Overheating problem 400 chev

[Jacko1971]

Hi Guys,

I have a Gilflite Laser with a 400 chev rear mount ski boat that has what seems to me an eratic temp guage... I can run for hours at different RPMs & it will stay at about 80 Deg Celsius & at some stage the temp gauge will go upwards to around 110 & back yo 90 within 2 Mins or so. The engine still seems to run fine and does not seem that hot ( I can touch the manifolds and the temp sender and not get burnt ) although I will check with a temp gun this weekend to make sure.
What I have done already - checked impellar, all good, new last season with new pump. Checked for blockages, none. checked thermostat housing (I dont run a tstat) all good. Checked gauge & it pings both ways, all good. Replaced temp sender unit, found a loose ground from the battery to the engine and fixed & soldered. Checked & cleaned thru hull pick ups.

I am taking it out this weekend to see if it is still happening and hopefully I have fixed it, I am just after some more ideas from the gurus to check before I go. Thanks

 

[Bondo]

Re: Overheating problem 400 chev

checked thermostat housing (I dont run a tstat)

Ayuh,.... I donno who marinized yer 400 SBC, but every marine T-stat housing I've seen, uses the T-stat to help direct water to where it's gotta be....
Knowin' how Overheat prone the 400 is,...
I'd put a T-stat in it,... Just fer S&G's....

Got a picture of it's piping,..??

 

[Jacko1971]

Re: Overheating problem 400 chev

Thanks mate, I am in Australia & hardly anyone here uses one, Not sure why? Would the thermostat keep it cooler if it runs hot without one? I dont even know if it is running hot yet or if it could of been electrical but am willing to put one in if thats what you think....

Thanks

 

[Jacko1971]

Re: Overheating problem 400 chev

Any other ideas guys ???

 

[GMC2003]

Re: Overheating problem 400 chev

Engine circulating pump?

 

[Jacko1971]

Re: Overheating problem 400 chev

seems to have good flow, I have noticed I have only got 10.5 volts to the back of all gauges & ignition though (I think it still should be 12V), so maybe still some electrical voltage drop to find ???

 

[Lyle29464]

Re: Overheating problem 400 chev

If you have low voltage do to bad wires, wire size or conections your guages will change when a load is put on the circuit. You can test it by manual operation of bilge pump or some other item that pulls some amps. If your float switch is turning on it will change readings on a weak system. The gauges should be on the motor harness not the boat harness

 

[GMC2003]

Re: Overheating problem 400 chev

I couldn't give you a positive answer on that one... I think your idea with the temp gun is good. Just measure the manifolds, block, and around the temp sending unit when it's running normal and then measure them when the gauge is reading on the high side. You might could post a thread in the Electronics section and see what those guys say.

 

[Lyle29464]

Re: Overheating problem 400 chev

seems to have good flow, I have noticed I have only got 10.5 volts to the back of all gauges & ignition though (I think it still should be 12V), so maybe still some electrical voltage drop to find ???

Your charging system should put out over 14 volts I would check that first.

 

[Jacko1971]

Re: Overheating problem 400 chev

If you have low voltage do to bad wires, wire size or conections your guages will change when a load is put on the circuit. You can test it by manual operation of bilge pump or some other item that pulls some amps. If your float switch is turning on it will change readings on a weak system. The gauges should be on the motor harness not the boat harness
I havent noticed that but will check Saturday as well, the gauges are on the motor harness

Your charging system should put out over 14 volts I would check that first. Charging around 14.4V

Driving around not knowing if your motor is running hot or not sucks - As I say drives perfect in every other way but temp says different - should I just throw the Temp Gauge overboard lol....

 

[Jacko1971]

Re: Overheating problem 400 chev

If you have low voltage do to bad wires, wire size or conections your guages will change when a load is put on the circuit. You can test it by manual operation of bilge pump or some other item that pulls some amps. If your float switch is turning on it will change readings on a weak system. The gauges should be on the motor harness not the boat harness
I havent noticed that but will check Saturday as well, the gauges are on the motor harness

Your charging system should put out over 14 volts I would check that first. Charging around 14.4V

Driving around not knowing if your motor is running hot or not sucks - As I say drives perfect in every other way but temp says different - should I just throw the Temp Gauge overboard lol....

Ok, checked ignition last nite - 12.36V, checked all gauges only 10.7V, found in-line fuse and cleaned terminals and checked again - 12.36V, I am hoping that this was the problem and I have fixed it, am taking boat out in morning to check & still will check with Themo Gun for correct Temps..... Will let you know how I go on monday, thanks for all the assistance so far.

 

[Jacko1971]

Re: Overheating problem 400 chev

Hi all,

Just a follow up on my temp problem, turned out to be a $2.00 in line fuse holder behind dash from ignition, replaced that and now all is good, constant and correct temps. Amazing what a voltage drop of 1.5V do to sends gauges heywire ! Thanks to all for your help.