So, my new car (95 XJS Convert 4.0L), I only really drove it from Baltimore to CT a month ago with no usage since then. Because CT temps were in the 50s today, I thought I would get out just tinker with it . I charged up my dead battery and started with no problem. As I warmed it up,these things I've noticed:

• Idle was 1200-1300
• mechanical fan stayed in high, clutched position, lots of air drawn. Did not quiet down or release clutch at anytime.
• Temp gauge very slow to move and eventually moved just above the blue arc, no further. It was this way driving the 4 hours back home from where I bought the car.
• Upper radiator hose cold
• Recovery tank temp was hot
• Thermostat housing hot to the touch but did not take an actual measurement. I think the sensor with the two pin connector is the ECU temp sensor and the sensor with the single wire is the gauge. Correct me if I'm wrong. ( I did not short the wire to see if needle would swing)
• Inside Heater air was between warm and hot at full hot control (so internal circulation and heater core seems good)
• Idle eventually came down to 800 after blipping the throttle a few times

A slow moving or cold gauge would seem to indicate a stuck open thermostat, but if so, I would not get hot air in the car.
If it were a stuck closed thermostat, then it wold have overheated on the 4 hour journey and while sitting in my driveway today

Can anybody hazard a guess as to what's going on based on the above observations? I'm concerned about the cold upper rad hose.

Thanks

 

I'm a little confused on your testing. You make it sound like you ran it in the driveway for 20 minutes, but on the other hand you mentioned running it for 4 hours? Which is it?

Cold, does the fan free spin or is it locked up?

Have you entertained the possibility that the system has a bunch of air in it?

 

I ran it for 30 minutes today only. The 4 hour trip was last month when I picked up the car.
In the 30 minutes today, the inside of the car began to heat up but the temp gauge indicated very cold, just past the blue arc/square. I didn't run it any longer for two reasons. 1, I am not sure if the gauge or sensor is indicating correctly and didn't want to chance overheating it. 2. It was indicating that way for the 4 hour trip a month ago and at the time I was attributing it to a possible stuck open thermostat or the fact that the fan was locked drawing in colder than normal air when not needed. During that trip the idle stayed mostly at or above 1000 rpms too. Another symptom I thought due to a colder then normal running engine.
I can move the fan but seems more locked than free. Yes, it is possible but the seller did not indicate any coolant maintenance recently. Could I have driven the 4 hours last month with air in the system and it not overheated? But Yes, that is a possibility. Where is a the bleeder screw?
So there you have it

 

Hi C&P

On the 1995 4.0L AJ16 Engine there is a known issue with the 'Throttle Return Spring'

(On The Throttle Body 'Not' the Cable)

The 'Clues are there' You Blipped the Throttle and the Idle went back to 800 RPM

In order to Correct this Jaguar came out with a 'Stronger Throttle Return Spring'

I had a very similar problem on mine

Its a very easy Fix involving a few screws to remove the Original Spring and then replace it with the 'Stronger Throttle Return Spring'

I can't remember the Part Number but I 'Think' it was NBB313AA or NBB313AB

One of those two numbers should be the 'Stronger Throttle Spring' Replacement

Also Check that you haven't got a 'Sticking Throttle Cable' which could be part of the problem

It could be a combination of that and maybe a Stuck Thermostat as well, which could be why the Top Hose isn't Heating up

But make a start by making sure the Throttle Cable is 'Free' and isn't 'Sticking' and 'Bleed All the Air out the Rad' like SS said

There maybe a plug on the Top of the Rad which you can remove to do this to get rid of any 'Air Lock'

Also check for a build up of any Leaves or Debris that may be blocking the Rad Core (just do a Visual Inspection and then report back)

As the Rad Core is very fragile and you don't want to damage it

 

