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AQ130c Overheating at higher rpm

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uno759

Contributing Member
"I have 2 AQ130c,s one of whic

"I have 2 AQ130c,s one of which is over heating when i go over about 2,800 rpm. This problem seems to getting worse as it only used to over heat above 4,000 before. I have disconected the the sea water filter and given it a good clean and have blown down the pipe that goes to the leg to see if it is blocked but its all clear. This weekend i changed the impeller just incase something was wrong there but having tested it there is no difference it still overheats. Interestingly it does,nt overheat if I run at anything under the 2,800 its just when I go higher and if i go higher then lower the rpm back below 2,800 it does come back down but very slowly. Any ideas what should be my next step ? O and I have checked the drive belt to ensure the tension is correct in case it was slipping causing the impeller not work!"
 
"Have you cleaned out the oil

"Have you cleaned out the oil cooler? Run a rod through the ports in the cooler, it doesn't cost anything. Although it should overhead at low rpms if clogged.

Sometimes the brass (or whatever material) plate that the impeller rides against can get scored and allow a loss of pressure. On some pumps you can turn this face plate around."
 
"Hey El,
would it be safe to

"Hey El,
would it be safe to say that the temp of the coolant directly reflects the temp of the engine?"
 
"Jason,

Indeed, the coolin

"Jason,

Indeed, the cooling water temperature does normally reflect the engine temperature, but there are exceptions. For example, if you have a heavily scaled block in a raw water cooled engine (say an AQ130) the heat transfer between engine and water will be more difficult than in the case of a clean block, in which case the water temperature will not reflect the real temeperature of the engine."
 
"El,
I have a AQ131d which I

"El,
I have a AQ131d which I don't belive is raw water cooled. I asked the question because the engine was running hot according to the temp gauge but I first wanted to check the coolant temp to see if it matched up with the temp gauge and it did not. The coolant measures 190 and the temp gauge reads 250+. I don't think it's running hot but now need to trouble shoot.
Any info would be great. Thanks EL."
 
"Jason, it seems that either y

"Jason, it seems that either your temperature sender or gauge could be wrong. If you check the block temperature with an infrared thermometer, its reading should be very close to what the temperature gauge indicates. In any case, I suggest that if the coolant temperature was really 250ºF+, the coolant would be boiling and pouring out of the tank."
 
"El,
I thought it was the te

"El,
I thought it was the temp sending unit so I ordered and installed a new one but it didn't lower the temp reading. I'm thinking of ordering a new gauge but I'm looking for a "work-around" just to get a more accurate reading. (maybe a mechanical temp gauge- but if so, how to rig it in the engine block?) Mostly concerned about doing damage to the engine if temp is too hot.
Thanks."
 
"There is nothing wrong with a

"There is nothing wrong with a conventional electric gauge + sender, they are relatively inexpensive and many outlast the boat in duration. What I normally carry onboard as well is a laser thermometer to verify gauge readings and to pinpoint any source of heat.

I forgot to ask you to verify that the wire going from the temperature gauge to the sender is not grounded anywhere, either totally or partially. To verify this, just disconnect it when the engine is warmed up and it should drop to zero; if it doesn't then there is a ground somewhere. I just had that problem recently, as the wire was touching a hot spot in the middle of the intake manifold (Chevy 350) and the insulation melted, causing a ground and the temperature reading going through the roof."
 
"El,
Thanks for all the good

"El,
Thanks for all the good info. I'll check to see if the wire is grounded somewhere and I guess I'll look into getting a laser thermometer for my own peace of mind.
Thanks again."
 
"I really kicked summit off he

"I really kicked summit off here then ? threads within threads ! Back in overheating world of Uno759, I did as suggested and checked the thermostat. I actualy removed both from each engine to see that the one (Port side, no overheating probs)was in a right state, corroded and had lost its centre holding bracket assembly. But this one works fine with no issues. When I removed the other (starboard side, the one overheating) it was in a better condition but had the holding assembly inside in tact also i noticed that the port side thermostat has a very small hole in the top whereas the starboard side had no hole. Im yet to run both engines up again to see what happens but I did swap the thermostats over to see if this overheating problem will now be seen in the other engine. I also had a chat with an old sea dog (think his name was Neptune ???), well in truth he had a chat with me, I just knodded like the village idiot pretending I understood what he was talking about. He spent a few minutes looking at both my engines, shook his head in a disapproving fashion and told (more like instructed !) me that I should drill a 4mm hole in the top of each thermostat to ensure a continual flow and erradicate any air bubbles that develop in the system.

He also said I should think about running the small pipe that presently goes to the air filters and silencer (top of the carbs) straight out of the boat to deal with any back pressure issues.

Finally he muttered under his breath "Solex O'dear" and as he walked away then he looked back and said get yourself sorted with a stormburgh ! at least thats what I think he said ? If I ever need his advice again i can simply follow the trail of seaweed and barnicles he left along the jetty as he left. Having said all that Ide greatly appreciate your comments as to both what I have done and also if there,s any merit in what "father time" had to say about the holes in the thermostats and dealing with back pressure (i thought that was wind personally) ? Look forward to any comments.

Lucky for me he did'nt know that when I got the boat in August I did'nt even know where the spark plugs where let alone change carbs, check out thermostats, replace impellers, clean filters, look for perished pipes, change alternators and the list is endless but all because I have learnt from this forum and im prepared to listen to some of the more experienced people here. Keep up the good work."
 
"Uno759, the small hole in the

"Uno759, the small hole in the thermostat is to vent any air that my be trapped in the system. Some thermostats have the hole and some don't, but you can drill one (2 to 4 mm) if you wish as good ol' "Neptune" suggested. In my opinion, it is safer to have the hole in the thermostat.

However, I disagree with running the crankcase vent overboard, as in addition of increasing pollution you will increase your chances of getting moisture inside the engine. There is always a bit of blow-by gas coming through that vent and it is safe to return it to the carburators' flame arrestors, but if the blow-by is excessive this is an indication that your engine is tired (gas passing through piston rings and reaching the crankcase) and needs to be rebuilt.

Regarding Zenith Stromberg carbs, I don't think they are more reliable than Solex, it is just a matter of preference; like in the V-8 engines (Fords and Chevs), some people swear by Holleys (like me in my particular application) while other people are advocates of Rochesters. If you have an engine with good compression, which is well timed (ignition and valves) and the carb is in good condition and well adjusted, etc I doubt you will notice much of a difference either in fuel economy or in performance whether you use Zenith Stromberg or Solex carbs. The trick is to keep your current power package in top condition."
 
"Thanx for the all the feed ba

"Thanx for the all the feed back El, today we lifted the boat out of the water to start a week of maintainence and especialy to refit the new exhaust elbows ive been on about changing for the last few months. Ive decided to go the "take manifolds off route" after all the advice ive been given so all things being equal i can sort the exhaust out then drill a hole in the thermostat thats not got one yet and sort a few other minor problems out like rigid steering gear, retaining pawl not working, reset the gear shift in the starboard leg just to mention a few. This should keep me quiet for a week then ile report back my progress and any remaining issues under another heading before this thread becomes an epic novel not relevant to the original heading. Thank you once again for all the help."
 
"Good luck, but somehow I thin

"Good luck, but somehow I think you may have more than one week of maintenance ahead (keep 'Murphy' in mind, he is still around).
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