Volvo MD7B running hot in the summer in Texas

[reenacub]

My Volvo MD7B runs hot when the water heats up in the summertime in Texas (very hot right now). My temperature guage only has green and red, no numbers, so I don't know exactly what the temperature is, but it will come up to the red and usually stop right there as long as I keep the rpm's down. It has gone up into the red a little bit, but not too much.

It has a 180 degree thermostat on it and when its running cool, you can see the thermostat open and close on the temperature guage. At that point, the needle on the guage is about 1/4 inch from the red zone. So I'm guessing that the red zone probably starts at about 200 degress. I run 50/50 water/coolant mix.

It has a Sen-dure fresh water cooling kit on it. Its a 1983 boat and engine and I bought it in 1993 and it had the fresh water cooling on it when I bought it. As far as I know, it has always had the fresh water cooling system on it.

This has been an ongoing problem and I have been through the cooling system multiple times. I even had it "de-scaled" (flushed for 5 hours with rid-lime).

The accumulation tank and the heat exchanger get hot to the touch. Both pumps have been serviced and are working good. It has good raw water flow through the exhaust.

Having not been able to find anything wrong, I am wondering if the heat exchanger is too small. This heat exchanger is for an MD7A engine. Sen-dure doesn't have one for the MD7B. The MD7B is a 17hp engine vs. 13hp for the MD7A. They both have the same block but the MD7B achieves more horsepower through higher rpms (3000). However, I don't run it that high. I keep the revs down in the summer.

If anyone has any experience or insight on this, I would appreciate your suggestions.

Thanks,
reenacub

[Shawn67]

" My temperature guage only has green and red, no numbers, so I don't know exactly what the temperature is, but it will come up to the red and usually stop right there as long as I keep the rpm's down."

If your engine was originally raw water cooled and it still has the factory temp. gauge you might want to start there. My MD7A gauge (no numbers, just green and red) was reading into the red at about 140 degrees. I ended up swapping the gauge and sender to get better info.

Get an IR thermometer ($30ish at Home Depot) and check the temperature of your exhaust manifold, head and block with it. That will give you a good idea on what the engine temp is really like.

I converted my MD7A to fresh water cooling this season and part of that was removing the exhaust manifold and clearing out all its water passages. Even with 170 degree thermostat I don't really get that hot due to the various bypasses in the MD7As cooling system. Exhaust manifold is typically around 130 degrees and the block is around 150-160. That is cruising at 1600-1800 rpm.

Shawn

[reenacub]

Thanks for the reply.

What kind of temperature guage and sender did you get? I would like to have one with numbers on it.

What kind of fresh water cooling did you put on yours?

The IR thermometer is a good idea. I will get one.

I can't imagine that the galleries are plugged up. Its always been fresh water cooled and was de-scaled, but I guess anything is possible. I'll get the IR thermometer and take it from there.

Thanks for your help.

[Shawn67]

"What kind of temperature guage and sender did you get? "

Stewart Warner 82114 with a 280EA sender.



The sender comes with adapters to fit different size openings. I have two MD7A exhaust manifolds and the sender hole is different between the two.

I designed my fresh water conversion. It is a Sen-Dur 2550 heat exchanger from a Yanmar 2QM20. I used a Johnson piggyback pump on top of the existing raw water pump on the back of the engine. Original raw water pump became fresh water and new pump became raw water.

"I can't imagine that the galleries are plugged up."

The feed from the exhaust manifold into the head (which in turn feeds the block) is relatively small so something could get in there. An old impeller blade for example. In my case the exhaust manifold was completely clogged and not flowing water at all. But mine had been raw water cooled and was filled with gunk.

"and was de-scaled"

Did you block the engine bypass and remove the thermostat when you de-scaled it? If you didn't you may not have been flowing much through the engine itself. No way mine was going to clean up by just de-scaling it. I had to get in there and physically clean it out.

But you might not be overheating at all. Getting more info with the IR thermostat will help.

Shawn

[reenacub]

Thanks again for the good information.

I'll start with the IR thermometer. Will look into the temp guage.

If you want to part with one of those manifolds, I might know someone that needs it. Theirs is rusted out. Don't know if they found one yet. Volvo price was $1650 !!!!!

Sail well.

[Mplight]

Hello,
We have a 1984 Barberis Show 30 with MD7B, which we purchased 18 months ago. last month on an overnighter to Cutty Hunk off the South east MA coast, engine overheated and black smoke filled our cabin, shut off engine and sailed the rest of the weekend- fair winds in our favor!
the issue was the impeller failed and melted the hose connection of the Waterlock, and after further inspection determined the waterlock box was also melted on the bulkhead side- unseen until removal!
replaced impeller and tried to inspect the Thermostat- which unfortunately was missing (my bad for not knowing)- however, it was filled with a lot of corrosion- Raw (salt) water cooled.
I cleaned out the Thermostat cover and hookups- the new thermostat is rated for 160 degrees! and its been suggested that I go to 140 degree.
In any case, new Impeller, New Thermostat, new Waterlock and hoses,
engine runs better quieter and a lot cooler. hope this helps good luck.

