Before I start- it's a 1989 xj40 sovereign, straight 6, 4.0L in hot humid tropical Queensland, Australia.

SO.. I am having quite a decent amount of moisture in my pipes, and white smoke on startup. now this would be a 'yeah condensation' issue if I were to live anywhere else I'm sure, but it's 26 degrees celcius and 65% humidity where I am right now- so it can't be condensation. It's been a small issue for a while according to my partner, who says he sees a little smoke when I accellerate out of corners sometimes, but today especially I've noticed a cloud of smoke upon startup which was much larger than usual. It disappeared after a second, but later in the day I started up and it was there again- though there was a drive between those two times which it didn't smoke at all on startup.
Tail pipes have moisture droplets in them, they're not green but for all I know my green coolant could be what's condensating and maybe it comes out as clear?

Now in any other car I'd be checking the coolant where the radiator cap is to see if there are any bubbles- but how the hell on my jag? I've got a coolant tank on the side of the engine bay (with the most vague idea of whether it's full or not ever due to no level marks), but there's no damn radiator cap- so how do I check this?
I have some coolant leaking from the cap area at times (about 1/4 of a teaspoon tricking out of the coolant tank lid, but the level hasn't really moved much since I got the car about 6 months ago now. it's a minor thing.
Oil is clean and not frothy.

I worry I have a serious issue coming up, what's your input?
ps- I have had pretty bad fuel mileage lately, not sure if that's connected.
Cheers guys x

 

Under the cap on the coolant reservoir would be the place to check for bubbles while running. Another test would be to pressurize the cooling system via the cap on the coolant reservoir to see if it holds pressure. If it doesn't, and there's no visible coolant leak, then that doesn't leave many other places for it to go, other than the combustion chambers.

Before I had done any work to my car, I borrowed a tester from my journeyman to check for combustion gases in the coolant reservoir. It's basically a tube with a rubber tip, you fill with a special fluid and place the tube in the hole where the reservoir cap was. If it detects combustion gases, it changes color.

Hope to help, cheers!

 

Hello, à little video to explain 👍

 

Hi Beck,

I'm tired so forgive the scattered reply:

I guess my first question is how certain you are that the moisture in your tailpipes is water and not petrol?

White or bluish smoke on startup is very common with XJ40s due to oil sliding past the worn exhaust valve stem seals into the cylinders. So your engine burns a little oil whenever it is running, but when the engine is off, oil that has pooled on top of the cylinder head drips down the valve stems, primarily on the exhaust side due to the tilt of engine. So when you start the engine there is an accumulation of oil in each cylinder, which burns off for several seconds or more when the engine is started.

Two common causes of poor fuel economy are a coolant thermostat that is stuck open, preventing the engine from reaching optimum operating temperature, or a coolant temperature sensor (CTS) that is stuck at a cold setting, prompting the ECM to continue applying cold-start fuel enrichment even when the engine is warm.

I have experienced XJ40 head gasket failure three times, once on our '88 and twice on our '93 about 90,000 miles apart. In all three cases, I had no warning until suddenly the car lost power and began belching clouds of white steam from the exhaust. Up to that point, I hadn't noticed any unusual lost of oil or coolant, any excessive smoke from the exhaust, or any decline in performance.

All that to say, I don't know what's going on with your car, but a combustion leak test like the one in the video posted by frenchfairplaydriver might give you some peace of mind (or confirm your worst fears).

Cheers,

Don

 

Thanks guys, I'm certain it's moisture as the smell is nearly sweet, there's no burning oil smell and the tailpipe walls fill with droplets of water immediately upon the large cloud. If I lived in a dry environment I'd be less worried and take it for normal condensation but we're up the 65-70% humidity at the moment. I feel if I have a gasket leak it's only a tiny crack so went ahead with a bottle of rislone (bars leak) head gasket fix last night so we'll see how she holds up today. Fingers crossed!

 

Hi Beck,

Jaguar used to recommend a bottle of Bars Leaks with every coolant change, but at some point they discontinued this recommendation, apparently due to the small passages in heater cores and elsewhere being clogged by the sediment in the product. I hope your experience is positive!

Cheers,

Don

 

...and blocked radiator passages as well.

How many kilometres are on the vehicle? What is the condition of the spark plugs?

Has anyone performed a pressure check of the cooling system, or compression test of the cylinders?

Without some basic tests being performed, any guesses as to what may be the cause of the water vapour is just speculation.

 

Absolutely, I'll be bringing her in to a jag shop in a few weeks but definitely didn't want to risk a whole blow in the meantime- so trusting IF there is a tiny crack in my gasket, this stuff should hopefully be a little line of defense. I'm going to get the shop to do the diagnostics for me and if we're facing a full gasket replacement I guess I best be selling what I can to pay for it hah! If it were any other car I'd sell but I plan to drive this cat daily until I keel over.

 

Hoping it's not your head gasket, but rest assured that the head gasket job is not too bad on an XJ40. It's been several years since I've done one, but at that time the parts weren't too expensive. But the job is time consuming so if you have to pay for labor that will add up.

Please keep us informed!

Don

 

Hi Beck, the test in the video is called a TK check (test) any good garage should have the equipment. If you have one near you it shoudn’t cost too much for them to carry it out. That way you can determine yay or nay on the head gasket.

 

Hi Beck,

I don't know about terminology Down Under, but in the U.S. the test Robman25 is describing is also known by other names, including Combustion Leak Test, Block Test, Head Gasket Test, Compression Fume Test, etc. This test can detect combustion gasses in the engine coolant.

There are some tests you can conduct yourself, such as checking the oil fill cap for an accumulation of goo that looks like mayonnaise, but this test is not always conclusive on XJ40s because they tend to have moisture and condensation in the crankcase and breathing system much of the time.

You can also remove the spark plugs and inspect them for signs of wet coolant. Look down into the cylinders for signs of coolant, and if none is visible, remove the fuel pump relay and crank the engine and watch for coolant spitting out of any of the spark plug holes.

I'm sure the Internet has lots of other tips for diagnosing head gasket problems.

Please keep us informed.

Cheers,

Don