Cause of overheating after new radiator install

Hi All, 1990 v12 XJS
I have been fiddling with the cooling system, multiple radiator caps , then new header tank due to neck not sealing with cap . Radiator was probably the cause of overheating I was told by shop. Old one looked bad.
So installed a new aluminum radiator, Whizzard cooling , with gano filters on each top hose . Also a filter in heater hose and a bleeder T. Car was running way cooler and and had tested the system to hold pressure well. Before that I bled the system according to protocol twice ) nose up , heater on , airbleed screw open on top of radiator.
One week later I am going to my smog appointment , got stuck in traffic , and my car overheats !!!
I checked under hood , so the driver side ganofilter has no radior fluid in it , but the passenger side is full of fluid. Car was towed home , defeat ! So I checked my Ganofilter on driverside: it is not clooged,
I am thinking thermostat has failed , but wanted your opinions

Mechanic didn’t replace thermostats along with a new radiator?!

Also, how are your fans? Sitting in traffic, even a new radiator will not help if your fans aren’t pulling air enough.

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Make sure they are the correct thermostats and we’re fitted with the breather up.

Thermostat failure not likely; you have to blow both of them to overheat.

I’d wanna know why there’s no fluid in the driver’s side Gano filter. That should never happen.

Maybe didn’t flush the system when pulling the old radiator?

According to the Gano filter description, an empty filter indicates low coolant level, but that probably is for single coolant line systems (not our V12s). When I added two similar filters for the first time, I had some coolant in the driver filter and a full passenger side after first coolant fill. So I topped off the coolant, ran to temperature and watched to see if the thermostats opened and for coolant flow. After two times of doing that I now have both sides with full filters. My assumption was that the atmospheric tank took a couple of times to get the right levels and that would seem to affect the driver side the most, but that’s just a guess.

I think I would agree with @gregma that if you’re sitting in traffic you’ve gotta have the fans working to pull the air. I’d also agree with @Kirbert that both sides would have to have no coolant, even with one thermistat failed in the closed state you’ still have some flow.

My game plan would be to add coolant (looking for leaks) and while doing that checking that my fans come on at the expected temps and also keeping an eye on the filters to see if the thermostats open at the expected temp (my thermostats open at 180). If the fans don’t come on, I’d check the wire connections that coulda gotten messed up during the radiator swap and then the temp sensor that runs the aux fan and belt to see if it’s turning the primary fan (my primary fan is electric so if you have that then check those connections and sensor).

If you don’t have a temp gauge in your coolant lines then I’d get an infrared gauge to check as the barrel gauge isn’t a good guide.

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OK , not to sound like I’m disagreeing with what you’re saying here but if I understand Kirby correctly our responses are not dealing with the immediate problem. I believe Kirby is suggesting that you should not see a filter that is dry and not have coolant running through it at some level at least?
I would suggest that if the original radiator was pulled and the original owner went with the stop leak theory then you could have some blockage at the coolant rail or within the head. That all being said , you can install Gano filters ( personally I dontrust them) until the cows come home. If you pull the old radiator, flush the whole system, replace all the hoses, replace the t’stats and replace the temp auxiliary fan switch and you should be good to go. I did it with the original system, not a problem.

I would refill and bleed the system, also make sure that the banjo bolt and air purge tubing isn’t blocked. Verify that the fan clutch (mechanical fan) works; if the original change it- if working you should hear the fan roar at any engine speed above idle for the first few minutes of driving regardless of temperature. Make sure the electric fan works by connecting the 2 wires together on the sensor in the lower hose. Make double sure that the hose going from the degassing tank to the atmospheric tank has coolant in it and that the atmospheric tank is half full. If overfull, you have a bad pressure cap and if the hose is empty, make sure you can blow air into it and hear bubbling in the atmospheric tank. If you can, you may have a bad secondary seal on the tank cap. I am betting you had an air pocket because of one of the above causes.

