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Discussion Starter · #1 ·
Hello all, hoping to get some input on my latest volvo md7a woes. This is a 1979 MD7A raw water cooled volvo. Here is what is going on and I've tried

When I bought it the flowed almost no water and overheated.

1. pulled exhuast manifold, cleared blocked water passages, flushed out engine with hose.

After this it flowed a good amount of water but temp would creep up and would overheat if I ran it over 1500 rpm for any length of time. Going to lower rpm would bring the temp back down. Water felt cool/luke warm.

2. removed thermostat.

Ran cool, barely moving the temp needle off the peg. Water coming out the exhaust felt warmer

3. put in new thermostat and now it gets hot, just starts to overheat then the temp goes back down to 1/3 (well into the green) then back up etc etc. Sticking my hand in the water coming from the exhaust, it feels like the temp matches what the gauge says (very hot when it's near/just in the red, warm when it goes back down to 1/3)

Did I buy a bad thermostat? I don't have a thermometer to test it but I may have to go buy one. I cleared all the passages in the manifold and water flowed through everything I could find. The transmission leaks water at about 1 drop/ minute, but I don't think that's affecting this. Any experience with thermostats being bad from the factory? Other ideas?
 

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is water getting into your oil

fluctuating temps like that are indicative of a bad head gasket...but eliminate all possible sources before that as a last resort
water pumps good?
 

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Discussion Starter · #3 ·
is water getting into your oil

fluctuating temps like that are indicative of a bad head gasket...but eliminate all possible sources before that as a last resort
water pumps good?
Possible bad head gasket and no thermostat just masked that? There was no fluctuating with the old thermostat, just overheating at over 1500 rpm. Normal cruising is around 2000 rpm for reference.

The oil is dirty, but does not look milky to me.



I've seen oil where the head gasket has really gone and it's obvious, maybe this could be a kind of going but not gone thing? The engine starts easily and makes good power for what that's worth.

Water seems to flow well and the impeller is new this year.
 

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definetely last resort

ok sooo

was your old thermostant oem?

is your new one oem?

thermostats are funky items...sometimes generic and cheap ones work just fine in good motors, sometimes they exhibit your symptoms

if the replacement is original there is a chance its defective,slight but still there

onlt way to check that is to test in hot water and make sure its opening at the temp its supposed to
if its not, or late, or sometimes its defective

get another one

since impeller is new and water flow is good look at thermostat for problems

FOR NOW! jajaja
 

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I know this might seem redundant but are you SURE you completely descaled and cleaned the manifold?, elbows? even hose?
 

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even partially when in gear you can overheat...there are many passages and stuff that you cant get clean the first time

did you clean it in an acid bath or in a shop?
 

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Discussion Starter · #9 ·
I did not do any sort of acid bath, just poked out the passages with a coat hanger. I'm thinking some sort of acid soak might be my next step. I just noticed a thread from about a month ago from a fellow with a MD6a with a similar issue that was resolved using an icemaker descaling solution.

The thermostat is a sierra aftermarket. No idea what the previous one was, it looked the same though. Testing it would make sense but for that to be worthwhile I'll have to get a thermomitor

Mixing elbow is clear, I checked that when the manifold was off.

Oil is supposed to be 20 or 30 weight, I haven't changed it yet.

Thanks for the replies.
 

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yeah change oil and see if you get a smell in the oil quickly, if you do leak somehwere and its thining out your oil

oh I found this:
http://www.bluemoment.com/manuals/Volvo_MD6A_MD7A_Workshop.pdf

and regarding the oil I guess it is just thinner than normal...just make sure it doesnt smell real bad of diesel...

you should be using 20w in temps over 50...straight grade...so get a good quality one...

30 might be a good choice since the engine is old...might help a bit...

cheers
 

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I did not do any sort of acid bath, just poked out the passages with a coat hanger. I'm thinking some sort of acid soak might be my next step. I just noticed a thread from about a month ago from a fellow with a MD6a with a similar issue that was resolved using an icemaker descaling solution.

