So this is new and sudden in my 1987 xj6. After running fine for months, There is a little whiff of smoke in the engine bay from under and around what i think is the exhaust manifold and it was very low on coolant there is also smoke coming out the rear pipes and it runs very rough.

Any general ideas? My instinct is to start pulling things off until i find a leaking something, but i wouldnt know where to start. Thank you.






It looks like it.might be from around this sensor, but could be dripping deeper in too

 

Low on coolant.... I'd start with a cooling system pressure tester. You fill the system and use it to pressurize the cooling system up to 14lbs or there abouts, wait a few hours, maintain the pressure and see where the fluid goes. Good luck!

Radiator Pressure Tester Kit

 

Cooling system pressure test, along with a compression test of the engine, as well as a visual inspection of everything in the engine bay.

 

Possibly a leaky cam cover gasket dribbling a bit of oil on the exhaust manifold....which might defy casual observation due to the manifold heat shield.



Black smoke? This would suggest over fueling.

Or more like a white vapor? This would suggest a blown head gasket.



Possibly related to the smoke...or as innocent as an old fashioned ignition misfire due to old spark plug, worn distributor cap, or the like




I agree with previous suggestions

Did the smoke and rough running appear suddenly and simultaneously?

Cheers
DD

 

Start with smoke ID!


1. White = water vapor.
2. Blue = oil
3. Black = excess gas.


Examine the spark plugs for clues.


1. One or more a lot cleaner. Steam cleaned by water from the cooling system into the combustion chamber.
2. Sooty black. X's fuel/
3. Oily black. Oil in the combustion chambers.


General;


Wet and dry compression test. Engine health or lack thereof.
Vacum guage. Steady as she goes or erratic. Leaks!!


Carl

 

The smoke and rough running appeared simultaneously. I went in took out the spark plugs and they all look to have the same amount of wear and tear, nothing dramatically different to my eye. The photo is of the plugs in order from the firewall to the front of the engine left to right. The coolant is still full. Thank you for all the help I love this car and it's fun to learn more about it. You guys are an invaluable resource

 

Spark plugs look decent.


The sensor in your picture is an O2 sensor. It senses combustion products as to rich or lean or normal. It can induce minor corrections only. It should be tightly screwed into the manifold. If not, exhaust gas and a bit of noise can leak. Look carefully with engine on for whiffs. Do not disturb unless absolutely necessary. Easily messed up and expensive.


When my car was a DOHC it's sensor was quite loose. No harm that I noted.


I'm with Doug and suspect weeping of oil on to the super hot exhaust.


Carl

 

replaced the spark plugs, distributor cap, and rotor, and it revs much faster now when pressing down on the gas, but no other real change. However, after a 7 mile test drive, the coolant light went on when accelerating in the city around 2000 rpms briefly. Got home and the coolant tank is empty. That's not good.

 

Well, not as bad as you think at least on two levels.


1. The light functioned correctly. Way back in 2001, mine did not.
dire consequences.


2. It might well be an external leak. The brown plastic tank it self.
Not unknown for them to spring leaks. The cars have a lot of rubber hoses. Often, merely tightening the clamps fixes a weep. The filler cap might be offing early.


Fill it. drive it to temperature. Park, pop the bonnet and examine
all parts of the system carefully.


Yup, a healthy ignition system makes all critters purr....


Carl

 

When the engine is cold, is there any residual pressure in the coolant jacket. If you release the pressure cap and get a great big "whoosh" then head gasket failure is likely. The fact your symptoms are so sudden points to that.


Although the later slotted blocks on the engine eliminated cracking between the bores, the engines don't normally hold a head gasket beyond about 80 - 90k miles. Over that and you're on borrowed time !

 

Thank you. There is no pressure in the system when done driving, so I'll look for that leak next weekend and hope if worse comes to worse it's a gasket not a crack. Not sure i can tackle either myself, but i know a nice garage guy

 

So I took off the heat shield to get a better view of what was going on and there is a very large crack in the rear exhaust manifold that I'm pretty sure was leading to the smoke I saw. I will pick up some high heat weld and fix that.

I also tightened all hoses and filled up the coolant. It stayed full for a short dtive to warm up the car. I may chalk that one up in the fixed column if it only loses a little bit of coolant over the week.



Looks like a previous repair

 

Found!!! Eureka, a large step forward.


But, a tough fix. Cast iron welds poorly. It can be
done by an expert with the equipment. In situ,
doubtful.


Seek a healthy used replacement. And that is fraught
with peril. Corroded fasteners busting....


There is a way to "stitch" cracks in cast iron.
Drill and tap over lapping holes/ Install fasteners,.
bust or grind off the heads. Repeat, over and over.


Or:


Live with it. It is harmless" !!!


Carl

 

So i tried a jb weld type material good to 2700 degrees. I don't expect it to last forever but for $8 (and silent purring) it's worth redoing it every couple months if it pops off. Eventually I assume I'll have to replace all the gaskets and I'll deal with the manifold on a more permanent basis at that time. I would love it if the engine compartment were a lot cleaner than it was right now

 

Got a full engine bay photo?

As for tidying the bay up.

Source another set of manifolds for a future change, and prep and paint them in some high temp paint, plug the EGR while you've got them off.

Remove the EGR pipe into the rear of the inlet manifold, make a block off plate to replace it.

Eliminate the Air injection setup, 1/8th BSP plugs in the head plug the holes from the removed air injection pipes, and you can just completely unbolt the air pump, also one less belt driven pump

 

I have a nice crack in mine, too. Some day I'm going to borrow one of those cameras on a stick and see if it really goes all the way through--maybe it's just a surface crack.

 

Short drive to warm up the car, and all the coolant is again gone, with almost zero pressure in the system. Now, however, after I shut off the car, I can literally hear coolant dripping and evaporating off something hot, but I can't see it. The drips are about every 2-3 seconds, and I see no smoke and nothing on the ground. It sounds like it might be louder on the passenger side, and it is definitely nearer the firewall than the front of the engine. When I removed the expansion tank cap, the dripping stopped. (No whoosh at all from the cap, but I suspect at least a little pressure still in the system to force the drip.)

I'm stymied, but I will crawl around under the car and poke my head further in the engine bay and feel around when it's cool to see if there's anything else to tighten.

Any idea what it could be? If anybody's asking, I really want to hear loose hose, not gasket leaking. I will add that the inside air vents were sticky and dust covered when I bought the car, and I've always wondered if something in the heater core is messed up.

By the way, I seriously love this car.

 

Maybe a core plug. These are steel and can rust out. If the coolant is disappearing after a short drive it must be absolutely gushing out and should be easy to locate the leak. However, core plugs are along the two sides of the block and can be obscured by the inlet and exhaust manifolds.

 

I will get under the engine tomorrow and check that out, too. It was sort of my assumption that a fairly fast drip with only residual pressure means a pretty good-size leak under engine operating pressure, so I hope I can find it. Well, and then be able to fix it without removing 500 different things.

 

You can get a cooling system pressure kit from your local parts store (rent for free - AutoZone and O'Reillys have them) and pressure your cooling system while things are cool and are under the car. You will have a much better chance determining where the leak is.