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Crusader 350 overheating at idle, normal from 2K and up

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LewT

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On warming up my port engine climbs to 200 and rising. Running up to 2K and more temp drops to 180, matching steady starboard engine. Running boat underway at 2K to 3+K both engines run cool. Good exhaust flow at idle and at RPMs. any thoughts?
 
Welcome to ME.com!!

how old are they? are they "Model 350" or 350 CID engines?

when was the last time the raw water pump was serviced?

how old are the elbows and what body of water does the boat see?

finally, FWC or RWC - heat exchanger or not?
 
1987 350 cid, raw water pump service 18 months ago, not sure of elbows. Runs in salt water and is RWC with an exchanger. Runs normal temps at above 15K RPM, even with load at speed at 2800-3000. Only rising temp at idle. Could it be thermostat?
 
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LewT said:
1987 350 cid, raw water pump service 18 months ago,
A seawater pump impeller that has been at rest for two winters may have lost resiliency by now. In other words, several of the vanes may have taken a "set" by now.
You may want to change it...... and you may as well change out both of them!

not sure of elbows.
Best to remove and inspect the mixing chamber seawater ports.

Runs in salt water and is RWC with an exchanger.
If equipped with a Heat Exchanger, it would be a Closed Cooling System.
A Full System includes the exhaust manifolds...... whereas a Half System would include cylinder block and cylinder heads ONLY.
None-the-less, Elbows are always supplied with seawater.

Runs normal temps at above 1.5K RPM, even with load at speed at 2800-3000. Only rising temp at idle. Could it be thermostat?
Generally, a thermostat either opens correctly, or it does not open correctly. Since it works properly above 1.5K RPM, it is likely OK.

The P of E (process of elimination) will be your best bet.
Look at, examine, test and/or replace one item only at a time.
Click to expand...



.
 
Thanks Ricardo, great suggestions. The engine has been run frequently over the last 18 months since new impellor and sea water pump service. But still I will check that.
P of E is good idea and I'll get started on that.
 
FYI...... a tiny suction breach (in the path from the seawater inlet to the suction side of the seawater pump) will KILL any pump's ability to pull seawater in..... in particular at lower RPM.

One method for checking would be to connect a shop vac to the suction hose (right before the seawater pump) and block off the inlet area.
Then use shave cream on/at any suspect areas.
The shave cream will disappear at the area of a suction breach.
Sounds silly..... but it works!


Pressurizing a system in order to find a suction breach is not quite as goof proof.

Positive pressure for finding a pressure leak!
Negative pressure for finding a suction or vacuum breach!

.
 
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Possibility of a suction breach is a great idea! Thanks, I'll give that a close look in the next few days. Not at the boat till then.
 
Strainer service ports are worthy of a check...

On the raw water pumps, they may be in need of more than impellers....they offer both minor and major service kits.....there are several wear items that should be checked.

and 2x on the elbows....an IR temp Gun would be of benefit in the diagnosis as well, especially the temp of the water going into the elbow and the temp of the elbow itself...
 
I recently had the identical problem with one of my 5.7s. Idleing engine overheated 20 miles off shore while drifting live bait for Marlin. Waited a while, restarted and ran home without a problem. Once back, I checked the raw water flow by removing the heat exchanger zinc and replacing it with a fitting and a short hose. At idle, both engines filled the same 2 quart container with seawater in 28 seconds so I felt I had eliminated raw water flow as an issue. This is a neat, quick trick that I think is a valid test.

After overnight cool down I then found that the coolant level in the offending engine was low. Apparently the air "bubble" would circulate at higher rpms, but get stuck somewhere at lower rpms and cause an overheat. A refill fixed my low rpm overheat problem but subsequent observation showed that the overflow return system was not working. Turned out to be a clogged valve on the coolant cap.
 
Back to both makomark and Ricardo. Still continuing along with you guys' suggestions, I'll try to keep you posted as to the mystery. Thanks
 
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