solution for cooling problem aq170 b30

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turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

solution for cooling problem aq170 b30

Inlägg av turbotuur » 04 nov 2014, 11:10

Dear fjord owners,

For everyone still running the aq170 and finding cooling unreliable even after closing out all the obvious and all elements brought in good shape:

I found a solution for cooling problems on the volvo penta aq170 b30 engine.

Of course al the obvious things have to be checked, but sometimes this does not solve the problem. I found out the thermostat cover contains a small hole in the center which allows coolingwater to bypass the engine with closed thermostat.

I was used to the ford watermota engines having a spring valve in the bypass making sure all water will go trough the engine when the thermostat opens. In case of the aq 170 the bypass remains open untill the thermostat is fully open and hits the housing closing the bypass.

One of my engines with the most stable behavior had a 7,5 mm hole, the one with less stable behaviour had a 8,5 mm hole (probably the result of 40 years of corrosion / erosion).note the hole starts large,having the smaller diameter at the bottom.
The spare one in the shed had a 7 mm hole.

I placed an insert with a 6 mm hole in it with amazing results! The engines temperature stays at thermostat temperature of 55 deg to 60 under almost all circumstances. It seems scarry low at first, but the minimum operating temperature is well mainained.

It seems when volvo penta calculated this bypass restriction 45 years ago it was ok on a light fouled an corroded engine, but after over 40 years the hole becomes bigger and the engine itself becomes more restrictive.
This is forcing the water to exit without entering the engine and less and less water wanting to follow he more restrictive path trough the engine and taking the becoming more easy way out through the bypass hole.

Important notice:

Make sure the insert is absolutely tight to the housing as you do not want to have wandering elements in the cooling system resulting in blockage and overheating

Do not use a smaller hole than 6 mm as this will restrict bypass waterflow resulting in overheated exhaust / manifold. If you have doubt start with a 6,5mm hole (which could be the original size????) and go down up to 6 mm minimum untill stable behaviour is obtained( measure the current size of the hole and reduce in small steps untill stable behaviour close to thermostat temperature is obtained). It is al about the ballance between motor flow resistance and bypass flow resistance. In optimum the hole should be as big as possible obtaining the stable behaviour. Going from 7 mm to 6 mm will allready result in a 25% reduction of the flow area of the bypass.

Of course this solution is an add on for having all other items part of the cooling system in good working condition, not a replacement.

I am inrerested in the sise of the bypass of other aq170 owners.

Good luck!

Lars Lundbladh
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Re: solution for cooling problem aq170 b30

Inlägg av Lars Lundbladh » 04 nov 2014, 16:14

Hi,

I only know the behavior of the fresh water cooled AQ170 engine where the standard procedure is to fit a restrictor tube in the circulation pump. Also a hole should always be drilled in the thermostat 2-3 mm to get a constant flow of water through the thermostat.
A good description on the freshwater cooled system for AQ170 you can find here:
http://www.martec.se/shop/31500/art76/1 ... 1vp170.pdf

/Lars
Fjord 900 Dolphin -88 /D6
Ordförande och webmaster i Fjordklubben

turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

Re: solution for cooling problem aq170 b30

Inlägg av turbotuur » 04 nov 2014, 16:48

When placing a restrictor in the circulation pump, where should it be located, suction or discharge side and what size?

I still wonder what the original size should be of the thermostat cover bypass because it made a tremendous difference on both engines by reducing the size of this bypass. It should anyway be brought back to its original size to make the system work as it is ment to from the beginning. I have seen three housings so far but all have serviced open cooling for over 40 years with corresponding corrosion. Whit this 6 mm restrictor it works verry good but perhaps 6,5 should be the original size.

Lars Lundbladh
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Blev medlem: 26 jul 2003, 23:46
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Re: solution for cooling problem aq170 b30

Inlägg av Lars Lundbladh » 04 nov 2014, 19:36

Do you have the fresh or raw sea water cooling?

