Clipped and simplified HTML, from http://mgaguru.com/mgtech/engine/de101a.htm.
DE-101 is a disertation on starting a long DORMANT ENGINE. It comes in two parts, the first of which is a short discussion on the possible sources of WATER IN THE OIL and a compression BLOW DOWN TEST.
Well, as this question was originally asked in reference to an entirely different type of car, I have reviewed it and changed a few names to protect the innocent, so now it is very generic and should apply to nearly any engine (at least piston engines), including our beloved MGs. The original inquiry also related to finding water in the oil, and because the answer has a lot to do with checking for a leaky head gasket it is included here as well.
A little water in the oil is common for an engine that has had the thermostat removed, or runs only short trips and does not get up to normal running temperature. This usually takes the form of a creamy emulsion on the inside of the valve cover, but can get bad enough to discolor the oil in the pan and on the dipstick as well. It doesn't necessarily indicate any damage to the engine, although a blown head gasket is also a common cause when there is a lot of water in the oil.
If you suspect a blown head gasket (or a crack in the cooling jacket wall) do a pressure test on the cooling system. I bought a radiator pressure tester at NAPA some years back for about $60, but any good service shop or any radiator shop should be able to do it for you. The device is a hand pump (looks like a short basketball pump), with a pressure gauge and a hose connecting to a fitting that goes on the radiator in place of the radiator cap. Fill the radiator with water completely to the top, leaving as little air space as possible. Attach the tester and pump up the pressure to about 10 psi. Then let it sit for a while and watch the gauge. If it holds the pressure you do not have a blown head gasket, at least not into the water jacket area.
The pressure may drop a couple of PSI to start with, and then stabilize. This can happen when the rubber hoses stretch a bit under pressure, but the reinforcing cords in the hoses should limit the expansion, and the pressure should stop dropping. Give it a few minutes and pump the pressure back up to 10 psi again.
If it will not hold the pressure, the water is leaking out somewhere. First place to check is the front of the water pump, just behind the belt pulley. Then check the water valve for the heater (if it has one) and all of the hose connections. If the water leaks out on the floor the source of the leak may be obvious. If it loses a substantial amount of water without making the floor wet, chances are that you will be finding it in the oil sump. The most common cause for this is a blown head gasket, but there is a remote chance that it could be a crack in the head or in a cylinder wall.
For an internal leak you can do a pressure test on each cylinder. You need a fitting that will screw into a spark plug hole and to which you can attach an air line, and you will need a pressure source, so an air compressor would be nice. You can make the fitting from an old spark plug, break off the ceramic, punch out the material in the center hole, and weld or braze an air fitting to the remaining steel part. For each cylinder in turn, rotate the engine to top dead center on the compression stroke for the cylinder being tested, apply about 20 psi pressure, and look for bubbles in the radiator. You might also listen for leakage into the crankcase, but any sound there may be masked by other (air leakage) noises. If you drain the oil and leave the drain plug out you might find water dribbling out the oil drain (not a good thing).
If you have gotten this far, congratulations, you would be smack in the middle of doing a blow down test on the cylinders, so listen up and check a few other things while you're at it. If you hear hissing at the carburetor you have a leaky inlet valve. If you hear hissing out the tail pipe you have a leaky exhaust valve. If you hear hissing at the oil filler cap you have leaky rings and blow by into the crankcase. If you have pressure on one cylinder and hear hissing at the adjacent spark plug hole, you may may have a blown head gasket between those two cylinders. This is fairly common between #2 and #3 where the two adjacent exhaust valves create a hot spot. With a bad inlet valve you can get a hiss between #1 and #2, or between #3 and #4, where two cylinders share a port in the intake manifold. With a bad exhaust valve you may get a hiss between #2 and #3 where there's a shared port in the exhaust manifold.
