Engine Overheating

[Lucky]

Would you agree with me that the following is an impellor problem ??

My starboard engine overheats after a little time. The impellor housing is hot along with the two heavy duty pipes that run to it - unlike on the starboard engine where all is cold.

(Ignore the bit about the connector)

One of the pipes takes water from the broads, through the impellor and filter, then circulates this around the cooling system (the green stuff with anti-freeze) to keep it cool. I'm hoping I am correct so far - I'm very much learning !!.

So, in theory, the impellor housing should not ever get hot as its taking water from the broads.

Now, if I unscrew the black cap on the raw water filter and quickly start the engine, then stop it, it is obvious that the impellor is doing its job and water gushes out. Could this 'gush' out if the impellor isn't turning ? If this 'could' happen then I think this is the problem - but I presumed that the impellor is for exactly that, and if it wasn't turning there isn't anything else that would make the water gush...

Any ideas ?

[Guest]

Is the raw water filter above or below the waterline?

[Lucky]

Very much above..

[Guest]

Very much above..

sorry, just edited my post. I meant to ask about the raw water filter.

[Lucky]

Yep, still above !! lol !!

[Guest]

As the impellor cover looks very accessible (makes a change), I'd take it off and have a look at the impellor to confirm what you think. IME, the impellor will either have broken vanes, disintegrated or stuck in the housing.

HTH

[Guest]

Hi luke,

I have had this problem many a time...and ruined a huge number of impellors during the learning process!

The best way to check whether the impellor is doing its job is to simply put your hand on the water pump housing and the exhaust elbow. Both should be stone cold if the water is circulating. If the water pump is at all warm, that will be friction from the impellor. They do not last more than minutes in these circumstances in my experience.

As already suggested, I would check the impellor is still intact. We often experienced a problem after replacing an impellor where the water pump still didnt "self prime" although they should. The way to get around this is to fill the sea water filter housing with more water as you may have air trapped between the incoming pipework and the pump. This normally works and the advice was given by Northgate Marine (Volvo). As your pump is above the waterline, there shouldnt be a problem with sinking the boat!!!

Any probs...give me a call...

adam aka LB : : :

[Guest]

Ditto what the man says. The impeller in the pump shown is before any engine cooling actually takes place. Consequently it should be cold at all times. If it gets how then there is no water circulating and the impeller will last minutes at best.

I've not yet encountered this problem on our current boat but on our last boat the problem was resolved / avoided by priming the raw water intake. Open the strainer housing and pour water down the pipe which comes from the raw water pump until it comes up to the top of the pipe. Replace the strainer and the cap and then start the engine again.

I can't swear it will work on these engines as the strainer / pump layout is somewhat different but it can't hurt to try. You might also want to consider changing the impeller as it sounds like it's probably been ruined by being run dry.

[diesel falcon]

to illustrate the discriptions

[Guest]

Luke...

Another point...always keep spare impellers on board!! Its not unusual on the broads for the water intake in the leg to get temporarily fouled causing an overheat.

At over £40 each for volvo impellers, I buy an italian equivalent from the guys below on e-bay for a lot less money

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

Although in some ways we are lucky that our sea water filter is positioned after the pump (as opposed to before in the diagram above), this gives us the luxury of not having to remove the heat exchanger to recover "impeller bits" when they shatter (as our sea strainer catches them first), however, when they do shatter, often the debris drops back into the intake pipe. Consequently, when your new impeller is fitted, it can become damaged by bits of debris being sucked into it.

Last time it happend to me...I was still catching debris in the sea strainer 6 weeks afterwards!!! Again...it was the helpful man at Northgate that gave me this tip after about the third replacement impeller : : :

Touch wood...its not happend since...

LB

[Antares_9]

Luke, you say that the strainer is above the waterline and that water is being pumped out of the top when you temporarily remove it, ergo we can positively conclude there is water in there lubricating the impeller and it is indeed capable of pumping. It may not be pumping enough of course but it is pumping. Obviously the first thing will be to remove the impeller cover and have a look, especially as you have access that can only be dreamed of on some installations. The established fact that it is both pumping and there is water to lubricate it leads me to suspect the possibility of a blockage somewhere after the strainer and impeller which when the easy path (replacing the cap) is removed is preventing circulation. The usual suspect in such cases is where the raw water is injected into the exhaust elbow. I could of course be that the impeller is shagged as far as pumping against a restriction is concerned but able to pump when the cap is removed and there is less restriction, as has been already said, have a look at the impeller as a first call.

[Guest]

Good point David...

and I will add that when we pulled Jupiter mist out of the water for the first time at the end of 2008 season, whilst it had not overheated, there was almost nothing left of the impellers.

lb : : :

[Lucky]

Firstly, thanks for all the advice !!!

Now, I am a little confused.... As David said, when I take the strainer cap off and start the engines it appears to be pumping water normally - I say normally but obviously I don't actually know what normal is !! Therefore, the impellor must be doing its job ?

