AD31 still overheating!

[Hirdsp]

Getting really fed up with duff professional advice and find the forum has never let me down! It looks as though the over heating engine is kicking out less water than the good one, but plenty is still coming out of the culprit. It was the RCR engineer told me the bearings were shot, but then started quoting up to a £1000 to repair, draining the system and taking off the fan belts and another engineer told me Volvo didn't do kits and it had to be a new pump, so I came to the forum for some sense! The bearings looked fine but I swapped anyway along with the seapump kit. The engine still runs hot. I can draw water up through the pipes but it doesn’t let me put a hose down the pipe back out of the leg. This could be due to a one way valve?? Or should I suspect a blockage? Or maybe its just one of the thermostats and I'm barking up the wrong tree altogether. Would appreciate your thoughts. I have dual prop legs, but don’t know the make...it is a 1991 Sealine 305.

 

[Pendana]

With 1991 AD31's, I would guess your duoprop sterndrives will be 290-DP or perhaps DP-A's.

Overheating can be caused by numerous things but usually faulty thermostats in the fresh water side or some sort of restriction in the sea water side.

First, check that the fresh water level is correct, I recall the AD31's on my old Sunfury would overheat if just a couple of pints short.

You say that not so much water is kicked out by the engine (how do you measure that?) if that is the case, we would start looking for a restriction in the sea water flow.
Restrictions can occur due to blocked tubes in the heat exchanger, oil cooler or aftercooler and also the exhaust elbow can sometimes clog up. I would probably start at the heat exchanger but perhaps others who have suffered from this problem would suggest starting somewhere else.

Good luck

Eddie

 

[[2068]]

Some items mentioned already, but following the seawater system around, I would be checking:

- blocked outdrive seawater pickup
- collapsing inlet seawater hose between outdrive and transom shield?
- power steering fluid cooler (unlikely)
- worn seawater pump (faceplace, backplate, pump body worn?)
- heat exchanger (crusted up?)
- exhaust elbow outlet (has small holes, can get blocked)

It's a matter of following the system around and checking things out. Don't replace parts willy nilly unless you are reasonably sure you have found a problem, otherwise you can end up spending £0000's with no banana.

 

[baily]

Have you checked exhaust manifolds I had a sealine with these engines and had to have both manifolds replaced do to corrosion

 

[mickyb]

I too have 1991 AD31s in my sealine. I had one over heat on me..

It was due to a lack of coolant - basically it had been slowly leaking out and when the level was low enough - the engine boiled and the rest came out all at once.. whoosh splat.. the leaky area is the gasket between the exhaust manifold and the turbo.. BUT.... there is also a tiny pin sized hole in the exhaust manifold which is leaking coolant. Ive put some radweld type stuff in and have been running it fine and just keep topping the coolant up as it isn't losing much at all - think im going to take the manifold off and see if it can be welded.. if its corroded really badly then I guess i will have to replace it anyone know how much a new one will cost?

 

[[2068]]

>anyone know how much a new one will cost?

£750?

 

[dragoon]

When my 40's did the same, I went through everything before discovering that the oil cooler tubes were blocked. The reason this was last to check is that it's the most difficult thing to get to on my engines (low down, under the primary heat exchanger).

I'm not sure if you have such a cooler on the 31s, but if you do I hope this helps. It would certainly restrict the flow if they are blocked.

Another tip is to buy a cheap (infrared?) hand-held thermometer. I bought one of these from the US for $30 ready for the next time I had a cooling problem. You should then be able to measure the temperatures of the various coolers, pipe, elbow etc and compare between engines. I believe this may help you to identify the source of the issue (although don't quote me on this, as I've not done it yet : - )

Cheers,
Paul

 

[CX54WEK]

Could be a daft suggestion but a friend of ours who had similar problems with his Sealine found mussels in the water intake. It was restricting the flow enough to cause the one engine to overheat.

 

[laup]

Excuse my ignorance, but i have a pair of AD31's in my boat
How hot is your "overheating"?
What would be your normal running temp?
Does it go straight to hot or is it only after a bit of high workload?
I might have a similar problem!

 

[Peanuts]

Hi
As you have read there are many reasons for an engine to overheat, however without any background knowledge to the build up of this happening, apart from your impeller problem at Easter the checks have to start from the very beginning.

I know these have already been mentioned but this is the order I would start in so after checking the intakes are clear on the outdrive and the inside as far as possible I would be ensuring the rubber pipes are clear all the way through to the impeller pump. Don't forget the water intake nipple on the outdrive, if it is an aluminium one they can corrode up on the inside restricting the flow rate. Don't assume just because water is getting through it is enough, ensure it is clear.

Now you don't say which engine is overheating but I cannot help feeling it will be the stbd one with a power steering oil cooler, it is located under the starter motor, this is the first sort of restriction the incoming water comes to. This might be crudded up, just remove and clean out - sounds easy! One of those 5 minute jobs - not! Remember only one engine will have this cooler fitted.

That will do for starters and should keep you quiet for a while, let us know how you get on.

 

[mickyb]

Excuse my ignorance, but i have a pair of AD31's in my boat
How hot is your "overheating"?
What would be your normal running temp?
Does it go straight to hot or is it only after a bit of high workload?
I might have a similar problem!

Mine normally run at 80 - 85 degrees depending how far open the throttles are, sometimes nearer 90.. which seems about right..

As for how long they take to get there - depends on how soon you advance the throttles to a reasonable speed. I leave the marina at idle, do about 6kts down the dock channel and by then the temps are in the 60s-70s, then go full power to get on the plane and they soon go upto 80 - 85 degrees..

hope this helps

 

[volvopaul]

Hi sounds to me like it could be other things that have not been mentioned before.

As your motors are getting on in years now, the sytem corrodes away causing blockages in certain areas.

The oil cooler is the first port of call, if they are the originals and they are difficult to clean out as the enclosed inlet/outlet dont make it easy to rod all the tubes so the answer is remove the cooler.

You can rod out the heat exchanger easily, remove the end cap and look for crustation build up, if there are 3 or 4 tubes totally blocked that will make it overheat.

The intercooler will block up at the bottom, so take the top off, leave the sea water in, remove the plug at the bottom, if water stays in the tubes it blocked and slows down the flow.

The system should only work on flow, so place a pressure gauge in the system and record the pressure, caterpillar have ports to go into on all there engines, the max pressure is 3/4 psi anymore and the water is "stalling in the system.

Also rubber hoses on the suction side delaminate, they may look ok from the outset but collapse inside and suck together causing it to block up.

Lastly the exhaust elbow and riser through the transom shield can corrode away, and thats engine out time.

Plenty for you to look at,

What rpm does it overheat at?

I presume it boils over, have you carried out a sea trial with engineer with a hand held thermometer to actually see that the engine is high on temp, have you got the wires on the correct senders, ie overheat alarm sender and temp gauge sender, have you swapped them from engine to engine.

If your boat near the southcoast or midlands maybe you want me to take a look??

 

[Hirdsp]

Wow guys, your help is incredible as I am so miffed with many so called engineers at the moment. I may not be a Volvo trained engineer but I do have some idea of when I am getting taken for a ride. to answer the quenstions, yep it is the starbord so will look at that cooler and it is will over 90 deg and setting off the alarm, but heating much quicker than the port engine. Busy weekend ahead!