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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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  #1  
Old 09-17-2009
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Access to Volvo MD7A Thermostat

I'd like to remove and test the thermostat and flush the cooling system. However, when I remove the two bolts off the cover, a metal cooling line attached to the bottom rear of the cover prevents the cover from being removed. Attached are photos of the cover and the pipe that exists the rear. Any thoughts on how to deal with this and get the cover off withought breaking something? Thanks in advance.
harbin2
Islander 30 Bahama, 1981
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Access to Volvo MD7A Thermostat-cover-front.jpg   Access to Volvo MD7A Thermostat-cover-back.jpg  
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Old 09-18-2009
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One thing that is easy to overlook is the cam that deflects the rubber impeller is prone to significant wear but is easily replaceable, it is secured by a small screw on the outside of the body. My experience is
confined to of a raw water cooled MD2B but presumably your(s) has the same facility. When I eventually saved enough funds for the gaskets to strip the top end It took me a day to clean the crud out of the waterways (I also found the source of the oil fumes was a missing bolt between the barrels. I took the old thermostat to an auto shop and managed to find a replacement with the same temperature setting.... Thanks for sharing the post....
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Old 09-18-2009
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I had a MD7A on my first yacht. I plumbed a 'tap' at the water intake and in the marina I flushed the engine with fresh water by connecting a hose.
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Old 09-18-2009
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I'm not familiar with the MD7A so take this with a grain of salt. The Volvos I have use similar looking tubes in the cooling system and they have O-ring type seals on the ends. The bolts hold the tubes under compression. I would call your local Volvo dealer and talk to the shop foreman, he should be able to explain what you have there. I'm guessing that some PB Blaster up in where the tube goes into the thermostat housing will allow it to come apart, but check with Volvo.
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Old 09-24-2009
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I have had significant experience with this motor, and this joint.

The end of the tube seats into the housing with a SPECIAL oring seal. They used square cross section o rings.

Go to the Volvo site, they have all the manuals, shop and parts, that can be downloaded.

loosen the bolts, and tap around the housing to free i tup from the bolt faces. Leave the bolts in place, just loosen them. Get the housing free floating with the bolts in place.

Then tap the housing away from the tube, slowly, take it easy. use wooden or brass drifts or blocks. it will break free, but by leaving the bolts in and just loose, you prevent the housing from cocking and bending the end of the tube. if you bend the housing down and away to break it free from the tube, you'll damage the tube and it wont seal again.

Prior to removing, lube the joint over a couple of days with a silicone lubricant, not an aggresive penetrating oil. The seal will swell, making the job worse.

anyone with these motors needs to know that there are tiny water passages in the coolant jackets, and if those plug your engine will be trash. these engines must be flushed with a chemical flush to clean those passages, and should be flushed several times during the process.

The best day of my boating life was the day I tore that md7a down, and tossed it over the side onto the ground. This engine should not be rebuilt. I rebuilt mine, and it was a waste of 3500 bucks. it lasted 2 seasons after rebuild.


"Volvo Green makes me Mean!"
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Old 09-24-2009
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Jeff - thanks for the advice but sorry to get you fired up. I have the same type joints on my raw water pump but those have metal rings around the lines that appear to be the type of hose clamp you release with a pair of plyers. I can't figure out what purpose they serve - see below (sorry about the green). Since my original post just a couple weeks ago, I have identified a leak on the raw water pump seal that is dripping about 20 drops per minute out of the weep hole in the bottom of the pump - between the two seals. So I now also need to take the water pump out and disconnect those joints. I assume they are also the same "o-ring type as the thermostat housing. Agree? Are the o-rings typically damaged when removing the tubing?

Correction - looked at the back side of the pump today and realized that the metal rings on the inlet and outlet of the pump are connected together. Apparently they are meant to keep the lines from popping out of the pump - odd design (to me).
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Access to Volvo MD7A Thermostat-raw-water-pump-inlet.jpg  

Last edited by harbin2; 09-25-2009 at 10:46 PM. Reason: Correction
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Old 12-13-2009
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Jeff - and others.
Thanks again. I got the thermostat housing off a couple weeks ago. As you suggested, I left the two bolts in place and wiggled, pryed the housing off so as not to let it get cocked on the pipe. It did come off - with some patience. I was glad I got it off. What a mess inside. Lots of corrosion and crud all over the inside of the housing, thermostat, and passages. I cleaned everything out the best I could and am developing a flush plan for the spring. First I'll forward flush, then back flush. I think I was able to figure out the flowpath through the engine and the bypass around the thermostat to keep the water pump "lubricated". I hope to visit my Volvo dealer in the next few weeks and will ask him about the O rings with the square cross section. I'll also ask him for recommendations on a flush but I may try a couple "non chemical" passes first.

My next project will be to remove the raw water pump since the pump's shaft seals are leaking a little. I assume the inlets and outlets have the same O rings.

Thanks again,
Ron

Last edited by harbin2; 12-13-2009 at 03:42 PM. Reason: Ommission
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Old 12-13-2009
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now you've other issues.......

You see the corrosion. You're going to flush. And you might end up ruining the motor.

Know this....there are very small cooling passages around the cylinders and to the head.

If you start flushing, keep flushing, and keep flushing, and keep flushing. But you can't use a real strong cleaning agent, as it will attack the orings.

This is what happened to my MD7A. Cleaned it up after 20 years of not being flushed, it loosend the corosion, then the crud went to the smallest cooling passages, and caused the engine to overheat around the cylinders, causing the rings to take a set, loss of compression resulted. And the temp gage did NOT show the localized heating problem around the cylinders.

Then you'll want to rebuild, and throw more money into a great, but old, motor.

Then a $3500 overhaul, then 2 seasons later the new seals may have gone bad, filling the crank with water, ruining the engine. Thats what happened to mine.

key is being sure the engine is really flushed, and all the passages are clear.

And I don't have a clue how you can do that.

Good luck!
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Old 12-13-2009
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O rings - cheating

I was able to cheat a number of time on orings for the md7a. $5.00 or more at the marina, vs $0.23 at a real hardware store that had real selections.

o rings vs the square rings, just had to use soft compound and larger diameters
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Old 12-14-2009
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Thanks for the additional tips. I'll be very skeptical about a chemical flush and will be careful about non chemical flushing. With the clogging I could see in the larger passages, I can imagine what things look like in the smaller ones. And I can see how loosening the crud that's there will cause potential problem. Also, when I finally got the thermostat housing off, I didn't even look inside the passage where the copper pipe (inlet) inserts. There is a raised ring about 3/4" from the end of the pipe (expanded from the pipe itself). At the time, I thought this created the seal. After re-reading your post, I now realize that there is a rubber O ring that must be stuck in the hole. When I remove the housing again in the spring, I'll be ready with one or two square o rings and a handful of the hardware store variety.

I'm a little concerned that I may be doing too much (if it ain't broke, don't fix it). The boat is still relatively new to me (one season old). For most of the season, the temperature gauge stayed in one spot - at about 1/4 on the scale at the lower end of the green band. On several long (4 or 5 hour runs) in the heat of the summer (air and water temperature), the engine gauge would climb almost into the red at only about 2400 rpm. Reducing the RPMs made it cool off. Of course, as you point out, the temperature on the gauge is average and not local around the cylinders. That made me nervous and is why I'm planning on the flush.

I have spoken with the original owner and he took much better care of the engine than the next two owners. So I'm trying to recover from some unintended lack of preventive maintenance.
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