Wondering if God Hates My Boat - Mercruiser 470/3.7 Idle/overheating issue

[rozicrc]

After 5 years of rebuilding my engine, outdrive, replacing my stringers, transom, and deck, I thought I was done with my boat. Wrong. Took the boat out today after being winterized for around 11 months. The boat was overheating slightly before (no issues with heat gasket/timing/ignition), but now it won't idle at all and is overheating. Used to idle a bit rough, but I put off the carb rebuild. #1 piston is running hot/lean from the plug check, all others marginally lean. I am wondering if I gummed up the idle circuit on the carb, it is vintage 1988 and I did not rebuild it in everything else. Could running lean be my issue all along with running hot (as well as the idle)? Otherwise I don't know what else to check, there is a new impeller, pickup, hose (no I did not kink it on the outdrive), 4" heat exchanger looks good. I was getting ready to acid wash the exhaust riser as I don't know what else to check here.

Help me with the overheating and any carb tricks on this quadrajet!

 

[stonyloam]

Do a compression check, you might be leaking coolant into #1, change the impeller in the outdrive. Change the impeller housing if there is any sign of damage from the overheat. Change the points.

 

[rozicrc]

checked the coolant with strips - no exhaust gases in there so head gasket is good. Already did the impeller, water pump is new, coolant level is good. When I say overheat it is really just running hot - 195F at 3500 RPM. I am tempted to rebuild the carb, but the concern I have is really around the continued running hot.

 

[Rick Stephens]

Thermostat?

 

[awdbare]

Sounds like it was running lean before and is doing so now but worse than before. Checked fuel pressure ? Maybe it is time to tinker with the carb or a new one. Temps are going to increase if your fuel air ratio is very lean, maybe the number one cylinder has slightly higher compression ?

 

[Eric 3.7LX Alpha 1]

Pull the outdrive off and run the engine off a hose by sticking the end of the hose inside the water inlet in the bellhousing.

If it has anything to do with the impeller you will see the difference.

 

[rozicrc]

THanks for the replies. When I rebuilt, I used all new parts on the engine side and the thermostat is opening at 165F (checked with IR temp gun). I am going to pull off the exhaust elbow, as well as soak the carb in carb cleaner. Where is the restriction in the elbow normally?

 

[rozicrc]

the temp is fine up to around 3500, but still on the higher side in the water (~180F)

 

[stonyloam]

Check for obstructions slowing flow through the exchanger: pull the front cap and check for derbies plugging the tubes, especially the starboard set. Pull the aft tube from the exchanger that goes up to the elbow and with a garden hose see if the water flows freely out the exhaust with little backpressure, you may have a restriction in the water passage in the exhaust elbow.

 

[midcarolina]

+1 for what stonyloam said.......... also when you have the heat exchanger open verify the tubes are not fouled ( dirty ) on the ID and OD of the tubes.........
Fouled tubes will reduce proper heat transfer...... and I'm wondering if water sat in the exchanger for the past five years if some nasties grew on the tubes.

 

[rozicrc]

How was clean on rebuild, I ran a gun cleaning brush through it. I honestly can't see what it would be other than the exhaust elbow. I am going to roll it out and soak in clr

 

[rozicrc]

Heat exchanger, not how

 

[stonyloam]

Sounds like you hit all of the high spots, not too much left, you might want to check the accuracy of your temperature gauge with either an IR thermometer or radiator cap thermometer.

 

[rozicrc]

Pulled exhaust elbow and tested with hose. No issues with flow but washed overnight in clr. Still running hot when I take it out. I am at a loss here.

 

[rozicrc]

Could his be overpropped? I am topping out at 4300 rpm when pulling a tube and am wondering if the bogging could be the reason that I am having trouble here

 

[stonyloam]

Don't think so, that is about right for WOT. Still think you need to check the accuracy of the gauge.

 

[rozicrc]

Will check but the switch for the temp alarm and the analog gage agree. Will try to take out and recheck head gasket and analog gage accuracy

 

[stonyloam]

Does the heat exchanger get real hot? It seems there is a flow problem somewhere. The engine waterpump is pretty simple, so it does not seen likely that is it. If the impeller is good, and the exchanger and elbow are clear about the only thing I can think of is maybe a kink in the inlet hose that goes through the transom. If the flow from the impeller pump is good the front of the exchanger should be relatively cool. If you did not replace the impeller housing, that might be worth a try, instal a new OEM housing and impeller. Better than taking a chance on a bad overheat.

 

[rozicrc]

Both the analog gage and the temp switch are off 40f. Confirmed with an ir gun and thermometer. What are the odds. Thanks for the help, looks like I have a slid motor after all.

 

[stonyloam]

LOL, yeah my gauge is off 40F the other way, I just put a line on the outside of the glass for a " normal" reading. Enjoy the rest of the season!