Hello fellow XJSers!

Apologies for the wall of text, I want to make sure I explained my situation as best as possible in the most concise way.

So I took Morris out of storage seeing that winter is about out and Fall is slowly coming in. Along with dusting off the old cat came time to do emissions and renew tags here in Colorado, USA. Lo and behold, it failed emissions in spectacular fashion, as it is apparently burning gas (high HCLs) FOUR times of what's allowed (max is 20, I was getting 80's). Yikes! The main problem appears to be that the engine is not getting hot enough for the computer to start using Oxygen sensor information and adjusting the fuel:air ratio. The temp usually stays between the bottom and the "N", sometimes higher, often lower.

Some history of the work I've done on Morris in order over the past two years: Changed both thermostats when I first got her (they were stuck shut), then had the water pump rebuilt, next the radiator re-cored, had the timing professionally checked and corrected (I messed it up when I changed the pick-up coil), and just changed the thermostats again.

Morris will NOT GET HOT! I used to be able to cook bacon on the hood when I first got her, now I can literally touch the hood after it's been running hard and it's mildly hot. I used an infrared temperature sensor on the water outlets, and both read between 140 and 150 after an hour or more of driving (with the new thermostats I just put in). At best, the temp will sometimes go to the bottom of the N when driving hard and idling, but then it dives back down between zero and "N" (and I mean it goes down fast).

What gives? This engine is supposed to run hot, and here I have the exact opposite problem where I can't get it hot enough. It's been around 60 degrees here in Colorado, so I can't say the weather has to do with it. Radiator fluid topped off and burped accordingly, all fluid levels are good, all spark-plugs are firing (according to mechanic). So I am currently at loss as to what to look at next.

Any ideas? :\

 

Assuming that the engine is running on all 12 cylinders I can only think of a few reasons that it would be running cool;

1. Thermostat stuck open
2. Water Temperature Switch stuck closed and making the electric fan to run full time.

I know you said that you replaced the thermostats but its possible you got a bad one. Its the first place I would look.

Mark

 

It doesn't matter if the fan is on all the time. You could have dual fans on all the time and the temperature would still be regulated by the stats.

What stats did you put in it? It has to be a very specific stat. The way the bypass system is setup means they have to be a specific length for it to work. It sounds like they are either stuck open or not the correct length

 

Are the stats available there with different temperature ratings ?

Maybe you've been sold some stats that open earlier than Jaguar spec. They should have the temp etched into them. 88oC I think is the right one ?

 

Something to try...

1. Download the V12 Engine Performance Guide (that's probably not it's correct name, but someone will chime in with that). It has a chart of engine coolant temperature vs. sensor resistance.

2. Unplug the cable from the coolant temperature sensor. Jumper a resistor across it (car won't start without seeing a resistance value across those wires). I can't download the chart at the moment, but pick a resistor that's is close to what the chart says is about right for your ambient temperature.

3. Start it up, let it idle for 10 or so minutes. Then measure the resistance across the sensor. If the sensor is good, it should give you a resistance that is close to the corresponding value of what your thermometer is showing the coolant temperature at the outlet is. If the values are way off then maybe the CTS is bad???

If the values are close, and the coolant really is "cold", then thermostats seem to be the next thing to examine.

The above idea may seem somewhat convoluted, but it doesn't involve draining any coolant, which always seems to make a mess (especially if you have the stock coolant drain).

As I said, just something to try...

John
1987 XJ-S V12

 

Update! I think I found the issue.

First, thank you for your replies. V12s have two thermostats. So your ideas made me think: hard to believe that two new thermostats that met OEM standards would go bad right after installing, especially as I've used this brand before and they worked pretty well.

This wasn't the problem, though. I sat and thought and pondered about what might have changed since it ran well. Aside from the timing being off a bit and now being fixed, the car had sat FOR FOUR MONTHS.

That turned out to be the clue to the culprit, that the car had sat. What in the car would go bad after a while? Ah, gas. Gas goes bad after a while. I ran Morris until I used up most of the old fuel, put in new fuel, and temps are now back to normal. It also explains why I was not burning gas properly, and why more gas was being unburned after the timing got put right.

So the lesson here is to use gas stabilizer. Or not leave sitting with a full gas tank.

Thank you for your replies, they helped set me towards the solution!

 

With fresh fuel and proper temperatures I'm curious to hear if it now passes emissions. Please let us know how it goes.

Mark

 

Well drat! Or hogbiscuits! Whatever the British use.

Morris failed smog test again. This time with 3x over allowance on unburned fuel. And it's struggling to get to normal operating temp AGAIN. It was 60 degrees outside, left the air conditioning running, and I drove her for a while before taking her in.

New thermos rated at 190 both sides. Spark to all the wires. Timing has been checked and rechecked (26 before at 3000 rpm with vacuum closed). Argh, Morris girl, what could it be?

Am going to take our spark plugs. Maybe it will she'd a clue as to where the problem may lay.

 

What happens if you just let it idle for 20 minutes or so (and I mean don't drive it at all, just start it and let it idle)...is it still "cold" as measured by your IR thermometer at the coolant outlets?

So this issue started after replacing the thermostats?

