Engine temperature down

[Unregistered]

My late model Atomic 4 was acid flushed earlier in the season per your book. The engine ran fine and was cool. After a month or so the engine temp went up. I recently added the restrictor valve and changed the plugs. When I ran the engine the temp was down considerably (around 120). As I inspected the engine, I found what appeared to be water bubbling around spark plug #3 with a white powder forming around the base of the plug. There also appeared to be steam coming from the exhaust that had not happened before. This engine is raw water cooled and has what appears to be plenty of water flow out the exhaust. Any ideas?

[Don Moyer]

The elevated temperature which was quickly remediated by a restriction in your bypass loop was probably nothing more than a bit of crud becoming lodged in the "T" fitting in the middle of your water jacket side plate. The fact that you still have plenty of water flow out of the exhaust indicates that the pump is working fine and that there is no unusual restriction in the cooling passages. Otherwise, your total flow would be reduced out of the back of the boat after you installed the restrictor valve.

Water collecting around the base of a plug usually comes from a small leak from one of the studs that seeps back on the top of the head until reaching one of the recessed areas around a plug. The white deposit is from the minerals (possibly salt) that precipitates out of the water.

Steam from the exhaust, in an engine that has plenty of water flow out of the exhaust, is frequently an indication of a small crack in the manifold or (worse) one of the exhaust ports in the block. Steam also frequently generates within the exhaust system itself when precipitate builds up where water is introduced into the hot section.

I would do a couple of things in the following sequence to address each of your three symptoms:

1) Remove the hoses from the front and rear of the manifold and then pressurize the manifold by holding a finger over one end while blowing into the other end. You may have to blow quite hard to find a very small crack, but in most cases a leaky manifold will be found quite easily by this simple method. If the manifold leaks, it will need to be replaced.

2) If the manifold checks OK, reinstall the hoses and squeeze the hose from the rear of the manifold to restrict the flow of water while running the engine. The added pressure within the cooling jackets of the engine should enable you to discover where the leak is located that is finding its way to the recessed area around the third plug. Small cracks on top of the head can usually be sealed using one of the small fiber glass repair kits from West Marine. If water is seen to be seeping up through one of the studs, the stud will need to be removed and resealed.

3) Remove the hot section of the exhaust (between the back of the manifold and the inlet to the water lift muffler) and inspect for a large build up of crud where the water enters the hot section.

4) If there is no restriction within the hot section to explain the steam, remove the manifold and inspect the exhaust and intake ports in the side of block. Look especially closely at the exhaust ports (one at each end and two in the center of the block). If there is a leak in one of the exhaust ports there will usually be rusty discoloration in evidence.

5) If no other source of the steam from the exhaust is found (manifold OK, hot section of the exhaust unclogged, and no obvious signs of water from any of the exhaust ports), I would do a simple pressure check of the block and head.

The easiest way to pressure test the block (without removing the head) is to first plug the outlet of the thermostat housing. Then remove the hose from the outlet of the water pump, and install a hose barb, a threaded coupling, and a Shroeder valve in the end of the hose, so that a standard bicycle tire pump with a built in pressure gauge can be used for the test. A Shroeder valve is the standard valve used on automobiles, and they are available at any auto parts store. If no bicycle tire pump is available with a pressure gauge, you can install a "T" fitting ahead of the Shroeder valve to accommodate a pressure gauge. The block should be able to hold 20 psi for an hour or more without a noticeable drop in pressure.

NOTE 1: It would be preferable to remove the manifold for the above pressure test so that the valve ports can be inspected during the test. If, in removing the manifold, one or more studs unthread from the block, you will have to reinstall the studs to prevent air from leaking out of the cooling jacket during the test.

NOTE 2: In many cases, it is preferable to drain the water out of the block and head for the test and listen for an air leak. Small leaks in a combustion chamber (particularly the combustion chamber of the head) can usually be heard through the spark plug hole.

If pressure decays rapidly in the block and head, look for water leaking out though one or more exhaust or intake ports. If water is leaking from an intake or exhaust port, it may be impossible to see exactly where the water is originating, but a defective block would definitely be indicated and the block would have be removed from the engine and taken to a machine shop for evaluation.

Best regards,

Don Moyer