Universal 25 Overheating and Diesel leaking

[Leonitas911]

I’ve had issues recently with my Universal M25 overheating after 5-10 minutes of run time. I’ve replaced the thermostat, coolant pump, impeller and a few of the hoses and verified the heat exchanger isn’t clogged. I bled the air out and made sure the coolant was flowing thru the thermostat housing yet the engine still overheats after 10 minutes or so. It seems like thermostat isn’t opening at the proper temperature or the coolant isn’t circulating through the heat exchanger for some reason. Please help me and give me ideas to check anything I haven’t thought of already.

Also, while working on all of those repairs I noticed a diesel leak that appears to be coming from the high pressure fuel line, not where it connects to the injector but from the other side (what I assume is the fuel pump but I’m not 100% certain, I circled the area I’m referring to in the attached picture).

The engine sounds good while running so I don’t believe it’s causing any air bubbles but I still need to fix it. I’ve tried to search for replacement parts but haven’t found anything. Can anyone recommend the proper parts or maybe an upgrade over the old metal lines?

Thank you!

 

[WayneH]

One more troubleshooting tip on the overheating. Did you verify the coolant temperature with a remote thermometer? Cuz just maybe the temperature probe has failed. Lower coolant hoses are not collapsing while the engine is running? If those items check out, it sounds like you may have problems with the engine coolant jacket.

I'm going to catch flack for suggesting this but I fixed my problem by running a 50/50 mix of CLR and water through the engine for 15 minutes with the thermostat removed. Drain this mixture and run straight water for another 15 minutes then repeat the clean water flush. After that, refill with coolant and reinstall the thermostat. Like I said, it fixed my problem. YMMV

Air bubbles only come in between the tank and the lift pump which is the area under vacuum. After that, all leaks are out of the pipe. Tightening the nut with a wrench and getting a tiny bit of movement may fix the leak here. However, I always worry about breaking something when attempting to tighten an already tight fitting.

You might ask a diesel shop if they can duplicate the line. Show them the picture first and then bring in the part if they say yes.

Hopefully, someone will add to these suggestions with FACTS.

 

[Stu Jackson]

Additional thoughts:

1. You have the old alternator bracket. it is a disaster waiting to happen. Classic M25 issue.

2. Your hoses need to be replaced. Could well be blockage there somewhere.

3. More engine info read the Critical Upgrades topic info in the links below, too.

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too This includes a link to the Critical Upgrades topic which has more engine information please read it too.

Diesel Engine - c34.org

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There is a lot of other good engine and general boat info here:

"101" Series - Quick Links to "Popular" Topics includes "Electrical Systems 101"

 

[TimFromLI]

I assume you are getting good water flow out of the exhaust. I had the same engine, the cover plate for the raw water impeller can get grooves which prevents the pump from priming. I sanded out the grooves - problem solved. Also, use the right gasket, too thick will cause the same problem.

 

[TimFromLI]

Thee are aftermarket fuel lines with fittings available on amazon which might work if all else fails- or try ebay for used parts

 

[sailme88]

I too have an M25. HAD overheating issues. At one point it was the raw water pump. The fix was replacing the pump...Next season started to note a slow rise in the operating temp. Tried a myriad of fixes..Finally decided to get a laser temperature gun. When the cockpit gauge was indicating 200 degrees the heat gun was saying 165. Bought a new gauge.. nope.. I deeded to get a gauge with sending unit.... now all is well...

 

[jibes138]

A couple things you can try.
Heat the thermostat in hot water, make sure it opens at 160 or so. You can use a cooking thermometer for the water temp.
Pull the hose off the water injection to the exhaust stick it in a bucket, start the motor and verify good flow.
Run it with no thermostat. The thermostat works to modulate the temp at an equilibrium value. Without it the motor should run cold. If it still overheats you either aren’t pumping coolant or raw water is restricted.
If you have original 2” HX get a 3 inch. Check you HX for zinc debris in the raw water outlet. This accumulates over time and no end cap on that end to clean it out. Fish out debris through the outlet fitting and port for the zinc. This loose stuff can move around and restrict flow, cleaning the HX tubes doesn’t get it out.

 

[jibes138]

Not to offend but make sure the raw water sea cock (or valve if not a sea cock) is open.

 

[jssailem]

Thehigh pressure fuel lines on your enigne look like steel fuel lines. This type of line cna be flared or straight with copper compression ferrels that fit over the line. The ferrel compresses providing a sealed fit. These are a one time use item. New ferrels should be used each time they are released. You will need to release the nut and lift the fuel line carefully. clean out the rim of the pump outlet with a clean cloth. Be sure not to let anything contaminate this area. Slip off the old and slip on the new ferrel then tighten the nut. Tension firm but not "crushing".

The other type of fitting found cn be a flared end fitting. In this cace the flared end sits in the pocket on the pump. Check to see thqat there is nothing (i.e. dirt, rust, grime) stopping the fared end from fitting snuggly. Clean and reseat the fuel line.

When finished presurize the fuel. plead the air if needed, then check that the leak is gone.
Good luck.