Thanks,

John
1987 XJ-S V12

 

I'm re-opening this thread because I came back to the old girl hoping to get her to pass smog.


Last time I was here, I had replaced both thermostats, and it would remain cold (barely getting to the "N"). I FINALLY got the oxygen sensors replaced, both sides, and took her for a 20 mile drive, hoping that these would help get the temperature more normal by giving the correct air-fuel ratio.


Alas, I hate to report that Morris is apparently running even MORE rich, as over the course of a 20 mile drive the gas tank went from 3/4 full to 1/2 full, and it barely managed to get just over half-way to the "N" in temperature. So, it's running even worse.


Summary on what I've done/checked:
1. changed both thermostats twice (I have four just sitting here, two new ones in her)
2. fuel injector all firing properly ("click-click-click")
3. new oxygen sensors on both sides
4. all spark plugs are firing properly


I'm running out of ideas and scratching my head. Is it possible there's a broken or plugged up hose somewhere I don't know about that is related to fuel-air mixture? Someone said to "check the air flow sensor", but I have no idea where it is.


Help, I'm getting tired of using my 4x4 Suburban and want to run wild and free in Morris!

 

Maybe I can help. Check your PM's.

Mark

 

Hi

This doesn't sound anything like a problem with the Thermostats but much more likely to be a faulty Coolant Temperature Sensor (see Pic)

The Coolant Temperature Sensor, sends a message to the ECU in order to tell it how much fuel to deliver.

In the event it is faulty, then it could make the engine run 'Rich' and as such could be the reason, why your Car is failing the 'Smog Test'

The First thing to do is Check the Plug, as they get Corroded and could interfere with the Signal being sent to the ECU so give that a Clean or maybe get a new Plug. (Don't lose the spring clip that holds it in place)

Also Clean the Terminals on the Coolant Temperature Sensor.

That could well be all you need to do, unless you want to go 'belt and braces' and treat yourself to a new one, as they don't cost megabucks.

NEW BMW E23 E24 Jaguar XJS Porsche 928 FAE Engine Temperature Sensor DBC3728 | eBay

 

Now the temperature switches would make sense. Using an infrared thermometer, the car is running about 140 degrees (give or take about 5 degrees), and if the ECU is being told a different/colder/no temp, then it would try running the fuel mixture richer than it needs to be.




It is my understanding that the V12 has two temperature sensors. The left/US driver side is for the temp gauge in the dashboard, and the right/US passenger is for the electric fan. My electric fan is turning on, although now as I'm thinking about it, why the heck is it turning on when the engine doesn't even reach normal operating speed? Does the ECU increase fuel when it is signaled that the motor is warm? I would think it would decrease fuel, but I'm not sure of much at this point.


I'll check and clean the leads to both temperature sensors when I get home tonight. I'll also see where I can obtain them if the leads look clean, as these are probably the originals from 1989. If any of you know, which of the two sends the signal to the ECU? I'm guessing the left/US driver one by the last response.

 

If the Coolant Temperature Sensor is faulty and needs replacing, it might not be sending any Signal at all and as such won't be reducing the fuel supply when the engine gets hot.

It should be by the Oil fill Cap next to that curved hose as in the Pic.

 

I agree with you, if the engine temp switch isn't sending a signal to the ECU that the coolant is hot, it won't adjust the air-gas ratio. The only thing here is that the temperature gauge on the dash is giving readings that are comparable to those I get when using an infrared thermometer, leading me to think that the temp sensor is working correctly.


Still, I'll clean the leads, as they are probably due to be cleaned by now. Maybe I'll accidentally knock out the bugger with whatever is going on.

 

I believe the temperature sensor for the gauge is different to the temperature sensor used by fuel injection ecu

 

Put a few bottles of injector cleaner through it. We used to get high emission read outs due to blocked injectors. Although they were firing the spray pattern was off causing unburnt fuel in the exhaust. We used Redex at the time but see what others recommend.

Or you could have the injectors removed and cleaned.

 

Sounds good advice

 

A thought out of the box: While you are in the engine compartment. Pull the vacuum line from the fuel pressure regulator. Make sure it is not wet with fuel. A rich running engine also runs cooler.
Could be chasing the feathers instead of the chicken.

 

Have you measured the temperature difference across the thermostat housings with your IR thermometer? As it's warming up it should be hotter on the engine side than the outlet side of the thermostat, at least until the thermostats open. It should be very noticeable when the thermostats open.

If the temp stays the same on both sides, it means that the foot on the thermostat isn't sealing off the bypass passage and the coolant is going around the thermostats.

If the engine truly isn't coming up to temperature, then changing the sensors won't make any difference if they are in fact reporting a true temperature (as seems to be the case here).

Thinking out loud, can you get a set of pinch off pliers? There are ones designed for pinching brake hoses so you don't lose fluid when the system is opened. As a thought, try pinching off both upper rad hoses and start it. That will force the coolant to not circulate through the radiator and see if it warms up to the proper temperature.

A further test would be to see if you can feel the radiator as the car is warming up. Until the thermostats open the rad should stay cold. If it warms up along with the engine, then you know the coolant is not being held back in the block by the thermostats.

I would not look any further until proper operation of the thermostats can be verified.