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454 XLI high/fluctuating temp

C

CTII pilot

Member
My port engine is running hot. It levels out about 180 at idle (starboard is about 160). But even at idle will bounce up to 210 and momentarily up to 220 and then will come back down again to 180. I never get an overheat alarm which I believe is set to 210. When I run it it will get up to 210 or higher after a few minutes until I bring it down to idle. I just got the boat and was getting hotter on sea trial. The surveyor recommended getting the heat exchanger boiled. I cleaned the sea strainer this weekend and also back-flushed the oil cooler.

Tonight I was going to switch out the sender lines to the other gauge to see if it was a gauge error. However, due to the way it wired I didn't want to pull it all apart tonight. The port oil pressure and voltmeter also momentarily pulse about a needle width every 15 seconds or so while the starboard gauges are rock solid.

Any ideas?
 
thanks. thermostat was just changed on that engine two weeks before I bought it...actually, the first time I went to look at the boat the thermostat was out so we couldn't run the engine.
 
That tells you the port engine has had a heating issue for a while.

I'd start with the IR thermometer and verify the accuracy of the gauge.

Any service history available?

Measure the raw water pump's output for item #2.
 
When I originally pulled off the pressure cap and checked the coolant it was full..i.e. a small amount ran out. I just checked it today and put my finger down in the pressure cap and couldn't feel any.
 
Sounds like it is time to get a cooling system pressure tester and find out where it is going. Check the oil level and make sure is it NOT over full.
 
Any chance could be a big air bubble causing the fluctuations? I will check the fluids again when I go to the boat but they have been normal. Where is the best place to get a cooling system pressure tester?

Bigger issues on the other motor though. When I bought the boat the surveyor couldn't get out one of the spark plugs. Part of the pre-purchase arrangement is the sparkplug had to be removed, check the compression and replaced. This was completed and called by a reputable dealer who did the work and said it was good to go. I had a mechanic on the boat on Tuesday to look at the manifold which I thought was leaking (identified at survey and repair negotiated into the boat price). He found that when unsticking the sparkplug some serious damage to the head and seat had taken place. Now we are looking at a head replacement.
 
Uuugh! Been there, done that. Had to pull the head and drill the old plug out.

A message to all: Never, ever install plugs in a marine engine without putting anti-seize on the threads!

Jeff
 
CTII - I had a very similar problem on 350 engine. My engine would climb to 200+ degrees when running at slow cruise around 1800RPM's. I could usually get the temp to drop if I throttled up to around 2400RPM or if I pulled backe to 1000RPM. I changed the thermostat at the heat exchanger and the problem never happened again. Being a novice mechanic, I did not even know there was a thermostat at the heat exchangers until doing a little research on this site!
 
I just changed the thermostat (#6). THe housing is a rubber housing and should not need to be replaced. The housing has an offset lip that acts as the gasket so there is not even a gasket to change. Good luck!
 
FastJeff, Could you tell me if these engines should also have the second thermostat at the circulating pump? One schematic I found showed a 160 degree thermostat at the pump as well as a 170 degree thermostat at the exchanger. It seems redundant to me but thought I would check it out.
 
You need to look at the breakdown for your application....one thermostat (for the coolant) per engine. The newer design blocks have 'remoted' the thermostat in many applications.
 
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