Alarm driving me crazy...

[clinche]

Hi guys,

My 5.7L V8 carbureted engine (small block) overheats at 4K rpm. I cant rely on the temp gauge as it goes crazy sometimes so i decided to monitor the engine with the laser temp reader. When the alarm goes off temperature reading at the thermostat is at 140-150 (my thermo is set at 140), left riser 180 and other riser around 200. I was told that this is normal and alarm shouldnt go off at these temperatures since it relies on the temperature at the thermostat.

Drive gear oil is ok and oil pressure is around 70-80 which i was told is ok as well.

I will be replacing the thermostat kit with gaskets and thermostat sender unit(perhaps it will solve the erratic temperature gauge) and also replacing the temp alarm sensor hoping that this will be the culprit of the alarm going off.

Any more ideas on what i should check guys?

 

[jerryjerry05]

Re: Alarm driving me crazy...

More info!!!! Year,make,recent repairs etc.
It sounds like the risers could be clogged or it needs an impeller and maybe,maybe,maybe.More info needed.J

 

[Chris1956]

Re: Alarm driving me crazy...

It doesn't sound like the motor is overheating at all. The risers are a bit hot, but that happens when they get older.

 

[clinche]

Re: Alarm driving me crazy...

More info!!!! Year,make,recent repairs etc.
It sounds like the risers could be clogged or it needs an impeller and maybe,maybe,maybe.More info needed.J

risers, manifolds, thermostat, impeller all changed. Engine year 2000. 4months in saltwater and rest of year on land..

alarm sounds at around 4K..i lower throttle to around 2000K..alarm goes off after a while..i climb back to 4K sometimes it comes back and sometimes not..

 

[Dave1251]

Re: Alarm driving me crazy...

Sound like you are changing parts without finding the problem first. First find out if it is oil pressure or engine temp that is sounding the alarm.

When you are having the alarm go off disconnect the sending unit of engine temp alarm and see if the alarm stops. Than you will know if its oil pressure or engine temp. Make sure it is the right sending unit as some engine have seperate temp sending units for the gauge and the alarm.

 

[clinche]

Re: Alarm driving me crazy...

Sound like you are changing parts without finding the problem first. First find out if it is oil pressure or engine temp that is sounding the alarm.

When you are having the alarm go off disconnect the sending unit of engine temp alarm and see if the alarm stops. Than you will know if its oil pressure or engine temp. Make sure it is the right sending unit as some engine have seperate temp sending units for the gauge and the alarm.

is it easy to disconnect when cruising at around 4K ?

 

[havasuboatman]

Re: Alarm driving me crazy...

You ARE overheating your engine. 200 degrees at the risers not good. You should be able to touch those things running wide open.
The reason the alarm is turning off at the lower RPMs is that you are getting more water volume at the lower RPMs.
Instead of replacing the equipment that is screaming at you, try replacing the fresh water pump AND housing. You have wear in there and the impeller is losing its seal against the housing or wear plate. This causes lowered water pressure, which means loss to your heat transfer efficiency.

 

[clinche]

Re: Alarm driving me crazy...

You ARE overheating your engine. 200 degrees at the risers not good. You should be able to touch those things running wide open.
The reason the alarm is turning off at the lower RPMs is that you are getting more water volume at the lower RPMs.
Instead of replacing the equipment that is screaming at you, try replacing the fresh water pump AND housing. You have wear in there and the impeller is losing its seal against the housing or wear plate. This causes lowered water pressure, which means loss to your heat transfer efficiency.

Is the water pump you are making reference to the impeller? or the water circulation pump attached to the block of the engine? I changed the impeller.

 

[Bondo]

Re: Alarm driving me crazy...

I changed the impeller.

Ayuh,... But what about the Housing,+ wear plates that come in the Full Kit,..??

 

[clinche]

Re: Alarm driving me crazy...

yes bondo..i bought a new kit and had everything replaced..

so is the overheating causing the alarm to go off even though temp at thermostat reads 140-150 with laser temp gun?

riser reading 200 is not normal at 4K?

 

[Bondo]

Re: Alarm driving me crazy...

Ayuh,... The alarm should Not be sounding if it's mounted in the T-Stat housing,+ it's only 150?....
The risers at 200? says you have a Blockage somewhere....
Start pulling some hoses to see where it's flowing,+ where it Ain't....