[Shawn67]

"which unfortunately was missing (my bad for not knowing)- however, it was filled with a lot of corrosion- Raw (salt) water cooled. "

Not having a thermostat tends to make the engine actually run hotter as it lets the engine bypass flow freely instead of forcing some coolant through the block. My engine didn't have a thermostat when I bought it too. If you have to run without a thermostat in an emergency you should restrict the flow through the bypass (brass hose to bottom of thermostat housing) to force coolant through the engine.

" the new thermostat is rated for 160 degrees! and its been suggested that I go to 140 degree."

Being raw water cooled 160 degrees is too hot, switch it to the 140 which is what it came with from the factory. Salt precipitates out of saltwater around 160 degrees and that will clog up your cooling passages.

Shawn

[Jan Rydstrom]

Hi! I used to have an MD7A equipped with an effective Martec fresh water cooling system. Martec is a a Swedish system I think, at least it is sold under that name here but I don't know if it is available in the US. My engine, approx. the same age as yours, overheated, so I cleaned it a couple of times with a car cooler cleanse to remove iron oxide deposites which worked very well. Temperature still got close to the red but never much more. Interestingly, the temperature actually fell somewhat with increasing rpm.In your case the exchanger might indeed be too small (but I would try the cooler cleanse first). One alternative to replacing it is to install a cabin heater run by the hot fresh water system of the engine. This is an easy thing to add, and it should also have its own circulation pump. Here in Scandinavia such a heater is wonderful when it gets chilly, it always keeps the boat warm and dry. In Texas you might also consider that, despite your much higher warmer climate, a dry boat is always nice to have. The temperature of the engine drops by some 10-15 degrees Celsius, enough to always keep the meter in the green. Jan

[Don C L]

A friend of mine just got a boat with an MD7A and it had overheating issues but his does not have a heat exchanger. We pulled the engine out (not as hard as we thought) and his mechanic friend went through the whole block and head cleaning out the years (not hours, it had low hours) of (raw water cooled) black gunk, sometimes with a drill. When done with that he then put it back together and ran the acid bath through it and more black goo came out. We haven't put the engine back in yet but we are hoping for the best. I did read on a thread here once that the raw water should never go over 145 or it starts to cause the build up, but that seems a little cool for the engine. I hate to say it but you may need to do a similar more labor intensive internal cleaning. There may be one little chunk of gunk or impeller plugging things up that the cleaning flush can't dislodge.

[Shawn67]

Yup, the exhaust manifold can gunk up pretty badly. Removing the manifold is fairly easy though and lets you really clean it out well. Did the same thing on my MD7A and now it cools very well.

"I did read on a thread here once that the raw water should never go over 145 or it starts to cause the build up, but that seems a little cool for the engine. "

Factory thermostat is 60 degree celsius which is 140 degrees. Raw water cooled engines have to run cool if they are used in salt water.

Shawn

[barnakiel]

Higher hp of your engine may play a role. You will know this if the engine does NOT overheat at lower revs.

Coolant mix plays a role too. I have heard that less glyco / more water cools better than the opposite option. (e.g. Things you should know about coolant | hellafunctional)

Cheers,
b.

[hpeer]

For salt water cold MD7 there are a number of things that can cause it to run hot. I think I have found them all at one time or another.

I'm presuming the fresh water uses the normal sea water pump?

The lines from the trqnsmission to the pump and the in and out connections to the pump can be flakey.

If your issue is consistent you are likely on the right track. If intermittent, then there may be other issues.

[hpeer]

For salt water cooled MD7 there are a number of things that can cause it to run hot. I think I have found them all at one time or another.

I'm presuming the fresh water uses the normal sea water pump?

The lines from the transmission to the pump and the in and out connections to the pump can be flakey.

If your issue is consistent you are likely on the right track. If intermittent, then there may be other issues.

[Lepke]

Put a real gauge in so you know the temp. It could be you are running in salt water that is too warm to properly cool the fresh water with the heat exchanger you have.
However both water systems need descaling. Before I bought a bigger heat exchanger, I would disassemble the water systems and closely inspect. Also, I wouldn't "have it descaled", I would do it myself. Then you know.
I use Rydlyme in the fresh and salt sides and it has never failed. My heat exchangers look new. (You have to remove any zincs when using).
http://www.apexengineeringproducts.com/ Available on Amazon & Ebay.
If you have excessive rust Archoil AR5100 eats thru flake rust to the good metal. It doesn't dissolve good metal, paint or coatings. It also works on heat exchangers, too. Archoil | The Latest Developments In Nano lubrication

[SF Bay Dude]

Originally Posted by Lepke

Put a real gauge in so you know the temp. It could be you are running in salt water that is too warm to properly cool the fresh water with the heat exchanger you have.
However both water systems need descaling. Before I bought a bigger heat exchanger, I would disassemble the water systems and closely inspect. Also, I wouldn't "have it descaled", I would do it myself. Then you know.
I use Rydlyme in the fresh and salt sides and it has never failed. My heat exchangers look new. (You have to remove any zincs when using).
http://www.apexengineeringproducts.com/ Available on Amazon & Ebay.
If you have excessive rust Archoil AR5100 eats thru flake rust to the good metal. It doesn't dissolve good metal, paint or coatings. It also works on heat exchangers, too. Archoil | The Latest Developments In Nano lubrication

Lepke, when you use Rydlime, how do you circulate it through your system?