Another tool that should be in everyone's tool box is a compression tester (about $20 at your local cheap parts store). This is just a hand held pressure gauge and a pipe with a rubber bung on the end. You hold this tightly in the spark plug hole while you crank the engine over for several revolutions to allow the pressure to build up and the gauge reading to stabilize. You can then add a couple squirts of oil in the cylinder and repeat the pressure check. If the addition of oil to the cylinder increases pressure by about 20 psi, the piston rings are probably not sealing well. Ideally you would like all cylinders to have pressure readings within a range of 10% or 10 psi, but the absolute reading is not terribly important unless it's down around 100 psi or less. 130-140 psi in a good stock MG engine. 175 psi is a good high compression engine. Less than 100 psi makes it hard to start. Greater than 10 psi variation between cylinders gives it a rough idle.
And now on to the problem of starting a long dormant engine.
For a car that has been sitting for more than a year, the first order of business is to get rid of the stale fuel. It will most likely not run at all on fuel more than a few years old, not even a pop. Drain the fuel tank completely and put in at least two gallons of fresh fuel. This would be a good time to change the fuel filter if the car has one. Open the fuel line near the carburetor(s), and flush through until you get fresh fuel coming out. If the car has an electric fuel pump (and it works) this is a cinch. This is also a good time to check the electric pump to be sure it works. Otherwise you may use a hand vacuum pump to draw the fuel through the line. If the car has a mechanical fuel pump mounted on the engine, it would be a good idea to remove the pump and operate it by hand to verify that it actuall works. This could be another way of flushing the fuel line from the tank to the engine.
Depending on the type of carburetor(s), it could be convenient to remove the top of the float chamber and remove the stale fuel inside, and maybe clean the inside of the float chamber. Old evaproated fuel can leave behind an inert liquid similar to urine, or even something quite viscus like honey, or even a solid substance that looks like dried airplane glue. Wash this stuff out with a little gasoline, be sure the small hole exiting the float chamber towards the main fuel jet is clear, and be sure that the float valve is free to move by gravity alone. Reassemble the fuel system and fill it up with fuel. Verify that the lines and hoses will hold the fuel pressure without leaking, and _especially_ that the float valve stops the fuel flow when the float chamber is full.
If the stuff on the dipstick looks like anything other than reasonably clean engine oil, it would be a good idea to change the oil and filter before running the engine. When you're ready to turn the engine over, just remove all the spark plugs, give it a little cylinder oil and give it a crank.
It would be benificial to the engine bearings if you could prime the oil system before cranking it. You can NOT do it this way with an MG, but with some engines (V8's in particular) you can remove the distributor and spin the oil pump with a socket drive extention in an electric drill. With my MGA engine I remove the flex line from the engine to the oil pressure gauge and pump in a pint or two of oil with a finger pump oil can. I keep pumping until I can feel a noticable resistance to flow, meaning that I am then forcing the oil through the bearing journals. Any engine should have a port for an oil pressure gauge line or an oil pressure switch or transducer. Remove this fitting and use the port to inject oil into the engine before cranking it. Reinstall the fitting of course. This should (may) also effectively prime the oil pump.
To check to see if the engine is siezed, put the transmission in high gear (assuming stick shift) and rock the car fore and aft by hand. Backlash in the gear train will allow it to roll a few inches either way so you can put in a little inertia. Give it a good bump each way a few times and see it engine will rotate a bit. If it does turn, just get on the starter and crank it (without the spark plugs) to get the oil pressure up. The pressure should come up on the gauge (or idiot light go out) within a half minute or so, but it could take as much as a full minute of cranking the first time.
If the pressure doesn't come up while cranking, don't worry too much, it doesn't always work. Next step (if the pressure doesn't come up) is to prime the oil system again just for good measure, (shouldn't take much the second time around). Then put the spark plugs back in and try to start it normally. If it starts the oil pressure should come up within 10 seconds of running, otherwise you really have a problem. Don't run it more that 30 seconds without oil pressure. So long as there's an oil film in the bearings you're okay with idling, but with no oil pressure there's no oil flow, and the oil film will soon overheat and break down with damage to the bearings.