I’ve refilled my V12 cooling system several times now, never an air pocket. Engine off. I lift up the front of the car, but put the jack more on the driver’s side so the Left side is a bit higher than the right. I unscrew the bleeder valve on top driver’s side of radiator. I open the Tee valve I installed at upper heater hose. I fill up the header tank (the long one on drivers side). I cap it. I then slowly fill the system at the crossover pipe until I see coolant coming out of Tee valve at heater. I close it off. I keep slowly filling until I see coolant come out of bleeder valve at radiator. I close it, and cap the crossover pipe. I then go for a drive getting it to full temp.

In the morning, I open the cap on crossover pipe. Usually needs a bit of coolant. I’ll squeeze the upper radiator hoses to make bubbles come up and add even more coolant.

I’ll do this over about 3-5 days, usually adding about a few cups of coolant at a time. Until finally one morning I see a little bit of coolant on the ground under driver side fender, where the overflow tank is hidden.

I don’t have the tee in the heater hose; not necessary if everything is working correctly. The heater bleeds itself as the the one side connects to the water pump suction side. You are correct as far as to the rest of the bleeding. It is unnecessary to check the crossover more than once; all you are doing is breaking the vacuum that draws coolant back from the atmospheric tank. If you see coolant on the ground at the atmospheric tank, it is overfull.

I would look at two things, the right stats, I posted photos of the stats not closing the bypass ports and allowing coolant to remain in the engine and by pass the radiator. I showed photos of this, and the GATES brand being the only new ones that opened far enough to work as designed. If they are wrong your car will always over heat in traffic. Then with good double action stats the clutch fan and electric fan need to work and the baffling that separates the two fans needs to seal between the two fans. The electric fan has two rubber flaps that must suck closed when the electric fan is running. If they are old and stiff they must be replaced to get the electric fan to pull air from the front.
I show a mod that assures the double action stats seal the bypass and how to mount a SPAL bad a** electric fan with its own high amp relay. After refilling I drive the car and every mourning check and fill the expansion tank on the left side. It usually takes about 3-4 days to fill. This car has been a daily driver for 12 years except when down for repairs. The biggest issue I think was getting the right stats in the car, but the rest of system must be working properly.

94 XJS 6.0L

Did I get it backwards? I top off at the cap at the crossover, thinking taking the cap off the header tank on the left side breaks vacuum. So we should always top off at header tank?

I think the header tank catches/traps more air.

Motorad” high-flow thermostats

this was the stat descussion.

Greg, I believe that the crossover is the correct point to recheck the coolant after you have serviced the cooling system. At least that is what the manuals tell me

Yes indeed.
By checking at the header tank you always introduce some air in the system.
And if you take a closer look you will see that the header tank cap is slightly lower than the crossover cap.

Removing either cap breaks the vacuum. Raise left front of car, then remove the degassing tank cap and the left radiator bleed plug; fill at the crossover until both overflow, then install tank cap. loosely install bleed plug, fill crossover until 2" below cap and reinstall cap. Run engine leaving bleed plug loose until coolant has no bubbles around threads, then tighten plug. Let cool over night and top off crossover until 2" below filler. Never had an issue with air.

jag 1990 xjs v12
May have solved my overheating problem .So for now it looks like my fan clutch is gone. After idling car for 10 minutes and making a "funny " sound, my fan stopped spinning, Yes, it has been rubbing a little bit ,( trying to adjust fan shroud). When cold it spins when turning, so not seized per say,
so hunting for new fan clutch, fan or go electric fan ?? not much space in V12

New clutch will be faster, cheaper, and easier. If you still have the yellow fan, change it at the same time.

Some like electric fans, but you’d need to modify or get a new shroud. If you have a smallish alternator, and electric fan takes quite a bit of current, so it might max out the alternator.

Get a new fan clutch and a black fan, if your fan is not black already. Lots of good info on both if you run a search. Electric fans can certainly be done, that was my solution, but IMHO they are not something you want to pay a mechanic to do unless you have a great mechanic and deep pockets.

Hayden 2665 Standard