The restrictor Is facing cylinderhead, if I rember correctly it is about diameter 6 mm.
Fjord 900 Dolphin -88 /D6
Ordförande och webmaster i Fjordklubben

turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

Re: solution for cooling problem aq170 b30

Inlägg av turbotuur » 04 nov 2014, 19:47

I have the original seawater cooling

Lars Lundbladh
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Re: solution for cooling problem aq170 b30

Inlägg av Lars Lundbladh » 04 nov 2014, 20:08

There is a great difference I between seawater and fresh water cooled systems, as thermostat hosing and circulation pump differs. I guess the hole diameters you are referring to is the holes in the thermostats hosing itself?

In what whay will the temperature be more stable?

Thanks for sharing your findings as this could help other to detect faulty engines.

/Lars
Fjord 900 Dolphin -88 /D6
Ordförande och webmaster i Fjordklubben

turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

Re: solution for cooling problem aq170 b30

Inlägg av turbotuur » 04 nov 2014, 23:51

Indeed its about the center hole in the thermostat housing of the original sea water cooling.

The temperature will stay close to thermostat temperature around 55 to 60 instead of a quarter to half way up the guage.

With a hole of 7,5 and clean and good shape engine it will work ok, but you will see big fluctuations in temperature when returning to idle or giving more power. In case of my other engine with 8,5 mm it was impossible to get the guage down half way. Even after bringing the engine in almost new and clean condition.

With the 6 mm insert both engines perform exactly the same. I can send you pictures of the housing and temperature gauge reading if requested.

turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

Re: solution for cooling problem aq170 b30

Inlägg av turbotuur » 05 nov 2014, 19:12

Tried 6,5 mm today (started with 5, 5,5 and 6) on both engines. temperaure comes up a bit higher about 3 to 5 degrees. A bit more fluctuation when going on / of trottle. Also a bit more difference beween the engines compared to 6mm. Looking at the current water temperature it is best to see how it acts in the summer to see if 6,5 is small enough. The temperature gauge comes up between 55 and 65 degrees when going of trottle with warmed up engine. I think it is possible to conclude if the hole is bigger than 6,5 instable cooling behaviour becomes more likely. Varying from 5 to 6mm did not make a differens, the remperature gauge will stay close to thermostat temperature and both engines act exactly the same. To small hole will generate more back pressure on the seawaterpump so 6 mm should be used as a minimum. I keep the 6,5 for now and see how it does allong the new boating season. For now very pleased with the results! Cooler engines than ever before!

When placing an insert, keep 6mm as a minimum, if you think its operating to cold make it 6,5 to have a 3 to 5 degrees higher operating temperature

hpotgieter
Inlägg: 2
Blev medlem: 06 dec 2019, 21:24

Re: solution for cooling problem aq170 b30

Inlägg av hpotgieter » 07 dec 2019, 17:20

Dear Lars
I'm restoring a Volvo Penta AQ170A. Running hot after rebuilt.

Background. Boat and Engine stood for twenty years. On startup the Head gasket blew due to corrosion in water ports inside head.
Head now reconditioned and skimmed, new gasket set in, carburettors rebuilt, sea pump rebuilt, motor started first turn.

Out at sea the engine ran fine for about an hour and then suddenly started heating up.

I read two tips on this site and drilled two additional holes in the thermostat as per the advice given, but did so before taking the boat out to sea trials.

I have now after the sea trial Inspected the oil cooler (looks fine), water intake hose, and all the recommended checkpoints, and found the following potential issues:
1. The sea water cross connector is broken. But still turned the seawater pump. It is impossible to turn the pump shaft by hand. Is that normal? I used a jabsco replacement impellor.
2. The hole in the thermostat housing is larger than 8mm, pencil fits into the bottom small hole. what did you use as an insert?
3. I soldered a warm water brass strainer into the riser feeder pipe coming from the exhaust manifold into the thermostat housing. That seems to be working fine and is indeed stopping rust particles. May somewhat restrict water flow as the sive is a fine stainless steel mesh. But I tried without the strainer and the engine still got hot.
4. The thermostat housing is rather pitted inside, must I machine the area where the open thermostat head must "Seal bypass flow"? Please advise.