If the engine is siezed, the problem will most likely be that the pistons are tight in the cylinders. There are a couple of possibilities, but one could be that the rings are rusted to the cylinder wall in one or more cylinders. When an engine is stopped there is always at least one intake valve and one exhaust valve open, and these cylinders can breath with changes in temperature and barometric pressure. Over a long time some humid air can get in and allow rust in the cylinders. If the car was stored indoors with the spark plugs in place, there's a good chance that the engine is not siezed.
Another reason for an engine to be siezed is if someone put a little oil in each cylinder and then let it sit for years to dry out, especially if the spark plugs holes were left open. When the oil dries out it leaves a varnish deposit that looks a lot like dried tree sap or tan phenolic plastic without the fiber filler. I recently retrieved an engine that had been oiled and then left to sit in a barn with the head off for several years. I had to beat the pistons out of that one with a heavy hammer.
If it is siezed, try a big wrench on the front end of the crankshaft. You could apply as much as 200 lb-ft of torque if necessary without damaging the front pulley retainer nut. Otherwise you could remove the starter motor and try using a big pry bar against the ring gear to get it to break loose. You can apply a lot of leverage at that distance from the center of rotation, just don't break the transmission housing or the teeth on the ring gear. The rear plate on the engine is usually steel and will hold up to a lot of abuse.
If it breaks loose and turns so that the starter will turn it over, it was probably the rings rusted a bit to the cylinder walls. In this case, go ahead and crank it over on the starter to blow any fluid out of the cylinders through the spark plug holes, put one squirt of oil in each cylinder, install the spark plugs and start it up. Expect a huge cloud of white smoke out the exhaust for a few minutes until it clears out the cylinders. Once you get it up to running temperature, shut it off and give it an oil change and a fresh oil filter.
If it turns with the wrench but is so tight that the starter doesn't have enough power to spin it over, then it's probably fouled with varnish on the sides of the pistons. In this case you would likely be in for an engine tear down to clean the pistons, hone the cylinders and install new rings. Since you don't have much to lose here, it might be worth a little tinkering first. Put some solvent in the cylinders for a few days, then try towing it in top gear to see if you can get the engine to spin over and loosen up enough so the starter can turn it. If you do get it to run this way, you may expect the rings to be siezed and the engine may burn a lot of oil. Apply solvent liberally in the cylinders and let it sit for a week, then try it again. Drive it for a while, at least a few hundred miles, and see if the oil consumption goes down. If not, it will need new rings anyway.
If the engine is seized completely so you can't get it to turn at all, put a few ounces of solvent in each cylinder and let it sit for a while, like a few days to a week. Most any mineral based solvent will do, diesel fuel, mineral spirits, kerosene, paint thinner, WD40, Liquid Wrench, etc. Gasoline, alchohol, lacquer thinner, or acetone are not so good for this because they evaporate to quickly. Engine oil is also not a good candidate for this because it's a lubricator and not a very good solvent. If you can get the engine to break loose and turn after this soaking, you may get away without having to tear down the engine.
If it's still siezed after all this, it will have to come out for disassambly. Remove the cylinder head, flywheel, oil pan, all the main bearing and connecting rod caps, and remove the crankshaft. Then fashion a block of wood that just fits in the cylinder bore on top of the pistons and have at it with a five pound hammer to break the pistons loose from the cylinder walls. Do not push the piston down so far that the bottom ring drops out the bottom of the bore, or you may have a devil of a time getting it to go back up. If there is a noticable ridge at the top of the cylinder, you should use a ridge reamer to cut it back flush with the worn part of the cylinder before pushing the pistons out the top of the bore. If the piston rings are siezed and you force them up past a substantial ridge at the top lf the cylinder, you may damage the ring grooves in the piston.
Just in case you didn't know, all split bearing housings are bored in assembly, so the split line is never exactly on the center line of the bore. For this reason you must keep the bearing caps in order and mate them back in the original position in order to retain the correct bore size. If you were to mix up the connecting rod bearing caps, the engine would probably be siezed in some of the bearings when you reassemble it.
Let me know how you make out with this project. It's always nice to get an engine running without having to tear it apart.
Regards,
Barney Gaylord