostats are closed, air in the block and head is trapped behind the closed thermostats, and has no way to reach the header tank. At some point, you maybe get lucky and the thermostats get hot enough to open, which would release the trapped air. But that’s going to happen after the heads are too hot.
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Got it…I will re do and drill 1/16th hole in thermostat ridge tomorrow and install at 12 O’clock. Luckily got two extra gaskets just in case I redid them. I did put in the 74Cs to open sooner. I’ll run it a little this am with an eye to the temp gauge. Thanks again Michael for all your generous info/help!
FYI…I have always used Permatex Copper and this time am trying Hylomar Blue. I’ll see how that works but so far, not too happy with stuff. It dries too fast (I mean seconds) and gets lumpy. I know it gets good reviews but…I have never had a problem with Perm Copper on my boat engine or cars. .
A method I have heard of but never tried is to get the thermostat open in hot water and before it can close prop it open with an aspirin. The idea is that the opening will allow air to escape during filling but then the pill will dissolve once the coolant gets to it.
A bit complex compared to just drilling a hole though.
Ive had my V12 over 20 years…always have a weep hole no matter what and the only other thing i do when I refill the system is to start it up and pull the left hand side header hose off. As soon as you get a steady stream of water, put it back on and you should be good to go. JS
Yabbut… the CHALLENGE!!!
Aspirin is a great idea but might it cause a distortion or bend the poppet shaft? I figure I’ll just drill the 1/16th hole next week and be done with it. I also have usually driven the car on ramps to raise the nose hoping any remaining air comes out header tank.
FYI…drove the car this am on the freeway and then surface streets with long stop lights. The 74C thermostat definitely helped lower temp and kept it there while driving. "But…since the new thermostats open at a lower temp (74C) it would cool the engine earlier but once hot (open) the engine temp is then dependent on the fans, radiator, water pump circulation…right? Maybe the other 82C thermostats were going bad?
Hi there Wiggles. I’m guessing by challenge you mean the flange metal is very hard to drill?
I’ll follow your tip Jeff. Pull L header tank hose off until steady stream and re-attach.
No, it’s not, and no, my sarcasm is sometimes too abstruse.,…
You got me. But you are right…it seems to be more of a “challenge” on this car than just pouring anti freeze in a hole in a radiator. 
What is the temp rating of your otter /fan switch?
I was running 74C stats and it STILL ran much hotter than desired. Long story short, it turned out that my otter switch was rated 92-87C. That means the fans only switches on when THE COLD SIDE of the radiator reaches 92C!!! By this time coolant temp coming out of the engine is well over 100C!!
I have now fitted a 72-68 fan switch and NOW the engine runs nice and cool (a fraction below N) in stop/start traffic WITH AC ON.
Hi Philip, I have the otter switch in but I by pass it. I have it direct to ignition switch. When key is on the fans turn on. I have VW Jetta Fans which are 6 blade fans and a motor is a direct fit into round housing. Today mine ran between O and R with the 74C when it used to run almost at the A and the A at stops.
I may be reading too much into some comments re thermostat spec temp…and operating temp…but here goes: IF your cooling system is in such fine condition that it could-would allow your coolant to run BELOW the thermostat spec temp…then…in operation…(exclude warm up)…the thermostat will cycle constantly open and close…to maintain the coolant at the thermostat spec temp…so in that perfect system…if your engine is designed to run its best at 76C…then you’d want a 76C stat. IF…your cooling system is such that your system will run at say 84C…then it matters little if you have a 76C or 72C or 68C thermostat…it will just open at that temp, and stay open…and won’t LOWER your op temp. Nick
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Seems logical and that is why I think one or both Waxstat 82C thermostats were going bad, not opening enough and holding back water flow as the temp is definitely lower with the 74C. The last time I changed the thermostats had to be 10 years ago.