Seawater here is typically between 15 and 20 degrees Celsius.

How do I attach photos?
Regards
Hugo

Lars Lundbladh
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Blev medlem: 26 jul 2003, 23:46
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Re: solution for cooling problem aq170 b30

Inlägg av Lars Lundbladh » 07 dec 2019, 19:12

hpotgieter skrev:
07 dec 2019, 17:20
1. The sea water cross connector is broken. But still turned the seawater pump. It is impossible to turn the pump shaft by hand. Is that normal? I used a jabsco replacement impellor.
2. The hole in the thermostat housing is larger than 8mm, pencil fits into the bottom small hole. what did you use as an insert?
3. I soldered a warm water brass strainer into the riser feeder pipe coming from the exhaust manifold into the thermostat housing. That seems to be working fine and is indeed stopping rust particles. May somewhat restrict water flow as the sive is a fine stainless steel mesh. But I tried without the strainer and the engine still got hot.
4. The thermostat housing is rather pitted inside, must I machine the area where the open thermostat head must "Seal bypass flow"? Please advise.

How do I attach photos?
I have upgraded you to member so you can see and post pictures.
1. It is not normal that you could rotate the seawater pump by hand. is the impeller cam ok ? (or do you mean the circulation pump?) see picture
0313C57C-22F6-45BF-9A86-EB16F4A23591.jpeg
2. Do you mean hole in the bottom of the cylinder head facing the circulation pump (this should only be restricted if you have a heat exchanger installed.
3. ok
4. I guess not, did you try to run the engine without thermostat and did you check opening temp of the thermostat (boiling water)?


Have you checked the exhaust manifold and riser? If the wall in between the inlet of the manifold = front end is rusted away the engine will overheat this might be the problem?

/Lars
Fjord 900 Dolphin -88 /D6
Ordförande och webmaster i Fjordklubben

turbotuur
Inlägg: 6
Blev medlem: 03 nov 2014, 19:07
Ort: The Netherlands

Re: solution for cooling problem aq170 b30

Inlägg av turbotuur » 07 dec 2019, 21:46

Hi,

I use a 5,5 mm insert in the center hole of the thermostat housing. Experiencing very stAble temperatures since that modification. I used a brass bar and press fitted it.

Of course the rest of the cooling system has to be in good working order. However the center hole determines the bypass flow and tends to corrode and get bigger making the bypass the easy way out for the water instead of trough the engine.

hpotgieter
Inlägg: 2
Blev medlem: 06 dec 2019, 21:24

Re: solution for cooling problem aq170 b30

Inlägg av hpotgieter » 08 dec 2019, 14:17

Thanks for the answers.
Not sure how to reference my own points above.
The pump that's difficult to turn by hand is the raw seawater pump. Same as the one in your picture.
1. I have ordered a seawater pump rebuild kit and an additional cross piece. On receipt thereof, probably only mid January) I will again rebuild the seawater pump and use a new impellor.
2. The thermostat housing:
a) center hole is bigger than 8.5mm. I will leverage your advice and machine a brass rod down then drill a 6mm hole in it and press fit it.
b) the seat around the center hole is also badly corroded away. I assume the thermostat top is meant to close up against this seat when fully open? Thus would close the center hole completely when running fast with more heat. I'm thinking of grinding that seat in the thermostat housing away and machine a seat like a washer around the insert I'll be making for reducing the center hole? Your opinion of doing this?
c) the original thermostat that came with the engine (found in my box of old spares) had a flange around the opening part of the thermostat. It also opened further than the replacement thermostat I bought. Looks like that flange would "cup" around the centre hole seat in the thermostat housing and therefore would Seal the center hole entirely. Ideally we could source thermostat like the original one?
3. Loud sound coming from the universal on AQ 270T when turning the outdrive. Sounds like a dry bearing. I have forced more grease in via the little screw in cap. What's involved here if I need to replace that bearing?

I attach some pictures. Thanks for your help and advice. Really appreciate it.

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