So, after overhauling my cooling system with all new hoses, belts, and thermostats, I drove the car for approximately two weeks before it overheated again. The issue turned out to be faulty thermostats so I ended up replacing them with Stant 180 degree units. However after that it still overheats and there appears to be no coolant going into the heater core. I've tried everything to bleed cooling system including an expensive lisle funnel but I can't seem to get it to behave. Any advice is much appreciated, I'm losing faith in my ability to get this car on the road again.

 

Have you cleaned out the condenser and oil radiator fins and replaced the radiator?
When bleeding the system, do you set the aircon system to defrost?
How do you know it is overheating?

 

Thank you for the reply Greg, however my car does not have a condenser, or any other AC components for that matter. None of it was in anything resembling good shape so it was removed to be replaced at a later date. However I have not replaced the radiator as up until recently the car acted fine. I did clean out the radiator and oil cooler fins when I replaced the water pump this summer though. When I bleed the system I do set the HVAC system to defrost, and I established that the car is overheating due to the gauge reading high on the N or occasionally cresting it although I've always promptly shut it down to prevent damage so I'm unsure how far it would really go. I rule out gauge issues simply because the car has a brand new temperature sensor installed when I did the thermostats. I also got boiling at the LH thermostat when I attempted to bleed the system with the cooling system funnel. It seemed to work well for a while, then the level rose dramatically in the funnel and on shutdown it was boiling from that thermostat which means to me that there was an air pocket which shut the thermostat, however I could be wrong.

 

Few things.

Have the stats got a bleed hole at the 12 o'clock position. NOT a jiggle pin, an actual hole in the disc of the stat?

When you sorted the stat issue, did you drain the steel header tank, the one in the engine bay, as it does NOT drain when the system is drained, and if there is coolant in that tank when you are attempting a near 100% engine drain, it WILL NOT bleed, no matter what you throw at it.

Is the heater tap actually defaulting to fully open with NO vac, as in the arm is in the down position.

Is the heater Inlet hose, the one from the tap, fitted to the Bottom spigot, and was the heater core flushed (garden hose is fine) when the hoses were off.

Is the header tank pressure cap actually "blowing off" at the spec stamped into it.
Is the filler spout cap upper seal intact, so it seals that spout to the outside world 100%. NOT the pressure seal, that has zero to do with it, the actual seal under the top bit you grip to remove said cap.

I have NEVER run any V12 to bleed the system, it just is not needed if you fill it properly.

It MUST be filled SLOWLY, heater tap vac line OFF, radiator bleed plug OUT. I use a 1ltr container, with the BIG supply some 20 steps away on the bench. Pour in the 1ltr, walk back to the bench, walk back to the car, and LISTEN for any "gurgling". If its quiet, pour in that 1ltr, if its still "gurgling" WAIT, then add the next ltr, and so on until the coolant flows out of the header tank spout, cap it, continue with the 1ltr, until the raditor bleed hole "bleeds", fit the plug, continue some more until the filler spout is full, cap that, jobs done.

 

FORGOT, it happens.

Is the atmospheric tank clean of MUD, and the hose from the header tank TO the atmospheric tank CLEAN, most important that sucker. The system will NOT work as designed if that is clogged.

Read my sticky at the top, its all in there.

The stat attachment might also help you.

 

Hotrod, You wrote above:
"and I established that the car is overheating due to the gauge reading high on the N or occasionally cresting it although I've always promptly shut it down to prevent damage so I'm unsure how far it would really go. I rule out gauge issues simply because the car has a brand new temperature sensor installed when I did the thermostats."
If your gauge is at or around the N then overheating is almost certainly not happening. More likely your new sender has a different range of resistance than the old one did!

 

Now this is interesting, I'd never seen that method mentioned before but I am more than willing to drain the system and try that, it may be my next course of action.

I will have to check on my atmospheric tank, I remembered the book mentioning it, but it didn't make sense. I know that the hose, which I took to just dump on the ground somewhere off the fender tank is clear as I blew air through it with absolutely no restriction.

Thank you so much for the information though Grant, I am curious as to why the overflow tank being full would prevent the system from bleeding, but I'm more than happy to drain the system to square one and fill it again to rule out that issue.