Thanks OB.
Regarding the throttle, I blipped it by hand on the cable cam on the TB, not the gas pedal. By the way, I wanted to check the "throw" or full travel of the pedal vs wide open throttle. At pedal floored (engine off of course), the pedal reaches the downshift button before the throttle is fully opened. I also noticed that there was a lot of free-play of the pedal before the cam engaged the actual throttle shaft. There was a good 1/2 in of cam rotation prior to the cam actually beginning to rotate the shaft. I then made a small adjustment to the cable housing relative to the bracket by loosening the two nuts on either side of the threaded housing end. That got rid of the large fee play but pedal floored still does not give me full throttle. I have heard that some pedals can bend with age effectively hitting the floor before the throttle is fully opened. I looked at the pedal and couldn't really tell if it was bent in anyway. The pedal fulcrum looked pretty substantial. Maybe they were improved in the later cars, maybe not. Still don't have WOT with my pedal.

If it let the butterfly close on its own, it snaps shut pretty hard. That is when it is difficult to open again. I have to really put a good amount of effort to open the throttle. If I gingerly place or help the throttle plate back home, then the next opening of it is much easier. I am sure there is a lot of carbon on the plate and in the bore . I did read it was a known issue about the throttle body/butterfly plate sticking. Some carb cleaner and a stiff acid brush should get rid of the carbon deposits. If I'm ambitious, I'll remove the TB for a good cleaning in the spring. I heard you have to remove an intake pipe for that. Cable seems free from binding.

Regarding the coolant issue, you mentioned the heater core, I am getting heat in the car so I think it's not blocked with leaves and the heater valve is good(looks new) and internal circulation through engine and core are good. The mystery is why the upper Rad hose is cold. the recovery tank is full and gets hot.

EDIT: I just realized you said Rad Core, not heater core. I haven't really taken a good look at the radiator itself. I may have a few issues here like a fan clutch that is not releasing to freewheel which it should very soon after startup. Most cars with mechanical fans, in the winter months, you'll here it loud with full fan engagement and then soon after the clutch releases to a dull whir where the freewheeling starts. This isn't happening to this one. Another reason it's running cold I'm sure.

 

Yeah it sounds like you just need to wipe down the TB and butterfly with a rag and cleaner.

I've never lived up north, so I don't know if 30 minutes would be a crazy time or not for the engine to come up to temp. Don't rely on the temp sensor. Grab a cheapo IR thermometer at harbor freight or the like, so you can compare the temps.

I'd doubt you made a 4 hour drive with essentially air cooling only. Hard to say if there is a tstat issue without knowing whether it was really up to temp, but it seems the gauge or sensor can't currently be relied on.

The heater core will be closed off in the back part of the system, so it is entirely possible to have warm air inside with the thermostat still closed or only partially open.

I also think the single wire sensor should be for the gauge, wouldn't hurt to check that as well, or check the differences in resistance at the sensor.

 

AJ16 stats are a known issue, down here at least, They stick, BUT, the average life of a stat is 5 years, so a cheap simple item to keep on top of.

Sounds like the throttle idle stop screw has been messed with in someones attempt to lower the idle speed. The stepper motor may be full of carbon. This I have read about due to the EGR system a lot pf markets have, we DONT.

As said, clean the inside of the throttle body, reset the disc clearance (0.002" from memory). That will STOP the disc binding in the bore.

Top hose cold, no idea, as your words of description indicate it should be the same temp as the header tank.

Fan clutch is toast, as you probably know.

IF, and thats a huge IF, the engine is running that cold, then the fueling maps etc would all be based on that temp, so idle etc would all be up the creek.

My only hands on with the AJ16 is in the X300, which have twin thermo fans, and they both had partially stuck stats, and weird stuff was going on, mainly in the "R".

 

Regarding the throttle "disc" as you termed it (around here its the butterfly), that is a very good description saying it's "binding in the bore" That's exactly whats happening. I can make it bind more by forcing it closed more by hand. Then it really sticks the next time you try to open it. Is there a procedure for adjusting the stop?
For the top hose, as with any thermostat, it won't open unless it reaches the stated temperature. ...and if the engine doesn't reach the stated temperature, then it won't open and the hose won't be warm. So the question is, the gauge may very well be indicating a cold engine, which if still cold, won't open up the Tstat. If that is the case, why won't the engine warm up? And for arguments sake, if the Tstat were stuck open, then coolant would always be flowing to the upper hose and eventually would/should feel some heat of the warmed up engine, maybe not to the temperature it is supposed to be, but a little warm. Maybe I just didn't run it long enough. But dang, it was 30 minutes and the Tstat housing was quite hot.

