Acid flush in FWC cooled engine.

[StephenGwyn]

I have a FWC engine that had overheating problems. I installed a ball valve to override the thermostat and it now runs much cooler (170). However, when I point my infrared thermometer at the the engine, there is still a gradient across the top of the engine. The starboard side is 160, the port side, next to the manifold is 200.

Three related questions:

1) Is this normal, or should both sides of the engine be more or less the same temperture?

2) If it isn't normal, I'm guessing some de-crudding is in order. Does the acid flush help when only antifreeze (no salt water) has been running through the engine?

3) If I should do an acid flush, How do get rid of the acid? The instructions say that after the flush, you should run the engine for 15 minutes to flush the acid out of the block. That's fine if you have an ocean of coolant, but I don't want to use 15 minutes of anti-freeze.

Thanks,

SG

[hanleyclifford]

Originally Posted by StephenGwyn

I have a FWC engine that had overheating problems. I installed a ball valve to override the thermostat and it now runs much cooler (170). However, when I point my infrared thermometer at the the engine, there is still a gradient across the top of the engine. The starboard side is 160, the port side, next to the manifold is 200.

Three related questions:

1) Is this normal, or should both sides of the engine be more or less the same temperture?

2) If it isn't normal, I'm guessing some de-crudding is in order. Does the acid flush help when only antifreeze (no salt water) has been running through the engine?

3) If I should do an acid flush, How do get rid of the acid? The instructions say that after the flush, you should run the engine for 15 minutes to flush the acid out of the block. That's fine if you have an ocean of coolant, but I don't want to use 15 minutes of anti-freeze.

Thanks,

SG

It is normal for the port side of the engine to be hotter especially forward on the manifold. This can be mitigated by changing to the Tom Thatch Modification. An acid flush is ok but when finished flush with fresh water from a dock hose for a while. You can also use baking soda on the last flush to neutralize the acid. Sounds like you have a late model with double acting thermostat - trouble. IMHO lose the thermostat altogether and use the ball valve to control temp. I run my FWC engine at 160 and on up to 185 when really working.

[BunnyPlanet169]

I have no data set other than my one engine, but I strongly believe there will be some gradient across the head based on the design of the cooling jacket, and that it will be biased as you said. The manifold side will be hotter if only because coolant enters the other side first. That alone wouldn't be enough for me to start thinking about acid flushing.

The manifold itself does not cool well, enough so that it has it's own acronym, UHS (the ubiquitous hotspot), where paint routinely burns off. The Thatch plumbing may help, and will reduce the possibility of having an air pocket form at the higher front end. YMMV.

I have a FWC engine that had overheating problems.

Was it always FWC? By you, PO, or factory always? Assume from your description it ran OK at some point under your ownership...

I installed a ball valve to override the thermostat

Think about what's happening. The ball valve restricts water that would go via the bypass over the top of the thermostat to instead go through the block and then through the thermostat. The thermostat doesn't know or care....

The fact that you had to do this suggests some blockage, but it might be a simple as a stuck or faulty thermostat. The first thing I'd suggest would be to pull the thermostat out and see what's in there. It's 5 minutes and 1 or 2 gaskets.

Try running as Hanley suggested without the thermostat at all using only the ball valve. Then you'll have some data that says a) it's better, or b) I need to think about acid.

[StephenGwyn]

My boat has been FWC cooled as long as I've owned it, since 2003. I'm guessing the guy I bought it from didn't do it, since he was a knucklehead, but the guy before him seems to have done things properly, based on things I've found on the boat. My guess it was RWC for the for the first 15 years of it's life and then 25 years of FWC.

When I close the ball valve, the manifold warms up from 130 to 150. It seems uniform the length of the manifold. The head of the block cools from 225 to 200 on the hot side and 190 to 160 on the cool side. Back of the head is slightly cooler than the front.

I suspect blockages because the fresh water impellor has started failing fairly frequently with blades breaking off, indicative an increased load. But it could be wear on the pump which leads to vibration which an increased failure rate.

I guess my question is: What am I trying to dissolve with the acid?
Since the coolant is pre-mixed antifreeze, I don't anticipate a lot the precipated crud associated with using saltwater or anti-freeze mixed with tap water. Is the acid attacking the rust?

Thanks,

SG

[JOHN COOKSON]

Originally Posted by StephenGwyn

I suspect blockages because the fresh water impellor has started failing fairly frequently with blades breaking off, indicative an increased load. But it could be wear on the pump which leads to vibration which an increased failure rate. SG

Is there a piece of broken impeller somewhere in the fresh water side plumbing?
That would certainly "increase the load" and reduce the FW flow.

TRUE GRIT

[hanleyclifford]

If you have unrecovered pieces of impeller in that block you need to get them out. It is also useful to run a strainer in the loop, at the cool end just before the pump intake. Thermostats are among the worst flow restricters in an engine. It would not surprise me if you found impeller bits in the thermostat. My hunch is that losing the therrmostat will solve your problem.

[BunnyPlanet169]

Originally Posted by StephenGwyn

I guess my question is: What am I trying to dissolve with the acid?
SG

Muriatic acid is used to eat rust.

http://www.thechemicalblog.co.uk/removing-rust/

Again - given your description - you really ought to think first about looking inside the thermostat housing.

[StephenGwyn]

I'm pretty sure there are some impellor bits stuck somewhere, but I've checked all the hoses. They might be deep in the heat exchanger. I have a strainer just before the pump. When I clean it, it rarely has more than a few bit of crud in it.

Investigating the thermostat is on the agenda, once I get some gaskets.

Stephen

[hanleyclifford]

Originally Posted by StephenGwyn

I'm pretty sure there are some impellor bits stuck somewhere, but I've checked all the hoses. They might be deep in the heat exchanger. I have a strainer just before the pump. When I clean it, it rarely has more than a few bit of crud in it.

Investigating the thermostat is on the agenda, once I get some gaskets.

Stephen

If you have a strainer and are catching little with it my guess is you have slow flow in the system probably caused by the thermostat and anything that might be hung up on it. I recommend that you do nothing about the flush until you have run the engine a few hours sans thermostat. It is important to have a good impeller. Coolant velocity is the name of the game especially when it comes to avoiding crud build up. Watch that strainer start to fill up.