Volvo MD11d - thermostat question

[bliss]

this might be a dumb question but here goes - i have some overheating issues with an older Volvo engine which of course could be age related and serious - i have had part of the engine apart and the internals actually don't look too bad so am going to replace the temperature sensor ( i don't think this is the problem but actually the temp seems to fluctuate more than it used to ) and have tested the thermostat by heating in water on the stove and it " pops " ok ... but actually - does the system need a thermostat if I live in pretty temperate climate ( although minimum winter water temp prob 12 degrees C ) - i am thinking of friends with old Landrover 4WDs who run them without thermostats ???

as i said - could be a dumb question but curious

Matthew

[Shawn67]

If the thermostat is working OK then your overheating isn't the thermostat. Is the 11d raw water or fresh water cooled?

My raw water MD7A had very clogged water jackets in its exhaust manifold which was causing the overheating. Prior owner removed the thermostat and I think that actually made the problem worse as the flow balancing was thrown off so most water went through the engine bypass and straight out the exhaust. I had to remove the exhaust manifold and clean it with citric acid, hangers, drill and water pressure to remove all the build up. After doing all that as well as correcting an air leak from the transmission to the water pump the engine runs very cool now. I also converted to fresh water cooling to avoid the build up again.

I'd check your water jackets for build up as well as the brass pipes for old impeller bits. Check your impeller, water pump cover for wear, strainer and if you are fresh water cooled clean out the heat exchanger.

If you do decide to try removing the thermostat you likely have to hollow out the thermostat as you need the ring for the gasket to seal your thermostat housing. If your thermostat is similar to the MD7As you can use a cheap thermostat from a 5 liter Ford Mustang (same flange diameter) as your empty thermostat. If you do this you should also block the engine bypass so that all water is forced through the engine itself. The engine bypass is the water line to the bottom of your thermostat housing.

Shawn

[bliss]

Shawn

thanks for your time - the engine is raw water cooled - in the absence of the thermostat all the water should go through the engine not the bypass shouldn't it ???? I will check out the exhaust manifold though as it is a part of the system i haven't looked into - there was a hot water service on the boat ( divert of heated engine water through a central heat exchanger in a stainless steel drum ) and i had ended up with a convoluted plumbing arrangement after removing that - i have rectified that and i think there is an increased amount of water being pumped out the back of the boat than before - but is still overheating - just taking longer .... looking at the amount of exhaust water though i think it probably isn't a problem in the exhaust manifold but will check it out

Matthew

[DougR]

As described by Shawn67, the thermostat controls water flow in the cooling system. Water flow from the seawater pump travels to the "t" on the bottom of the exhaust manifold where it splits, either flowing thru the engine, or flowing to the bypass side of the thermostat housing and then to the exhaust.

When the engine is cold the thermostat is closed, stopping flow within the engine and forcing all flow thru the bypass passage in the thermostat housing.
As the engine begins to warm up, the thermostat starts to open, allowing some flow thru the engine and some thru the bypass passage. If there are restrictions within the engine passages, most of the flow will still go thru the bypass.
When the engine gets hot the thermostat will fully open allowing maximum flow thru the engine. Besides being fully open to flow, the block-off plate on the thermostat will also move toward the bypass passage in the thermostat cover and block the bypass opening, further forcing flow thru the engine.

If you remove the thermostat, you will no longer have a block off plate to close off the bypass passage in the thermostat housing, and water can continuously bypass the engine. This will virtually guarantee an overheating engine.
Bottom line....the engine needs a thermostat with a block-off plate to function properly.
DougR

[Dartanyon]

I have the exact same engine, and had the exact same problems. Previous posters are correct. Removing the thermostat gives the appearance of the problem being fixed, ie the temp gauge reports cooler, but the cylinders get hotter, doing more damage. It's the water galleries around the cylinders that are clogged. I bought a cheap pump and a bucket and back flushed CLR through the cooling system. About and hour at 100% solution, then 8 1 hour flushes with clean water. This alleviates the problem, a bit. My guess is that at the end of the summer I'll have to remove the exhaust manifold (don't forget to have new gaskets on hand) and manually clear the galleries out further. But for now I just got back from having to run the engine for 7 hours, with no issues.

[tbosch]

I have a Volvo MD17c, which I think is similar to yours. Mine is also raw water cooled and was having an overheating problem. My problem was in the thermostat housing. I removed it and saw that one of the channels through the housing was completely clogged with mineral deposits. Cleaning and reinstalling corrected my overheating problems. It might be worth checking on yours.

Todd

[MarkSF]

Removing the thermostat is the recourse of incompetent mechanics the world over, to cure overheating. It, of course, doesn't work - although it does ensure long warm up times, with consequent waste of fuel, before the overheating starts!

"i am thinking of friends with old Landrover 4WDs who run them without thermostats". They don't know what they're doing either.

The solution to overheating, presuming that everything is working as it should, is to INCREASE the cooling capacity of the system. Amazing, eh? A larger radiator, larger fan, or in the case of a boat, larger heat exchanger. (larger in terms of heat transfer, not necessarily physically).