 

Greg, my jag normal running heat is gage half to three quarters between C and bottom of N.
I once had a coolant leak and the gage got to bottom of N and it was starting to over heat.
Changed all 12 hoses and it never got to the bottom of the N even in 110 degree Summer heat with air on.
What is normal for one Jag is not really normal for another, they seem to all have different personalities.

 

MAAAAATE, we need a beer, after 12 noon here, getting tempting.

You have done VERY WELL, and I mean that.

The mud clears a lot now with that new info.

The header tank:

There is a hose from the top of the cross pipe that works around the front and enters the header tank at about the 1/2 way mark. This is the FILL hose for that header tank, and also allows the system to purge air as it is filled. BUT, if there is fluid in that tank, air cannot purge, and there is then air locks all over the place. This I found by simply "hard work" trying to sort my 1st HE. When you fill it slowly, air leaves the engine via that hose and into that tank, and then as the fluid level rises, fluid travels that hose, and fills that tank, hence the SLOW fill, it simply takes time.
ALSO, my beer fridge is between the car and the bench, about the 10 step mark, so there is a method in my madness after all.

Atmospheric tank:

It requires to be clean, and 1/2 full of fresh coolant. When the system heats up, coolant travels to the atmospheric via that small hose. When the system cools down, fluid returns to the system, via that same hose. BUT, if that atmospheric tank is low on coolant, the system will suck air, and you are back to where you started. This return of fluid is 100% reliant on both the caps 100% sealing the system to the outside world, as air is easier to "suck" than coolant.
ALL my HE cars purged approx 600ml - 1ltr, cold to operating temp.

Pressure caps:

MONGREL on any day, and new does not mean OK, SADLY. I had access to a pressure tester, with cap adapter, back in those days, and thats when I found my new 15lb blowing off at 4lb, and the remaining stock (30+) at work were way out of spec also. Best you can do, is thumb and fingers, and compress that spring. 15lb will be a strong squeeze for the average hand.

The PreHE was sooooooo simple. Fill it via the header tank, which had a spigot out the bottom, that connected to the bottom hose, and that filled the system via the bottom rad hose, and pushed the air out as it went.

As Greg has mentioned, at or just topping the N, is not overheating. BUT, if the rise continues, then there is an issue. Gauge sender units have always been fickle, and few ohms here, and a few ohms there, never really worry the manufacturers that much. I had some real strange senders for temp gauge back in the Series cars days, and simply fiddled around until I had one as close as I could get it, the joys of working in Aftermarket Spare Parts has its advantages.

The main issue is the stats, and the length of them, and that took me months to find, cost me HEAPS before I fell over that fiasco.

 

If my jag heat gage had ever got to the top of N she would be toast now.

 

We must remeber, these gauges, ANY OF them, are just a GUIDE.

OK, Engine Temp has been drummed into all of us over the years.

I used an aftermarket Temp gauge, with the sender in the available port at the rear of the A Bank heaad, and drove around. Co-pilot wrote down the readings as requested, and the position of the Jag gauge.

I cannot find that scribble, but I do remember at 220F, MY CAR was just topping the N. THATS MY CAR, nobody elses car.
On the highway during our many Interstate jaunts, the temp gauge (JAG) sat clearly below the N.
Around town, just ON the lower lip of the N.

The "knowing" of what that car did was peace of mind for me. It allowed me to fully enjoy the car, and worry less.

Same with the other gauges, all out quite a bit when compared to a Master Gauge, and thats Jag Life, ENJOY.

 

I do so agree with Grant's latest post. On my car i used a remote temperature gizmo with the K probes taped to the top hoses. The difference between the gauge just below the N (89C) and halfway up to the H (97C) on my car is 8 degrees C. As Grant made clear this is not necessarily a guide to your car.
I tested this carefully because I have an on at 90 off at 85 thermostat in the water pump inlet controlling my (main) electric fan, and I was worried that the car would be too hot in traffic before it kicked in. Turns out no bother at all, and when my 27 amp SPAL kicks in, I can watch, car stationary, as the gauge comes down. Now if I changed my sender unit, no doubt the OEM gauge readings would change.

 

I agree, the stock barrel gauge's just aren't accurate. I've had two different brands of temp gauges through the years, SW & Auto Meter/AM (present, plus the stock gauge). Sensors mounted in water rails. In short , when my barrel gauge reads "lower middle N" the two AM gauge's read 215F. That's IMO, worst conditions, Florida's heat & traffic

 

THIS IS AN OLD THREAD.