 

Hi C&P

With a Stone Cold Engine, that has been left over Night and Not Started at all in the Morning

You should be able to Spin the Fan Blades round with a 'Flick of your Finger, for at least one Full Revolution 'Maybe be more'

If you cannot do that, then it would seem that your Fan Clutch is 'Toast' like 'Grant' has said but if you Can Spin the Blades with you Finger

Then the Fan Clutch 'May' be OK

But this 'Must' Repeat 'Must' be on a Stone Cold Engine that has been left overnight or this Test 'May' be Compromised.

If you can Spin the Fan Blades on a Stone Cold Engine (That is Good!)

If you can't Spin the Fan Blades on a Stone Cold Engine (That is Bad!)

There will be a little resistance, as its not gonna Free Wheel like a 'Fidget Spinner' but one or more Revolutions

With a Good Flick with your Finger 'Should be possible'

When you First Start the Engine and the Oil in the Fan Clutch Starts to 'Heat Up' that is the moment the Fan Clutch gets a 'Grip on the Fan'

At this point the Fan Clutch should Spin the Fan like Crazy and really kick up a Storm of Air enough to Flatten Grass

And this is 'Good' and what you want to happen

At least that is exactly what you want to Start with.........

But you Don't want it Spinning like Crazy all the time........

At a Certain Temperature Point, the Thermostat 'SHOULD OPEN' and if and when it does, then the Water will circulate

To the point where the Engine is running at its optimum running Temperature, for the ambient weather conditions prevailing

At this point the Fan Clutch should start to let go and the Fan should Spin a lot Slower

Though if you were stuck in a Traffic Jam, then it may start to speed up

So what appears to be happening:

Is that your Engine is getting Hot But it is getting Hot in all the Wrong Places!

How come so? Because the 'Thermostat' isn't opening and that is almost certainly why your Engine is Hot while the Top Hose is Cold

In other words what you've got is a Water Circulation Problem caused by a 'duff' Thermostat

'I'm just repeating what 'Grant' said but using a few more words' and 'Grant' is a 'Legend' who knows what he's talking about

So job number one, is go and get a New Thermostat and then see if the 'Fan Clutch' suddenly starts to behave itself or not

And also do the other stuff 'Grant' said 'He's not called the 'Wizard' for nothing, as there is nothing that he doesn't know!

Same applies to 'Greg' These two Guys are 'Legends in their own Lunch breaks'

Also Fix the Sticking Throttle and Accelerator Pedal

You can't drive around like that and enjoy the Car!

Also get a Hand Held 'Laser Thermometer' (I think you guys use Harbor Freight)

One of these is worth its weight in Gold!



Hand held Laser Thermometer 'Worth its weight in Gold'



Hand Held Laser Thermometer

 

OB, thanks for taking the time for that very in depth reply. yes, I believe it is getting hot in all the wrong places but I still can't fathom how I managed to make a 4 hour trip at both highway speeds and sitting traffic without it overheating or blowing a hose if the Tstat were truly stuck closed. So now I m not sure of the chicken or the egg regarding the Tsat or the fan. Is the fan not decoupling because it doesn't feel the radiator hot enough, meaning it is not feeling warm drawn in air? I'm assuming like most fan clutches, there is a bimetallic spring on the front of the clutch that when affected by the temperature of the drawn in air, it ports the oil for the internal clutch....or, is the fan being in "high gear" all the time causing the water to stay cooler than normal, never heating the engine up enough for the Tsat not to make the opening temperature. Of course, both components could just be bad in which I should stop guessing and change both the fan clutch and Tstat.
Oh, and stone cold engine, I cannot free spin the fan blades.

 

Its been a while, and the 2 X300's re tucked away in storage.

