4.3L thermostat or sensor?

[jrampey]

I need a little help - I have a 07 Tahoe Q6 with 4.3L Mercruiser ser#0W638393... open cooling systerm. Last couple of times last fall and again this week I intermittently got a warning beep (Continuous beeeeeeeeep) while cruising. A quick glance at the gauges showed no faults. good oil pressure, temp at 180, 13+ volts. First time or two I throttled back and it quit beeping after a few seconds. Watching more closely the alarm is related to engine temp... as the gauge approaches 180 it alarms. Growing annoyed-this week I didn't throttle back - and after 30 - 60 seconds it quit alarming and I could see the temp drop 10? degrees. Several times through the day it alarmed - everytime when temps hit 180... then within 2 minutes the temps dropped back to 170 and the alarm stopped.

So - is it a sticking thermostat? or a bad sensor? or both. 180 seems low for the alarm to sound! Back in the fall I could justify the engine being a little warm - lake water temps were near 90... this week they were 52!

I looked at parts online - thought I would get a thermostat and sensor, but, where is the sensor - are there two? one for the gauge and another for the alarm?

Someone share your wisdom and point me in the right direction. Thanks in advance.

 

[achris]

Re: 4.3L thermostat or sensor?

Carb or MPI?

 

[jrampey]

Re: 4.3L thermostat or sensor?

Carb

 

[achris]

Re: 4.3L thermostat or sensor?

ok.. 2 sensors, one (analog) for the temp gauge, one (switch) for the alarm. If the gauge and the alarm are 'indicating' the same thing at very closely the same time, I believe you may have a genuine problem, and it does sound like a sticky thermostat... When you get a new one, and gaskets, make sure you get genuine. The gaskets on the Mercruiser are different to automotive. If you put automotive gaskets in, you'll be back here asking why your temp gauge doesn't work any more. The genuine gaskets have brass rivets in them for ground conduction, which the sensors need....

 

[Pete104]

Re: 4.3L thermostat or sensor?

How long has it been since you had the water pump replaced?

 

[jrampey]

Re: 4.3L thermostat or sensor?

Raw water pump in the lower unit was replaced last winter. Never have touched the circulating pump.

 

[Pete104]

Re: 4.3L thermostat or sensor?

Typically, to new to need a circ pump.
Just wondering about raw water pump, since you stayed in it & it cooled down.
Are you the original owner? If not, how far from salt are you?

 

[jrampey]

Re: 4.3L thermostat or sensor?

Its never been in salt water... 250 miles to the coast - been hankering to take it down there but not yet. Looked at Mercury parts express... looks like two different thermostat housing configurations... I'll have to look at the engine tomorrow to figure which one is correct. I may get both sensors - I can't tell from the descriptions which is which $25 - $30 each. My logic is: If the gauge sensor is bad then I'm looking at an erroneous temp on the gauge... 180 seems low for the warning buzzer. If I get both I should be good.

What is the temp rating of the OEM thermostat? I saw 160 and 170 types listed... I've heard of others as cold as 140.

And, one more note... just before this all began I adjusted the engine timing - according to the manual - spec is 10 btdc. It was at 8 before I adjusted. First time in 20 years I've been able to use that fancy timing light and dwell/tach meter! I noticed little or no performance change or temp difference.

 

[dubs283]

Re: 4.3L thermostat or sensor?

did you follow the corrct procedure for adjusting the timing as per the oem manual??

you need to set the ignition module to service mode to set the timing, otherwise this can cause issues like detonation, runnability issues, and...overheating problems

 

[jrampey]

Re: 4.3L thermostat or sensor?

Yes, "according to the manual" I did follow the procedure in the manual.

 

[Pete104]

Re: 4.3L thermostat or sensor?

Older motors were running the 140 degree stat. Newer (vortec style) run a little warmer.
Your engine has 3 critical sensors. High temp, low oil pressure & low gear oil.
Recently Don & chris set me sraight on verbage, Thank you!

Those sensors are on an "open" (NO=normally open) circuit. If 1 of them are "closed", the alarm will sound. The curcuit would be complete. With that in mind, if you can run it again & make it act up, unplug it. The alarm should stop.

Chris had a response to a post a couple weeks ago that only used NO. I don't know why it didn't click or register with me, so I posted something like "What is NO"? Don replied with "NO" means normally open & "NC" means normally closed.

mods if you would be so kind to loose post #12,13 & 14

 

[achris]

Re: 4.3L thermostat or sensor?

Chris had a response that only used NO & NC. I was WTF? Don straightened it out with NO = normally open & NC = normally closed!

Hey... are you having a go???

 

[Pete104]

Re: 4.3L thermostat or sensor?

I got WTF down pat!!

Please enlighten me on "go"!

 

[achris]

Re: 4.3L thermostat or sensor?

I got WTF down pat!!

Please enlighten me on "go"!

Having a go (at me)...

 

[jrampey]

Re: 4.3L thermostat or sensor?

ok, ok, ok guys calm down... Thanks Pete, and Chris, and Don... you got me thinking. I'm going to take out the sensors and place them in a pan of water and warm them slowly while monitoring the resistance vs temperature... I'll let you know the results.

 

[l8rmike]

Re: 4.3L thermostat or sensor?

Any updates???

 

[Don S]

Re: 4.3L thermostat or sensor?

Welcome aboard l8rmike

If you are having a similar problem, you would be a lot better off to just start a new thread with your engine info and your exact problem. What may be this posters problem may not be your problem.