I have a Jaguar X300 4.0 on a 1997 plate. I had a problem with fuel consumption so I changed to air flow meter which did not improve the fuel consumption problem. I then took it to a garage and they put it on a diagnostics computer it showed problem with EGR valve. Which I have not changed as yet. The problem is when your driving and you stop you can smell petrol also you can smell petrol in the car and boot when It is left parked for a while. I cannot see any obvious petrol leaks underneath and have looked it over while on a ramp in the garage. It is returning about 12 mpg which it displays on the onboard computer. Also the engine temperature is showing as running really cold all the time. I know the weather is cold at the moment but the engine temperature barely moves even when waiting in traffic. Before when the weather was hot it would sit in the middle on the engine temperature display but not in the cold weather. Is there anyway to tell if the thermostat is opening and closing without checking it by removing it ?. Any advice would be great as I want to know what to do next someone said change the exhaust gas sensors and someone said change the thermostat as it may be stuck open all the time. Im stuck on what to do to fix the problem and do not really want to spend money on anything that would be a complete waste of time. It came up with the following error codoes for the egr:- EGR valve drive circuit malfunction and EGR position circuit out of range (low or high voltage).

Many Thanks Mat,

 

I would start by replacing the thermostat. Failing in the open position is a common problem with the X300. Your engine is running in open loop and the ECU is controlling the injectors in rich startup mode.

I'm not sure what to do with the EGR valve, but I do recall removing mine and cleaning the carbon buildup out.

 

Mat,
The thermostat would definitely be the best, and easiest place to start, and should definitely improve your fuel consumption.
If I recall correctly, EGR was only fitted to North American vehicles, and so shouldn't be troubling yours.
It is also worth checking the fuel lines, supply and return, for tiny leaks. A known weak spot on these cars, and nothing smells quite as like petrol as petrol!

 

Is it a easy job to do changing a thermostat yourself and do you need to order a new gasket also ?. Does anyone know If a stuck open thermostat would cause such bad fuel economy and the smell of petrol ?.

 

A replacement thermostat should come with the o ring. If you can't change it yourself you are probably going to spend a lot of money on future repairs. You can buy a copy of the repair manual online from Jaguar Heritage, as I recall. Someone from your side of the pond will likely chime in to assist.

As I mentioned in my first post, the engine is running in startup (rich) mode so that will probably solve the problem. Whether or not it cures the fuel odor I don't know, but I'm not going to guess about possibilities until the known first problem is eliminated.

 

Thanks I'm going to buy a replacement thermostat and give that a try. It looks easy to change to be honest. May sound like a silly question I know you need to put a new seal on the thermostat when you put a new one but is there any special paste you need to use to make a seal between the metal before you put it all back together ?.

 

Just make sure if yours doesn't have an O-ring, DON'T use an O-ring when you put it back together, even if your new thermostat comes with one. You'll break an ear off the housing.

If you don't have an O-ring version, a smear of RTV will work just fine when rejoining the parts, if you don't have a gasket.

 

Thanks for everyone's advice. Can you please tell me what the full name is for RTV or a ebay link then I will order it ?. I done a search for it on google and could not find it.

 

Silicone gasket maker, I think the big names are Permatex and .....hang on...it'll eventually pop in mind....

Edit: Loctite! and J.B. Weld, though they (JBW) are perhaps more famous for their epoxy, so don't get confused. I'd use the Permatex Ultra Black for the T-stat.....largely because I know I have a couple of tubes hanging on the pegboard out in the shop....The key point is, if your housing has a groove for the o-ring, use an o-ring, but if not, don't let an o-ring anywhere NEAR it!

 

Mat,
it is an easy job to change the thermostat, but I would advise getting the correct gasket/ o ring for your car, as it makes for a better and easier job. Check on the jaguar classic parts site for your vehicle VIN number, and it will show you the parts required.
If the thermostat is stuck open (which is the usual fail mode on these cars), the engine does not come up to temperature fully, which leaves the ECU supplying extra fuel for cold running, which will definitely affect your fuel consumption, and may in extreme circumstances cause a strong petrol smell, although I am less convinced on the latter point in your case.

 

I changed my thermostat today and I made a right mess of it. The paste was all over the place and I found it hard to apply the paste to the gasket as it kept getting stuck to my fingers. I put the thermostat in and bolted the thermostat elbow on and it was dripping slightly. So I drove it for a while the temperature went up and it was sitting just under half way. So I drove home and I took it all apart to check it and the thermostat elbow bolt hole snapped off. So I have ordered a new one and also a new gasket. I tested the new thermostat in boiling water and it opened as it should. I also tested the old thermostat which opened in boiling water also. It was not stuck open either. So I am confused why after fitting the new thermostat the temperature went up to nearly half way as it should. But with the old one it never even though it seemed fine when tested!. I also need some suggestions on the best way to put the paste and thermostat housing back on the car. I don't want to make a mess of it again. I thought this time I will put paste on one side of the gasket then put that on the thermostat housing leave that to set for 15 minutes like it suggests then put paste on the other side of the gasket then put it all back together. It says do not bolt it back together for at least fifteen mins after putting the paste on. But I was thinking how can I possibly hold it for that long. Also do I have to torque tighten the bolts as I do not have torque tools ?. I done them as tight as I could.

