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blackcreek 01-29-2010 08:40 PM

1997 Lt-1 overheating at idle.
Using this post I also suspected problems with my bleed tubes after taking the boat out a few weeks ago. The temp was spiking after coming off of plane and only quickly revving the motor out of gear would bring the temp back down. No problems with temp during cruise, only when coming off plane. My bleed/crossover tube was still connected to the heads at the rear of the motor so I unbolted it with the intention of moving it to the front. Turns out the tube was clogged badly, the banjo bolts and tubing both had enough crud in them to completely block the flow.
A quick way to check for flow in the tube is to feel the small hose that dumps the bleed water into the drivers side riser. If the motor is up to temp the hose should be quite warm because it dumps a small portion of the cylinder head flow overboard. If the small bleed hose is blocked the hose will not be warm and you need to investigate. I swapped the bleed tube from the rear of the motor to the front but I only used the Banjo fittings and cut off all tubing except about an inch remaining on each banjo fitting. I had to use some wire and a very small screwdriver to clean out the banjo bolts which were full of rust and crud. The rest of the tubing was full of rust/crud so I just cut it off and replaced with small water hose and clamps. I will post a picture in the morning of the hose routing I used.
I took the boat out tonight and had no temp spikes at all so it looks like the fix worked.
I always flush my motor out after every use but I have only owned it for 4 years. I guess over the years the steel lines start to rust inside and any dirt just makes it worse. If your bleed tubes are on the back of the motor it is made worse because the crud can settle down inside the banjo bolts and clogs the small passages inside the bolts when the boat is stored.

DooSPX 02-06-2010 11:36 AM

Have you checked your T-Stat's? the LT1 has two I believe.

Ski-me 02-07-2010 08:46 AM

Good place to start. 143 stat and a 160 stat. One of them also has a hole drilled in it as well. Mine did the same thing but basically went into "limp" mode. Found out I had a 185 automotive stat in mine. Check it out.....

blackcreek 02-08-2010 07:34 PM

I changed the engine water pump and thermostats (skidim) last year. I was still getting some overheating spikes but only very rarely until I put it in a few weeks ago after sitting for a month. I did not get any spikes the last time out so hopefully I have solved the problem. If it does it again i will pull the stats again and check them.

Jerseydave 02-08-2010 08:02 PM

Check the impeller. How old is it? It might create enough flow at higher rpms but not enough at idle.

Check your trans cooler for a blockage. Remove the hoses from it and backflush it with a garden hose. Alot of weeds/debris can clog it in no time (happened to me once)

blackcreek 02-09-2010 06:44 PM

Impeller has about 20 hours on it, I pulled the cover and checked it anyway. Tranny cooler is clear also. Boat will run at 160 all day long and then spike after it comes off plane. Rev the motor a time or two then it will idle between 165 and 170 with no problems. Seems like I was getting an air bubble in the heads, pretty sure fixing the bleed tubes cured it. I did not have problems the last time out after clearing the bleed tube out. Crappy weather so I have not had it out again. Next winter project is to replace the fuel sender that quit on me last summer. If you have an older LT-1 checking for a clogged bleed tube might be worth a look.

blackcreek 03-07-2010 09:25 PM

Update on this after going out today.
Moved the bleed tubes to the front of the LT1 last month to hopefully solve overheating spikes. I just used the bleed fittings and then connected across the engine with 1/4 inch hose.

Took the boat out for a full warmup then read the temps with a direct reading thermometer.
The boat held steady at 160 on the dash indicator and about 164 at idle.

Cylinder head temp drivers side after extended idle
And passenger side head temp was the exact same

Passenger exhaust riser after extended idle ran at 115 F.
Drivers side riser ran hotter at idle (165 f) and pretty much matches cylinder head temperature
Once underway the riser temps would even out with the drivers side cooling down to about the same temp as the passenger side. Once at idle the drivers side riser would slowly rise to match the cylinder head temp. Both lower manifolds stayed even temp wise, it was just the drivers side riser. The bypass from each head on the LT1 dumps into the driver side riser and at idle the hot bypass water brings the temp up in that riser.(That's the bypass hose in the last picture) Once underway the greatly increased flow through the manifolds evens the temps out.
No more temperature problems or spikes were noted, nice and stable temps coming off plane now. Keep those bleed tubes clean if you own an LT-1.

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