Hey,
Starting from the beginning:
I've been running water in my xjr6 all summer because it has a coolant leak from the water rail, and didn't have time or space to tear apart the intake to fix the leak with new gaskets and hose. The water stayed pretty clear all summer. I don't remember the exact sequence of events, but at one point I pulled out of a parking lot somewhat aggressively and the return hose at the top of the radiator after the thermostat popped off. I didn't notice because my low coolant sensor is broken, and didn't realize something was amiss until it wouldn't rev past 2k under load. I stopped pretty quickly after that, found the hose had popped off, put it back on, and filled it with water from a friendly homeowner . As far as i know it never overheated, never saw the temp gauge go above normal, etc. Not sure when it happened, but I think afterwards, the water started getting brown and gunky at the coolant cap. Also, when I remove the cap after running, I hear a hissing noise like gas is escaping (or entering). I haven't been able to figure out if it's positive or negative pressure, but the coolant reservoir smells a lot like exhaust fumes. I got a block tester kit and used that, and it showed up negative, but I'm not sure if I did it wrong or it only happens under certain conditions. The coolant was/is brown and frothy, the froth is only when hot.

The strange thing is my car still doesn't overheat, this is monitoring both with the temp gauge and with my obd2 reader. Since this incident/over time since I've owned it, the car went from zero leaks to leaking a bit of oil, such that I can tell where I've been parking often etc. The oil leak seems to be worst at the front of the valve cover, but it's hard to tell with all the hoses. Also, the oil pressure according to the gauge is a bit lower than normal. I still have to top coolant, and the car is now very very slow to heat up, like over 20 minutes of highway driving. To the point that it will not get up to normal operating temperature unless I drove more than 55 mph. (According to the gauge.)

I've finally got around to tearing the intake apart to get at this stupidly inaccessible hose and gaskets, but I'm wondering if while I'm at it I should replace the headgasket as a precaution.

My questions are:
What could be the source of all this rust/brown in the water? I pulled the water pump and it looks fine, and my understanding is the radiator is aluminum, as are most of the cooling system components? I know the reservoir smells like exhaust fumes to me but I'm not sure if I should trust my nose or the block tester kit.

Why the slow heating up? I pulled the thermostat and it looks fine and doesn't seem to be stuck or anything. I have a new one coming tomorrow just in case.

What are the odds of this being a headgasket? If not a headgasket, what could explain the pressure in the cooling system even days after driving? Cooling and contraction of the gas in the reservoir? Nothing to worry about?

Thanks for any help!

 

In my opinion , as to weither you replace the head gasket or not as a precaution dewpends if you value the ngeine as a whole .

It is already sespect .

But then warpage of the head is also suspect regardless of not seeing the temp spike with the indication system on the X300 . Lacking .

If the coolent mixes with the oil it will be compromised ruining the main bearings and such to the point of seizing the engine .

I have seen this before on a GM as a coolent coolerd slime climbing up the dipdtick , in that case it was too late , ruined engine .

 

Thanks for the reply,
There was no oil in the water when I drained the radiator, and no water in the oil/dipstick looks perfect and oil is an even, golden brown. This is why I'm somewhat perplexed, as I don't seem to have any of the classic symptoms of headgasket failure... No white smoke either.
I want to trust the block test but I also am not opposed to doing the head gasket, other than the cost and taking my car off the road for awhile. Are there any other tests I can do to verify a warped block or a blown/corroded gasket without removing the head?

If the head is warped hopefully it's within machining tolerances! If not, are the regular xj6 heads a direct fit?

 

If you're only running water instead of a water/coolant mix, the brown color in the water is rust. Coolant has rust inhibitors.

Water itself is actually a more effective coolant than antifreeze/coolant as far as heat exchange goes. But water causes rust and doesn't have the temperature abilities of antifreeze/coolant, of course.

The thermostat has probably gone bad, a slow warm-up is the usual symptom. So definitely install a new one. While you are below the manifold, be SURE to replace the two gaskets on the water rail: EAC9745. They are known leak points.

Run another block test if there is any doubt. A head gasket job is a big one and typically, the AJ16 head gasket is pretty sturdy.

Oil tends to leak from around the timing cover and/or the front corner of the head gasket, but again this is typically not a serious problem.

 

Thanks!
I'm going to keep the headgasket on and hope for the best.
I'll just move forward with the water rail gasket, water rail hose, thermostat, and thermostat replacement procedure. I removed the whole thermostat housing from the car, and in the process disconnected the bypass hose from the housing. I noticed per the parts fiche and the cooling system description that this is part of the lower radiator hose, or, the so called "octopus hose." I also have a valve cover gasket set (minus the bolt O-rings) that I'll probably install afterwards, see if it fixes/helps the oil leakage, but that will probably be a couple weeks from now given my slow progress.

I originally sprung this leak because I had removed to the water rail to clean the throttle body (stalling issues), did not replace the hose with a new hose, and replaced the original water rail gaskets with water gasket paper copies that I made, and these and/or the old hose were leaky. Considering this experience, I'm thinking about replacing the lower hose, simply because I disconnected it and I'm a bit worried about it leaking when I put it back together. Is this a valid fear, and should I spend the money + time to replace the octopus hose while I'm at it? I'm assuming yes but I wanted to get a second opinion. Obviously I've learned from that experience that I can't cut corners on this thing...

If I do replace the lower radiator hose, it seems I'll need to remove the supercharger to do so?

I tried to remove the supercharger once before but couldn't seem to get good access to the bolts under it. (With this car, all the nuts and bolts are SO inaccessible). Looking at it, I was thinking of moving the hard mounted hoses that go nearby it on the fender for better access, but any other tips would be much appreciated.