Cold Engine

[Patience]

I have replaced the thermostat in my A4 as it would not come up to temperature. I checked the engine to confirm and it was cold. I reasoned that the thermostat must be stuck open.However after replacement the engine still will not come up to temp. The manual advises not to restrict the raw water intake, but I closed the valve half way to learn the result. The engine then slowly warms up. I believe the engine is supposed to run between 140 and 160 degrees. Is it possible the new thermostat is defective?
Please advise.
Thanks

[Don Moyer]

The thermostat could be stuck open, but I'm suspicious that there might be something else going on, since you're having the same result with two different thermostats. You can resolve the thermostat question by removing it and trying to breathe through its operating mechanism. As long as it's difficult to blow your breath through the thermostat (cold), it should be OK.

With regard to limiting the flow from the pump as a temporary fix, you could install a simple ball valve in the hose leading from the manifold to the exhaust system. However, flexible impeller pumps do not tolerate restrictions on their suction side very well so I discourage the use of your through-hull valve to control your temperature.

Here is a tech tip we prepared on the subject of overcooling that may help:

"There are really only three things that can cause engines to run cooler than the thermostat rating would indicate:

1) Water is getting through a partially stuck open thermostat.

2) Water is somehow getting around a properly functioning thermostat.

3) The gauge or sending unit is malfunctioning (usually the least likely).

The first two of these possibilities are sometimes aggravated by a partial restriction within the by-pass loop (between the "T" fitting in the center of the water jacket side plate and the inlet to the thermostat housing).

It's rather difficult to visually inspect the current thermostats from Westerbeke without the "breathe through" test. When looking in from the top of the thermostat, the moveable disk may appear to be down and closing off the opening in the center of the housing, when in fact, it's raised off the
housing by 1/16" or so.

In terms of the second possibility, water can sometimes by-pass around the base of a thermostat if the top of the head (where the thermostat seats) has eroded away to some extent. In these cases, the overcooling can be remedied by installing a spacer under the thermostat. If you find this fix to be necessary, you will need to replace the two thermostat housing studs with manifold studs. The manifold studs are slightly longer, and accommodate the thickness of the spacer.

Relating again to the second possibility, water can move around the base of a properly functioning thermostat if the groove around the base of the thermostat housing is eroded away, leaving the thermostat to rise up slightly off its seat.

Regards,

Don

[Patience]

Thanks Don,
I had a suspicion that corrosion may have been the problem.When I removed the old thermostst I found a good amount of black corroded metal in the head. Do you offer a "Kit" to remedy this problem, or some directions.
By the way I finally got around to installing the oil dipstick kit I purchased-I am very pleased with it.I purchased the remote water pump lube kit, which I
will install sonn.
Thanks for your reply

[Administrator]

Your engine would probably benefit from an acid flush or pressure washing. We do offer a kit to facilitate pressure flushing (with instructions included in the kit) in our online catalog at moyermarine.com.

You could also perform an acid flush before pressure flushing. Here are the instructions for acid flushing, taken from our service and overhaul manual:

CAUTION: Be sure to wear proper protective clothing (including eye protection). Always add acid to water when mixing, and if possible hang a bucket over the exhaust outlet to catch acid solution when discharging from boat.

1) Mix 1/3 gallon of household muriatic acid (30% concentration) into a 5 gallon bucket of water.

2) Draw the entire 5 gallons of acid solution into the engine through an inlet "T" fitting between the raw water through-hull and the inlet to the raw water cooling pump (the same "T" as used for winterizing the engine). For best results, thermostat should be removed and the by-pass hose temporarily clamped off. All the acid solution will then be pumped through the block by running the engine. Stop the engine as soon as the bucket is empty.

NOTE: Some of the acid solution will find its way into the exhaust system, which might loosen up any crud that may have built up within the water lift muffler and connecting plumbing.

3) Start the engine after letting the acid set in the water jackets for about 15 minutes and run it long enough to thoroughly flush out the acid.

4) If it has been possible to retrieve the acid solution from the back of the exhaust system, add approximately 1/2 pound of household baking soda to five gallons of acid solution prior to discarding.

Regards,

Don

[Patience]

I took your advive and removed the side cover to inspect the tee fitting. There was no blockage, I flushed out the water jacket and cleaned it futher with a mild acid solution I picked up at the hardware.I also removed the thermostat gave it the breath test (it passed ) and reinstalled it with a newly purchased housing from Moyer Marine. While I was busy with all this I noticed the heater hose running from the heat exchanger to the exhaust manifold. It is 5/8" diameter hose, not 3/8" as the manual states.Then it dawned on me that I had the yard mechanic replace the exhaust system last year. I got a large plastic clamp from Home Depot and compressed the hose about 1/2 its diameter. I remembered you suggesting a small ball valve to regulate same.The engine then came up to temperature.
The water must be exiting to quickly through the by pass because of the larger diameter hose. I will replace the 5/8'" with 3/8" and the problem should go away. Thanks for your help.