Weird Disco Overheating after Head Gasket Job

[Tom Jones]

My son bought a '97 Discovery with blown head gaskets. We pulled the heads, installed new OEM head gaskets and intakes, reassembled. Heads were decked, new head bolts properly torqued. Car was assembled with coolant and copper Bar's Leak to stop any pinhole leaks.

Once assembled, car started first try. It ran 20 minutes with just a small amount of steam, but no water seemed to be lost in radiator. After that, it stopped steaming, ran just fine. He drove it about two miles, then suddenly the engine speed increased and then it overheated and blew out about a third of the coolant. We allowed it to cool overnight, refilled the coolant and let it burp. Ran fine at idle, then suddenly, the engine speed increased and coolant again burped out.

If the engine is revved up it runs pretty good, then kinda makes some loud bangs - either in the exhaust or perhaps its a loud knock.

My thought is that the engine is either suddenly going very lean or that timing is somehow advancing. Or maybe we missed something, or its just a bad omen of things to come. Maybe its just full of crud - the prior owner apparently ran it without therostat and with only water for a long time. There is LOTS of deferred maintenance on this car.

Oh - and it shimmy's in the front end! 'Natch!

Any thoughts?

How is the fuel/air mixture actually controlled in the fuel injection?

And where is the sensor that triggers the spark? Maybe it's loose?

Thanks!

Tom

[p76rangie]

How did you know it was a head gasket?
Did you check for slipped liners while you had the heads off?

[pavel]

There could be any number of reasons for your engine troubles. The first thing that comes to mind is that your cooling system is plugged up or full of air. Most "stop leak" formulas I've come across warn not to use if the rad is suspect. If your radiator is partially plugged, the 'Bar's Leak' will finish the job, so to speak.
Aluminum engines don't like overheating, so it is possible you've done additional damage to the heads/block faces... let's hope you are lucky.

Make sure the coolant is flowing and the rad isn't plugged - do a major flush and see if that helps. No wait, take the rad out for pressure flow checking. Also call up the dealer and speak to a mechanic. Describe the engine sudden RPM increase and boiling. They might give you some hints over the phone...

You need lots of opinions on this problem, the "shimmy" is more straight forward to fix.

Cheers

Pavel

[Tom Jones]

I knew the head gasket was blown because when the engine was running, hot exhaust gasses blew out of the back seam between head and block on the left side. When we pulled the heads, that gasket was blown.

The liners were all in place, tight to the deck. Before reassembly we checked the block deck for straightness with machinist. Maximum deviation from straight was less than .001 on block. Heads had .002 warp, were trued up on mill.

There were no visible cracks in any cylinder.

I think what I find most likely is that the block and radiator are both clogged up - a lot - even though we did a very through flush.

What was weird, though, was how the engine would idle for 20-40 minutes, and would drive for a while, but the idle would surge up and soon the engine overheat. It seems that the mixture either went very lean, or the timing went way advanced.

I might note that the first time we started it it started first spin. Other times it would take a lot of cranking with that little effortless bump that comes when the timing is advanced.

We are pulling the radiator for flushing, and will try a more aggressive block flush.

Any thoughts on the idle/timing-like issues?

Tom