Hi all, been lurking for a bit and got some great information off this Forum but I'm starting to run out of ideas. I bought my car, a1990 XJS V12 about a month ago, and have been elbow deep in it since. I initially had a no-start, which has been rectified by replacing the cap, rotor, amps, coils, plugs, wires, etc... Everything I've replaced has resulted in an improvement.

I'm haunted by two issues:

One, the gauge on the dash overheats after about 10 minutes of idling at about 700rpm. It will climb pretty far up above the N. I've replaced this sensor. The mechanical fan seems to be working correctly. It picks up right away, and stops immediately when I kill the engine. I have never seen the electric fan come on, even when the gauge says I'm well above the N. The coolant hoses seem warm, but not hot. The radiator honestly stays cold. Like I can touch it even when supposedly the engine is overheating. Is this possibly a bad water pump? Is it an issue with air in the system?

Two, I have more pressure on the left hand bank than the right. I think I detect a bit of a misfire from the left as well. Right side is a rhythmic put-put-put when I put a card over it, while the left is put-put-slap and way more exhaust coming out. Also seems warmer. The vehicle intermittently runs a little rich on either side, really seems to be dependent on temperature.

When I initially got it, I'm pretty sure it was on its way to a Marelli burn down. The rotor had a tiny bit of scorching. The cap also had a bit of melt. What actually killed it was that the crank/speed sensor wire down by the transmission melted through, as it was routed against the manifold. I extended and soldered this wire back together. The air filter on the left hand bank had a little scorching going on. Might have been from an ignition in the crank that travelled through the PCV?

Anyway, any insight is appreciated! I'll keep plugging away at it, but I'd really like to fix the cooling issue so that I can run it and diagnose the unbalanced exhaust.

P.S. Why is the oil pressure light on but the gauge responds very well to changes in RPM?

 

Also forgot to mention that I've replaced both thermostats.

 

There is a low coolant light illuminated on the gauge cluster. It could be that the coolant sensor is unplugged, or it could indicate that the coolant level is low.

When you replaced the thermostats, how did you bleed the system? Its kinda a pain to get all the air out.

Unfortunately the cooling system is one of those areas that's worth going through fully, top to bottom, rather than trying to chase individual problems. Replace all the hoses, thermostats, get the radiator recored or replaced, new water pump, et cetera. Then, with fresh coolant, it should be good for a bit.