Thermal gun highest reading at different areas on motor and hoses is 210 degrees and needle is at the bottom of (N), heater dash vent is 92 degrees, ambient temp 45 degrees. Is this normal?
New thermostats are 180 degrees.

 

Well, with work and all I have been too busy to spend much time on the XJS. However I filled it tonight as per instructions and noticed that air came out of the bleed hole and all that good stuff, I haven't taken her for a drive yet, but I did run it to temperature idling in my parking lot. It appears by my IR thermometer that the bottom of the N on the new sender is approximately 190 degrees Fahrenheit. However I'm concerned that one of my new thermostats may be junk since I'm seeing about 20 degrees difference from the left bank to the right bank, 170 to 190. I also discovered tonight that while I worked on this car, at some point I neglected to tighten the hose clamps to the air rail on top of the core support. Hopefully that is part of the problem. It's in the mid to low 30's here and it's getting a bit rough working on the car outside.

 

Small update, created a pressure bleeder to see if the heater core was empty, simply forced coolant through the core, then out the fill neck, then I capped the fill neck and pushed through the catch tank, then moved on to the bleeder with the same process never releasing all the pressure on the system. I took the car for a drive, approximately 5 miles, the car came up to temp, fluctuated a bit at first, then leveled off, at approximately 2 needle widths below N. The blowers came on indicating that the coolant in the heater matrix inlet was up to correct temperature however there was no heat from the vents, and the return line was cold. I'm going to take that as confirmation that my heater core has met it's untimely end. However, I'll take that in the face of the fact that the car is no longer overheating on the same drive that had it nuclear when this whole fiasco started. There may be more work to do to get her to 100%, but I'm closer now than I was before.

 

BEER O'CLOCK, well done.

The heater core possibly only has an air lock, even after all you have done, they are fickle on a good day.

Not up to speed of all you have done, but a quick reverse flush of that core may dislodge the mud plug. Quite common.

 

Well. A small update for those interested. As it turns out my problem is a blown head gasket. I'd used the car sparingly since my last post since my area has been cold and miserably covered in snow. Today it was nice so I decided to go for a drive. She developed a rather severe miss part way through and got hot. I pulled into a gas station and popped the hood to poke around. The oil cap tells the tale. A nice vanilla milkshake on a lovely Tuesday. I'm going to have to take some time to consider my options here, lump or replacement engine. Neither seems particularly appealing if I'm to be honest.

 

My 89' car has a heater core return hose that goes down to that lower rad connection point, would it be worth it to have the header tank also dump coolant into that same lower 'return' line? This same return heater line also has my spin-on coolant filter so it's already hacked up with brass fittings etc it wouldn't be hard to do.

 

Vancouver
You cannot do it piecemeal, I am pretty sure, as the HE coolant circuit relies on various flows to purge the radiator etc etc. You can do it, but it requires a wholesale re-jig; the most important part of which is somehow installing a header tank higher then the engine/radiator, as was done by the factory in the saloons. I have done this, but I did not have the ABS unit in the way, so the header tank location was doable. Without the header tank being the highest point, the feed from the OEM header to the return pipe would not work effectively. What I did was to:

• Install header tank by the bulkhead (firewall) with the main system feed going straight down to the heater return pipe (moved the washer bottle to the wing where the OEM overflow bottle used to be).
• Remove the radtop bleed pipe and make a bleed takeoff from the LHS plug to the header tank (all going uphill)
• Replace the cross pipe with a spoutless version from the 6 litre saloon (as I had a high point already at the header tank)
• Fitted an overflow tank in the engine bay where the factory header tank used to be
• Bock off the B bank coolant feed to the purge system (the small pipe coming up vertically from the thermostat casting)
• Everything else in the OEM system can be removed.

6 litre saloon cross pipes come up on ebay from time to time, brand new. If you retain your old one, you need to blank off the feed from it to the question mark pipe.

Close up of header tank

The finished system

Close up of header tank feed into T piece in heater return

A simple way that would help the OEM system purge on filling would be to install a bleed T by the heater tap; but you are still stuck with the fact that the radiator cannot bleed easily and would need to be bled from the plug still, on filling. On my system the rad bleeds uphill to the header on filling the system.

Attache is a piece I wrote for a mag about it.