Fairline Holiday Club

[Sonya Falconer]

Hi Guys

Thought we had cured the engine overheating problem but it is acting up again. It will run all day at 1000rpm and sit at 140degrees but as soon as we go over that speed the temperature starts to climb and when we lower the speed back to 1000rmp the engine cools back down.

I know that it is the same boat and engine as Tony's, AQ200d, the only diffrence being we have a fresh water heat exchanger fitted (before we bought the boat). My question being, could we do away with the fresh water cooling system and convert it back to raw water cooled and what would this involve.

Any help would be greatly appreciated as we have had this problem most of the year and it is really spoiling what should be an enjoyable experience with our first boat.

many thanks

Sonya/Joe

[Gary]

Hi Sonya,

Before you go taking off the heat exchanger (which in my opinion is far better than raw water cooling) I would carry out a few simple checks.

It could well be that the problem lies outside of the heat exchanger.

1) Firstly the heat exchanger will have a removeable tube stack, usually between the 2 large rubber end caps on the manifold. Take this out (which should be done regularly anyway) and make sure it is clean and debris free.

Then flush fresh water through the heat exchanger with the tube back in place.

If all this is clean and water flows well then it is highly unlikely the heat exchanger is the problem and that converting back to raw water will not solve the problem.

2) Next make sure the ignition timing is not too advanced, this will cause overheating as soon as load is placed on the engine.

3) next flush fresh water through the engine the flow should be fast and unrestricted, if it is then flush the engine with a proprietory cleanser to improve flow.

4) If the engine flushes ok the check the raw water pump impellor, or remove the return hose that goes to the outdrive, run up the engine an see how fast the water comes out, it should be a fast constant flow.

5) Assuming the above is all good then check the flow of water around the engine, this is provided by the engines internal water pump, In order to this remove the pipe from the heat exchanger where is goes back in to the engine block, again the flow should be constant with the engine running.

6) If all the above seems to check out then there is a slim possibility the head gasket could have blown between the cylinder and water jackets in the block. Normally this would show up as you would lose water from the header tank on the heat exchanger.

If you were to revert back to raw water cooling then the only part you will need to source is the original exhaust manifold as fitted to the AQ 200 engine, this will replace the heat exchanger/exhaust.

I am assuming you have removed the thermostat? If not try this first.....If you are unsure of any of the above or you would like me to talk you thorough it when you are next at the boat please give me a call on 07990 801862.

Hope this helps

Regards

Gary
_________________
Life is better on a boat!

[Sonya Falconer]

Hi Gary

Thanks for the reply.

1. We have cleaned out the heat exchanger, all was well there
2. Not checked the ignition timing yet
3. Have flushed water through the engine and it is ok, water pours out
4. Have renewed the raw water impellor
5. Not removed the pipe from the heat exchanger for the fresh water yet
with the engine running.
6. Not losing any water from the header tank.

The part I need for the AQ200D is the thermostat housing directional unit, the part number is 855485. The heat exchanger isn't connected to the exhaust manifolds, these are the original Volvo Penta ones, it is just the pipes from the exchanger to the engine etc.

We have tried everything else. Renewed the exhaust manifolds, thermostat, impellor. It will sit all day at 1000rpm at 140 degrees but as soon as we go up to 1500rmp the temperature starts to creep up to the red and the exhaust risers are extremely hot to touch and if we drop the speed back down the temperature creeps back down to 140 degrees. This is why we thought that the heat exchanger wasn't letting enough water around to cool the fresh water.

It is a weird set up as it seems like the sea water goes through the tubes inside the heat exchanger and the fresh water goes around the outside of them, where I thought it would be the other way around.

any help much appreciated, thanks Gary

Sonya

[Gary]

Hi Sonya,

I must admit I did not read your post fully, I now understand the type of heat exchanger you refer to
If the exhaust manifolds are getting hot this can only be a poor water flow on the raw water side.