There is a stop screw with a locknut on the throttle casting, and I dont remember where it is precisely.

Loosen the locknut, place 0.002" feeler strip between the disc and the bore, SLOWLY turn the screw inwards whilst applying a "tugging" pressure to the feeler, and when that feeler starts to move, STOP. Tighten the locknut, not silly tight, just firm, and thats it.

The idle speed is controlled by the stepper motor, and as I said, will probably be clogged. There is a SET procedure for removing it and refitting it WITHOUT destroying it. I have never had one out, as we dont have EGR systems here, they dont clog up.

There are many threads in the X300 section about that procedure.

The temp thing, same as before. Replace the stat, and the fan clutch, and work onwards from there.
Maybe consider pulling the radiator and getting that cleaned and sorted at this time. It will need to be done sooner than later.
If the coolant level is low, that will need to be investigated and sorted of course.

This all sits in the "catch up" maintenance program I ramble on about constantly with ANY new to me Jaguar.

 

Hi C&P

If you can't Spin the Fan Blades on a 'Stone Cold Engine' Then you need a New Fan Clutch

But you don't need the 'Chicken or the Egg' you need both and you can get a new fan clutch

For about half the price we have to pay in the UK

Also be sure to Check on the Condition of the 'Fan' as these develop 'Stress Cracks' especially round the Hub

Where in the event that it does break up as they have been known to do,

Then it is likely to take out your Rad and put a big dent in your Bonnet/Hood

In any event not to get a New Fan would be 'spoiling the ship for a cents worth of tar' but try and get a 'White' one if you can

Because changing the 'Fan Clutch' is shall we say 'an interesting job'

That you may not want to revisit anytime soon

Very DIY doable but also a little bit awkward

The reason 'you got away with it' on your 4 hour drive, was possibly due to the Temp Gauge probe being deprived of Hot Water

And not giving an accurate read out, of what is going on inside the Engine

And also the 4.0L AJ16 Engine is a bit more forgiving if it gets too hot

Try that on an Alloy V12 and you could come home with a Parts Car!

So lets just say you got lucky!

At least on this occasion.......

 

Carsnplanes - did you ever figure out what was making your throttle plate stick closed and if so, how did you correct it?

 

Hello,
Yes, there is a hidden small set screw on the forward side of the throttle body. Screwing this in or out will adjust the closing gap of the throttle plate/butterfly. It apparently was loose and had backed out of adjustment. This allowed the plate to fully close and lightly jam itself against the bore when allowed to close hard. The plate and bore are almost equal in size and if not stopped by the set screw, can jam. A fully closed throttle plate would never kill the engine as long as the idle stepper motor ports the required air as needed through its own port. So, for the idle valve to manage the 800RPM as required, the throttle plate must be at its almost closed position, but not too closed as to jam it, hence the reason for the set screw stop it. If it is open too much, then any additional gap dimension will add RPM to the 800 and raise it by that much.
I apologize for not following up on this one.

 

Thanks bigtime Carsnplanes. I'm going to remove and clean my throttle body and I might have found that set screw, but now I know. My car would stall out when the throttle closed all the way and I had a temporary fix by adjusting the slack in the throttle cable. Maybe my stepper motor is bad or there could be an electrical problem. I will be cleaning and checking it all. Thanks again.

 

Do not mess with that screw until you have crossed off all other issues. What Carsnplanes had is not common, and if you mess with that screw, it could cause you to chase your tail.

Cleaning the throttle body is usually the cure for your problem. For some reason, once cleaned, the TPS needs to be reset sometimes. It can be done by hand, but you can either search the forums or come back here to learn how to do that IF it needs to be done. If you want a jump start, loosen the screws holding the TPS in place just a little bit. If your car starts up and idles like it should, just tighten the screws (bolts) in place. If not, you will be able to make incremental adjustments to the base idle (when hot please) and then tighten it down.

BTW, when you're removing the throttle, make sure to have some golf tees on hand. There's a coolant hose that needs to be disconnected. Golf tees fit perfectly to block the line up while disconnected.