The thermostat is a sierra aftermarket. No idea what the previous one was, it looked the same though. Testing it would make sense but for that to be worthwhile I'll have to get a thermomitor

Mixing elbow is clear, I checked that when the manifold was off.

Oil is supposed to be 20 or 30 weight, I haven't changed it yet.

Thanks for the replies.
how long, hours since last oil change?:)

do that first that way you can see if yoy are getting fuel into the oil

cheers
 

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Discussion Starter · #13 ·
I don't think it's all that thin. It took me quite awhile to get a halfway decent picture of it, so I think that's contributing to that apperance in the photo. I didn't notice a fuel smell in the oil but I can check again tonight. Straight 20 weight is considered acceptable so for all I know that's what the PO had in there

How would a leak in the fuel pump cause overheating? just by degrading the oil? The oil is really old so fuel leak or no it's probably not doing it's job very well, but I wouldn't expect that to cause this sort of overheating. I was going to wait till I had the cooling issues sorted out before changing it, but now that I have a tstat back in I guess I should go ahead and do it.
 

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Discussion Starter · #14 ·
how long, hours since last oil change?:)

do that first that way you can see if yoy are getting fuel into the oil

cheers
No idea (new to me boat). The fuel filter I took off the engine appears to have been there since 2005... Maybe the oil was last changed then too? In any case, it definitely needs to be done. Didn't think the temp would be very sensitive to oil quality though?
 

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oh yeah it can...one of the first things I ever do on any engine new to me, old or ne is to change fluids asap no matter what the op says...

one of those things...really old oil lubricates and cools less also has sludge....

so it might or might NOT be a factor but an oil change would be the first things I would do, especially since the boat and engine is new to you.

straight grade oils naturally will be thicker feeling than multigrade and are in essence better since there are no viscous changing detergents and the like.

so get a good straightgrade 20 oil and see if it makes any diffrerence...or of it feels different too

thats the first thing id do...that way you start fresh and can see if the oil turns dark real soon, or of it smells soon of fuel etc...
 
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No idea (new to me boat). The fuel filter I took off the engine appears to have been there since 2005... Maybe the oil was last changed then too? In any case, it definitely needs to be done. Didn't think the temp would be very sensitive to oil quality though?
if you are using an engine that has almost 10 year old oil

STOP:)
 
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Discussion Starter · #17 ·
if you are using an engine that has almost 10 year old oil

STOP:)
lol, yes. I did the fuel filters last weekend and was pretty shocked at the date written on the filter (it was either 05 or maybe 09 if the PO was european, though I don't think he was.) Was also shocked that the engine ran at all given their state. I don't think the oil is really that old, but the fuel filter has me pretty suspicious of the PO's maintenance habits. Didn't want to change it till I had a tstat in (couldn't get it up to temp to drain it without one), but will do that asap now that I do have one
 

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yeah man one of those things...start off with know quality and quantity and go from there

ps a cheap thermometer for cooking works great for testing thermostats, and they are cheap...that way you can test it out too

good luck
 

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The thermostat that is in now might be for a Fresh Water cooled engine so it is opening up at 150 degrees or so when a Raw Water thermostat might open at 125 degrees. If you have the box it came in it should say on the box at what degree it will open. The manual should tell you what temp it should run at.
Oh and change the oil and maybe the filter twice! Good Luck.
 

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yup

you have to determine at what temp that thermo opens, only way to do that is to boil it...and see if it does it so correctly and at what temp and repeateadly, you might want to look at getting an oem thermo from volvo penta too...

many a times have I had 2 thermostats for my vehicles one for cold weather and one for hot weather...

anywhoo

good luck

ps. did a bunch of research on volvos last night(im sans an inboard on my boat as the palmer gas inboard died) and there are some sweet running md7a, md11c, md2b 2020,2030 etc out there that gave me some inboard envy for sure!

so take care of yours! jajaja
 
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