If the raw water pump impeller is new then the obvious conclusion would be a restriction somewhere in the system. The most likely area would be the tubes inside the heat exchanger.....you are right..it does seem strange that the raw water flows through the tubes rather than around them but this is how they all are.

So....are the tubes clear, I appreciate you say you have cleaned the heat exchanger, did this include inside the tubes?

If so then the raw water should flow freely through the tubestack. I note you say you flushed water through the engine, but this would be the freshwater circuit as things are at present, I do feel that the issue has to be on the raw water side if the exhaust manifolds are getting hot as I assume they are cooled by the raw water before being exhausted through the outdrive.

So it seems that the higher the revs and therefore load on the engine the less water we are getting, my guess is that this is going to be a hose collapsing internally. I saw this quite a lot during my technician days in the automotive industry.

What happens is that as more water is trying to pass through the hose the pressure increases causing internal wall of the hose to act as a flap and thereby restricting the flow when most needed.

I am confident it will be on the raw water system due to the hot manifolds so have a feel for hoses that are soft or look ancient and try to bypass them. It is a liitle trial and error I'm afraid but if everything else checks out then I am at a loss to think what else it could be.

Good luck !!

Gary
_________________
Life is better on a boat!

[Sonya Falconer]

Hi GAry

Thanks for the quick reply. We havent checked the hoses. Could be worth a try. Weather permitting we are going to take her out on Saturday and will check all the hoses when the tempeature builds up. Must admit we havent replaced any of the hoses.

will let you know how we get on.

thanks again

Sonya

[Tony]

Sorry for late reply, ive been away.

However in a previous post I had asked if you had checked all rubber hoses, and you confirmed yes
http://fairlineholidayclub.co.uk/Forum/phpBB2/viewtopic.php?t=974

In your reply to Gary you say you havnt checked and "Its worth a try"
Im just a bit confused now.

Tony
_________________
...there is NOTHING--absolute nothing-half so much worth doing as simply messing about in boats...

[Sonya Falconer]

Hi Tony

Sorry about that. We did check them but not when the boat was running and they were hot/warm. Will check them on Saturday and let you know. Joe is still thinking of converting to raw water cooled. What do you think ??

Sonya

[Tony]

Sonya

If it was my boat and I was using it in a salt enviroment Id rather it was fitted with a fresh water heat exchanger.
If its goosed the ideal would be for me to replace it, but they arnt cheap.
If I couldnt afford it yes id consider removing it and reverting to original raw water intake cooling.

Head gasket not blown? Fairly obvious if it is, water all over the engine when running at operating temp, i.e in the green on your temp gauge

By the way, when you replaced the impellor did it come out complete and intact, no veins missing when you removed it??

Check the hoses are not soft and collapsing in to restrict water flow...also bring her up to temp.Keeping the boat in neautral, lift the leg until the exhaust comes clear of the water.
You should be able to see water burbling out of the main exhaust. This is the exhaust that vents via the cavitation plate (the flat horizontal bit above the prop..sorry if I sound like a prick, but some folk dont know)
Now, while still in neutral push in the red button on the side of the throttle so you can rev the engine in neutral
As you rev the engine (no need to go above 3500-3800 on each pump of the gas) you should see water SPEW/SHOOT/JET from the exhaust to about 15-20 feet?
This will be the raw water passing through UNRESTICTED,. Does it?

Cheers

Tony
_________________
...there is NOTHING--absolute nothing-half so much worth doing as simply messing about in boats...

[Sonya Falconer]

Hi Tony

Haven't noticed water coming out of the exhaust when we rev it up in neutral. It comes out of the vents on either side of the leg. Joe has taken the spark plugs out and there is no water on them so dont think the head gasket is blown. The engine runs no problem, doesnt splutter or anything.

We did price the heat exchangers and yes they are quite expensive. Also priced the thermostat housing and this is going to cost about £250 so either way it is going to be costly. We just dont want to spend any more money to find out we have the same problem.

Will test the hoses when they are hot and let you know on Saturday, hopefully it is something as simple as that.

thanks again for the help

Sonya