A couple of you have said about the exhaust elbow - I know I'm going to sound really stupid, but what is this ?

IF there is an air block or something that has got in there somewhere - why would the impellor housing and associated pipes get so hot ? If there is a blockage, then the water just wouldn't move surely ? Reading this back to myself I know I sound stupid, but I just can't get my head round it..

Its too dark out there now to start taking bits off, so I'll have a look again in the morning....

By the way, I should of mentioned that the boat had a full service last week, including of course the impellors. Also, not sure if I mentioned that both pipes going to the califior are hot also..

[Antares_9]

By the way, I should of mentioned that the boat had a full service last week, including of course the impellors.

In that case, call the man who did it and get him to have a look before you even touch it.

[Lucky]

Done that David, they will be coming out next week. I was just hoping that it possibly could be something simple that I could take care of myself - you know, missing something very simple like checking the strainers for a blockage - cause I know how to do that !!...lol

[senator]

The exhaust elbow sits on top of your manifold Luke but if you are taking it off you need a new gasket. they do have a habit of corroding so it could be rust.

Were all the vanes still on the impellers you took out? if not you may be about to find the missing bit.

[mbird]

Luke, when you say the impellor was "pumping normally", how much water got ejected? When I mistakenly tried to winterise our engines by pouring antifreeze into the weed filter (like I used to on the BMC in our old boat), even when just being cranked, the water shot out of the top of the strainer by about a foot!

Just as a bit of lateral thinking, might be worth raising the leg on the affected side and see if there is a plastic bag or anything obvious like a pair of Cols' pants, stuck over the water intake (which is at the front of the leg. inline with the propellors).

[Guest]

Now, if I unscrew the black cap on the raw water filter and quickly start the engine, then stop it, it is obvious that the impellor is doing its job and water gushes out. Could this 'gush' out if the impellor isn't turning ? If this 'could' happen then I think this is the problem - but I presumed that the impellor is for exactly that, and if it wasn't turning there isn't anything else that would make the water gush...

Any ideas ?

Somehow I missed this entire paragraph when replying - so you can safely ignore what I said!

[Lucky]

Yes, all the vanes were there on the old impellor. In fact on close inspection they both seemed in good order. It wasn't until you bent them that you could see there was a couple of cracks, result of wear. Nothing missing though.

I'm presuming that the exhaust elbow is "B" not "A" am I correct ?

[Lucky]

Luke, when you say the impellor was "pumping normally", how much water got ejected? When I mistakenly tried to winterise our engines by pouring antifreeze into the weed filter (like I used to on the BMC in our old boat), even when just being cranked, the water shot out of the top of the strainer by about a foot!

Just as a bit of lateral thinking, might be worth raising the leg on the affected side and see if there is a plastic bag or anything obvious like a pair of Cols' pants, stuck over the water intake (which is at the front of the leg. inline with the propellors).

No, it is a good suggestion Mark and something we looked at ... Nothing appears to be fouling on the leg.

[mbird]

No Luke, A is the thermostat housing, and B I think is probably something to do with your supercharger? (not sure on that one as I ain't got them on my lumps!).

Assuming your engines aren't too dissimilar to mine, the exhaust elbow will be at the back of the engine, and bee a steel pipe about 4" diameter. It will have a smaller pipe going into the top of it, which is where the raw water exiting the heat exchanger will be injected into the exhaust gases before they go out through the transom shield and out to the outdrive.

[mbird]

Ah, found a sketch of the exhaust elbow as it exits the turbo.

scan.pdf

[Guest]

luke,

It is so similar to the problems we had on Jupes and my guess is that it is something simple. If you bear in mind that the problems we had with Jupiter mist started AFTER we replaced the very worn impellers, and it was the remaining debris and the lack of fully priming after replacement that caused our issues. So, in a way, I am not surprised that even after a service, this might happen. (Having said that, one would assume that whoever replaced the impellers should have immediately started the engines and checked that the pump/elbow etc all stayed cool). It literally only takes a minute or so for the pump to get hot if there is a problem, and if there is a problem it will be less than minutes before the impeller becomes damaged.

Not sure which engines you have, but my exhaust elbow is the bit connected to the turbo. As its on the raw water circuit, it should always be as cool as the outside water going in to it.

Seeing as it was just serviced, I am sure they will sort it for you, but if not for any reason, check the impeller part number and if its the same as mine, I have 3 on board and happy to pop over and see if we can sort it.

lb : : :

ps just seen marks post...what engines do you have and we can get a schematic diagram!

[Guest]

doh! Mark is ahead of me!!!

[Lucky]

Do you know I sometimes wonder whats happening with my memory Mark !! I learnt all about the supercharger last week and I know where it is !!!

This is the best picture I have of that engine, and looking at it I am presuming that the exhaust elbow is going to be a pain to get to..