 

[clinche]

Re: Alarm driving me crazy...

Ayuh,... The alarm should Not be sounding if it's mounted in the T-Stat housing,+ it's only 150?....
The risers at 200? says you have a Blockage somewhere....
Start pulling some hoses to see where it's flowing,+ where it Ain't....

correct me if im wrong..

so i have 2 problems independant from each other..

the alarm could be going off for some different reason and the risers are gettin hot due to some blockage which is causing overheating and not being detected by the alarm..

correct?

never a dull moment

 

[Bt Doctur]

Re: Alarm driving me crazy...

alarm sensors are water, oil, drive oil. Any one can cause the alarm.Could there be a "water flow" alarm on the newer engines?

 

[clinche]

Re: Alarm driving me crazy...

Ayuh,... The alarm should Not be sounding if it's mounted in the T-Stat housing,+ it's only 150?....
The risers at 200? says you have a Blockage somewhere....
Start pulling some hoses to see where it's flowing,+ where it Ain't....

i pulled all the hoses at idle and i think i have adequate flow. Problem is being caused at high revs which i can not test on land...

any ideas on what other checks i can do. Since the boat is on land i cant even test it out...

 

[jerryjerry05]

Re: Alarm driving me crazy...

New impeller.Was the old one ok when it was removed? Were the vanes intact? Remove the hose at the oil cooler to see if there is junk in the cooler.
When you replaced the impeller was the pump re-assembled right?Was the connecting pipes and lines connnected?If the pipe was installed crooked or the plastic fitting tilted it will restrict the flow.
Check the thermostat for junk or installed wrong.The riser gaskets could be in wrong.The flappers in the exhaust could be stuck.Lots of little things.Keep digging.J

 

[havasuboatman]

Re: Alarm driving me crazy...

JerryJerry has you on the right track. As you get the boat into higher RPM's your boat needs more water volume to regulate the extra heat. YOU have a restriction keeping that extra volume from being achieved. Once you bring the RPM's back down, you are back within the range of heat transfer. That's why your engine cools back down.
Look for any pieces of old impeller. It only takes a little bit of blockage to screw up the whole system. If you can't find anything in the water passages, look to the risers.

 

[nrob84]

Re: Alarm driving me crazy...

hey just throwing in my 2 cents, when i baught my boat it needed a new impellor, when i took it all apart i noticed a few of the impellor blades that broke off fell down into the inlet on the outdrive, easy to check, just take off the inlet covers and make sure its not blocked there. never know could solve all your problems...

 

[las165]

Re: Alarm driving me crazy...

Had a similiar problem. Turned out that some debris made it through the raw water pump and partially plugged one of the outlets to the riser at the thermostat housing unit. No one believed us when we told them it was a small fish until we showed them the remains. Good luck

 

[clinche]

Re: Alarm driving me crazy...

New impeller.Was the old one ok when it was removed? Were the vanes intact? Remove the hose at the oil cooler to see if there is junk in the cooler.
When you replaced the impeller was the pump re-assembled right?Was the connecting pipes and lines connnected?If the pipe was installed crooked or the plastic fitting tilted it will restrict the flow.
Check the thermostat for junk or installed wrong.The riser gaskets could be in wrong.The flappers in the exhaust could be stuck.Lots of little things.Keep digging.J

yes the old one was fine however there was a white plastic tube which was a bit deformed indicating that somethin was overheatin down there but mechanic just threw it away and said that this piece was irrelevant..is this the plastic fitting you are refering to?

I tried removing and checking the oil cooler however i cant manage to work behind the engine..its impossible to work over there..

Thermostat was replaced and no junk in there however i will be replacing the stat gaskets because my temp gauge gives erratic readings. the culprit im thinkin are the gaskets..no ground..while im in there i will be also replacing the stat and temp sender and temp alarm switch..

any more ideas please let me know..

 

[clinche]

Re: Alarm driving me crazy...

JerryJerry has you on the right track. As you get the boat into higher RPM's your boat needs more water volume to regulate the extra heat. YOU have a restriction keeping that extra volume from being achieved. Once you bring the RPM's back down, you are back within the range of heat transfer. That's why your engine cools back down.
Look for any pieces of old impeller. It only takes a little bit of blockage to screw up the whole system. If you can't find anything in the water passages, look to the risers.]

can u please guide me from where to start checking the water passages so i make sure im doin everythin right?