[garyj4101]

Temperature sensor and thermostat are two separate entities.
Sensor measures the temperature within the engine block and sends the data to a temperature gauge.
Thermostat controls the water flow within the engine block by restricting flow until correct operating temperature is reached and maintaining constant temperature. Just because a thermostat opens when testing on a bench with hot water does not guarantee it's operating at the correct specs. The cost of a new thermostat is negligent (a few dollars) compared to the damage that can be done by not operating the engine at the temperature it was designed for, not to mentioned increased fuel consumption, etc.

Gary

[Shawn67]

“- in the absence of the thermostat all the water should go through the engine not the bypass shouldn't it ???”

No, it will follow the path of least resistance which is the engine bypass. The thermostat sort of closes off the bypass as it opens forcing water through the engine.

“ I will check out the exhaust manifold though as it is a part of the system i haven't looked into “

In my case the ports from the exhaust manifold that flow water into the block were completely clogged shut, not flowing at all. All water was going through the bypass. Even the inlet on the bottom of the manifold was completely clogged shut to the point that I thought the brass tube had been JB welded in place. It was only after soaking it in strong citric acid for days that I was able to get that freed up.

“ i have rectified that and i think there is an increased amount of water being pumped out the back of the boat than before .. looking at the amount of exhaust water though i think it probably isn't a problem in the exhaust manifold but will check it out “

If your flow is similar to the MD7A (and I think it is) from your water pump the water takes two paths. One is the engine bypass that goes to the thermostat housing and straight out the exhaust. The other is into the exhaust manifold, through the engine, through a small bypass in the exhaust manifold (so some water cools it even when the thermostat is closed) and a small thermostat bypass to get heated water to the thermostat to open it.

Your exhaust manifold could be completely clogged and not flowing, stopping all flow into the engine, yet you would still be seeing water in the exhaust due to the engine bypass. Get a $20 IR temp gauge and measure your exhaust manifold. If it is above about 140 degrees it is too hot and is the first entry point for cooling water into the engine. It is also where the volvos commonly clog up due to the heat of the exhaust pulling salt out of the raw water.


Shawn

[Saltyrope]

Hi Matthew, I have owned and worked on these engines with a similar problem. Some of the answers have addressed some of the problems. before coming to the most important issue I agree with the cleaning out with CLR or similar. Salt Away and various products can be used. An 'acid wash' was a term used in some trades previously. A soaking of all the internals for several days may be needed to shift some of the more dense build up. The solution must not back flood through the exhaust pipe and my suggestion is that you remove the water injected exhaust bend and thoroughly clean it out using mechanical and chemical means. These do block up and can also suffer from internal cracking. See. https://www.marinepartseurope.com/en...-26-15108.aspx
With the water injection hose lifted to a level to allow the CLR or similar fill all the cavities the water chambers can be left soaking. An initial week or so of soaking, after which a good run with normal cooling water will usually give a lot of 'crud' coming out the exhaust.

However to the often crux of the matter. Bearing in mind that some small cavities may be almost impossible to clear without mechanical means it can only be hoped that they are porous enough in the build up to gradually clear.

As mentioned, the crux of the matter has been in some cases the actual thermostat itself. The temperature of thermostats in these engines start to open (from memory) at 58 degrees Celsius. Putting in a regualr automotive thermostat opening at even 80 degrees Celsius would encourage deposits.

After a certain temperature of heating, salt water 'drops' the salt out of the water and it deposits itself on the heated surfaces of the internal chambers in the engine. When testing the thermostat it must start to open at the low temperature or it is faulty.

When replacing these particular thermostats with the genuine part, I would always drill a one eighth hole in the opening cap plate. That assisted in eliminating air bubbles but more importantly allowed a very small flow of water to gradually equalize the water temperature each side of the thermostat cap and encouraged a small water flow so through the chamber which helped relieve a sharp transition from cool to hot as the thermostat started to open.

As a side benefit, if the thermostat failed to open through a fault, which these thermostats did seem to suffer from after some time, the small one eighth hole ameliorated the effects of a jammed thermostat.

To pump through the CLR or similar, removal of the water inlet hose after shutting off the seacock and putting that inlet hose in to a bucket of the de-clogging mixture will take it through the engine chambers. After the initial flush through the whole system, when it is observed that the solution is coming out the exhaust pipe there is the option of removing the hose that injects water into the exhaust elbow and equalizing the height of the inlet hose and that exhaust water injection hose so each may be topped up until full, above the engine water chambers.

There may be air pockets, bits or impeller vanes and suchlike in the system so it is a matter of checking each part out, including de-laminating hoses and I have probably overlooked other possible issues here. For actual cleaning of systems I have sometimes chosen to take the thermostat out just to allow a less obstructed flow of the cleaning solution. Most important is the genuine low temperature opening thermostat and my personal modification of the one eight hole to assist with future temperature transition. Checking the impeller and the impeller cam may be worth while of course. If I have made any errors in the above or omitted anything , then others may be able to improve on suggestions. All the best. Regards, John

[Roeschaert]

You never know :
Did you check the van of the incoming seawater , mine had a copper filter
which was blocked from oxidation .

[GordMay]

Greetings and welcome aboard the CF, Todd, & Roeschaert.

[bliss]

thanks for everybody's help/time - love this forum for getting answers to questions