Any suggestion would be really appreciated.
Many Thanks
Mat

 

When I have a gasket that needs sealer on both sides I lay it on old fashion waxed paper, but a poly sandwich bag will probably work also.

You are undoubtedly over tightening the bolts. Never as tight as you could on bolts that small.

The old thermostat may have been stuck partially open and then freed up when you took it apart. Does it close tight now?

 

The old thermostat did close completely but I'm still confused by the whole thing. Because after fitting the new one and driving locally the car temperature stayed just below half and the temperature gauge increased quickly also. Which seems to suggest that the new thermostat was working better than the old one. Also there was no petrol smell as there was before. Do you think over tightening the bolts caused the thermostat elbow to break ?.

 

Do you suggest just tightening the bolts till the spanner stops turning anymore without applying any more pressure to tighten the bolts ?. Would that be tight enough to stop any leaks also ?.

 

Also any suggestions on how I will drain all the coolant from the car ?. I got told I cannot mix different anti freeze types. The one I brought was pink and the old one is blue.

 

Will I need to bleed the coolant system after putting water in the car ?.

 

If you are really using a proper spanner, I would suggest putting your thumb over the bolt head and grasping the spanner up near the bolt. If a ratchet, then grasp it by the round, ratcheting part, not out at the end of the handle. Alternate tightening between both bolts and when you feel things "seat" "hit bottom" what have you, just make sure it is snug - what torque you can muster while grasping the spanner near the bolt, not out at the handle, and without any grunting or passing of gas.

There is a draincock on the bottom of the radiator, I seem to recall it on left side, but the manual will show it. However, you will get not quite half the coolant that way. There is allegedly one or possibly two drain plugs on the block but I've never been able to find one. If you mean to change coolant types, you'll need to flush your system with distilled water. I recommend at least 12 gallons. Drain the radiator at the draincock (I've found it quicker and more efficient to just pull the lower rad hose from its nipple - but I may be thinking of the S-Types) You will get as much as maybe 2 gal out. Top up with distilled water, start the engine, and run it up to operating temperature with climate control set to full heat. Drain/top-up/repeat until you get clear water when you drain. Once you are satisfied that you've flushed all the old coolant based on good clear water draining, then you can top-up with your new coolant - make sure you use full-strength, not 50/50 pre-mix as your car will already be half-full of distilled water.


Matt, I'm afraid you have been a victim of too much advice: Since you got the proper gasket as CountyJag advised, you should have ignored my suggestion to use a smear of RTV and just fit it altogether with the dry gasket. I was speaking from what I *think* is the more common experience on X300, you order a thermostat, it comes in, with an O-ring in the box, you take your old one out, and there is no O-ring, but an old gasket that falls apart as you separate the pieces. In this case, scrape it off, both parts, put a bead of silicone sealer around the surface of one of the parts (where the gasket was) wait 15 mins, and bolt it back together.

As to the differing behavior between old and new - did you just toss the old one in a pot of boiling water and observe that it opened? Or did you put it in a pot of cold water and heat that until boiling? If so, did you also stir it with a thermometer and watch for it to start opening and note the temperature? When we say "stuck open" we may not quite mean that....we may mean Opens early - at too low of a temp.

 

Thanks for everyone's advice I really appreciate it. I put both thermostats in cold water I boiled the water and watched them open. Your also right as I thought maybe the old thermostat is opening to early. So I will fit the new thermostat and gasket I will not use any gasket paste I will just fit it dry and put it altogether if this is correct ?. I was also thinking not to put any paste round the thermostat before putting it in the car if this is correct also ?.

 

Right. Paste in lieu of gasket or vice-versa. Now...when you get over into cam-cover gasket renewal..the rules change, but let's not confuse things.

You have the proper thermostat housing gasket in-hand, so I wouldn't use any paste anywhere. And be careful tightening those bolts. Best to get a torque-wrench and do it to spec, but probably acceptable to grip the spanner up near the bolt rather than out at the end and proceed cautiously.
I can't recall exactly, but I believe the X300 T-stat has a sort of jiggly pintle that must be oriented at the 12 o'clock position? So beware of that, and again, memory is foggy, I may well be wrong on that point.

 

I received my thermostat housing and I removed just the elbow which I needed. The bolts where really tight and hard to undo. I tried putting my new thermostat in the thermostat housing but it would not sit in the recess it was slightly too big so I used the one that came in the thermostat housing. I put the new gasket on and used no paste and put it all back together. It was dripping ever so slightly but when I squeezed a hose it would drip a lot faster. So I took it all apart and used paste as well and put it back together again. It still leaked very slightly. So I took it all apart again and cleaned off all the old paste and I put new paste and more of it. I will put water in the car later today and hopefully no leaks. If it still leaks I will take it too a garage and get them to do it.