1995 4.3 LX Overheat - or not

wireready

Seaman Apprentice
Joined
May 26, 2009
Messages
46
I need info about actual temperatures I should see with my IR thermometer with my 4.3LX 1995 motor. - I tried reading lots of posts about overheating but didn't come across actual temperatures being mentioned around certain parts of the motor.

After running 15 minutes on muffs- I measure 175 or so at the brass nuts that hold the Tstat sensors. the top of the Tstat housing cover- doesn't get above 140.

Can anyone tell me if these seem like normal temperatures and let me know what a "Danger" temp would be- as I want to take it out on the lake for a quick test to see if it behaves differently under load/higher RPM- but I don't want to damage anything.

All over the engine block itself I get readings of 145-165. The tops of risers never get above 100 or so. The Exhaust manifolds are between 155-160 - except where the manifold touches the engine block. Where the gasket is-about 1/2 inch into the exhaust manifold is a hot area -around 200. But I'm wondering if the extreme edge of the exhuast manifold where it meets the gasket should be that hot or not. 99% of the manifolds are 145-165 except right where it bolts to the block.

The block itself isn't 200- just the extreme edge of the manifold where the gasket would be. Not sure if that's normal or not.

I think I'm getting good flow because when I first start- my riser hoses and water pump hose both get cold at first- then the hose going to the water pump gets gradually warmer- and then at about 140- the hoses going to the exhaust mainfolds get warm and hard which I assume means the Tstat has opened as it should.

I have a new tstat and new impeller. I checked and replaced both to see if they would change my temp readings- and they haven't.

Also my RPM on my TACH (which I don't know if it's accurate) only shows about 500, and the idle does seem a little slow.

Would too slow an idle lead to higher than normal temps?

If so I'll adjust the idle up to whatever it should be and see if that changes the observed temps.

Also if anyone has any tips on backflushing- I'm not sure mechanically what that entails and what I use to adapt a garden hose - does it mean just connecting a garden hose at each hose opening at the Tstat housing and forcing water down each hose- to see if it exits at the transom?

What about the block- where would I connect a garden hose to flush the block if I suspected I wasn't getting enough flow?

or do my temps seem fine. I wanted to just keep the motor idling to see how hot it would get and if it would reach equillibrium- but I don't know what the danger temp would be where I could start melting things or damaging the block if I kept going.
 

dubs283

Vice Admiral
Joined
Jul 27, 2005
Messages
5,332
Re: 1995 4.3 LX Overheat - or not

everything you have investigated on your engine seems to have normal readings, the exhaust manifold is going to be hot where you describe due to it exiting hot exhaust gases from the heads right there, no cooling water present at that point, the jackets are more towards the "center" of the manifold

as far as idle speed, check the manual - most are around 650-750 in gear, best to verify with a shop tach/advance timing light, they are quite accurate

it actually sounds like your engine does quite a good job of maintaining normal operating temps based on your observations, a lot of motors have one manifold much hotter than the other but still do a fine job of cooling
 

wireready

Seaman Apprentice
Joined
May 26, 2009
Messages
46
Re: 1995 4.3 LX Overheat - or not

thanks. Sure enough I took the boat on the lake, and the temperature was great. I guess running the 4.3LX on muffs just doesn't give the motor enough flow especially idling. But fully submerged in the water, my temp was running nicely at around 140-150 consistently at all speeds and loads.
 
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