4.3L V6 Correct Operating Temperature

[frank1492]

As reported in another post I recently had my old 1988 4.3L OMC 4bbl replaced with a remanufactured Merc long block (identical block.) I currently have about 6 hours on the engine and therefore am in the break-in phase. This involves keeping the RPMs between 1500 and 3000 rpm (about 3/4 throttle) and varying the engine speed.
I have yet to see the engine temp above 125 d. even if I keep the engine at 3000 for over 5 mins. The dealer says this is normal, but I'd like your opinion- seems too cold to me. I do have brand new one-piece OMC manifolds on the engine (yes I actually found some!) whereas before the ports on the old ones were probably restricted somewhat causing the engine (my recollection) to run considerably hotter at 3000.
My understanding is that the pistons are elliptical when cold, and engines should not be run at high speeds when too cold for that reason.
Could someone set my mind at ease that my conditions are normal? I will not be running the engine at full throttle for another 4 hours, and then only sparingly.
Your help is very much appreciated!!
Frank

 

[gallmond]

Re: 4.3L V6 Correct Operating Temperature

My 4.3 runs at 170-175...I thought that mine was running too warm. So I would be happy to hear what is the normal range too!

 

[IVAZ]

Re: 4.3L V6 Correct Operating Temperature

I don?t know on an OMC. My 4.3 Merc runs about 130-135 degrees at anything below 3000 RPM's. At 3500-4000 RPM's it?s about 150-170 degrees. At 4000-4800 RPM's it stays at about 140-145 degrees.
Your numbers don?t sound bad to me.

 

[Polar_Bus]

Re: 4.3L V6 Correct Operating Temperature

My 5.7L 2bbr runs at 160F, engine runs perfect...

 

[frank1492]

Re: 4.3L V6 Correct Operating Temperature

Still looking for more info here...thanks to all who have responded so far. To Gallmond, I do think you are a little too hot. Most thermostats are designed to open at 160 d. I used to change my OMC water pump every season to rule that out as a cause of overheating. That would pretty much leave the manifolds which in your case may be starting to plug up.
It would be useful to me to know how long it took (approximately) to get to 160, and at what speed the engine would have to be run to get there.

 

[frank1492]

Re: 4.3L V6 Correct Operating Temperature

I don?t know on an OMC. My 4.3 Merc runs about 130-135 degrees at anything below 3000 RPM's. At 3500-4000 RPM's it?s about 150-170 degrees. At 4000-4800 RPM's it stays at about 140-145 degrees.
Your numbers don?t sound bad to me.

This is reassuring, though I would wonder why the temp actually falls at higher operating speeds.

 

[IVAZ]

Re: 4.3L V6 Correct Operating Temperature

I think it has to do with the impeller spinning faster pumping more water.

 

[Polar_Bus]

Re: 4.3L V6 Correct Operating Temperature

I don?t know on an OMC. My 4.3 Merc runs about 130-135 degrees at anything below 3000 RPM's. At 3500-4000 RPM's it?s about 150-170 degrees. At 4000-4800 RPM's it stays at about 140-145 degrees.
Your numbers don?t sound bad to me.

I don't think your thermostat is working correctly. Your engine temps are all over the place. The function of the thermostat is to stabilize engine temps at a certain temp (usually between 160-180F )

My engine stays right at 160F after warmup.

 

[cwoodffr]

Re: 4.3L V6 Correct Operating Temperature

87 LX was running too cold (120 or less). I pulled the original stat and popped a new 160 in. It now gets up to the stat temp within 5 mins of startup and stays rock solid at that temp no matter what rpm or usage patterns (cruising, tubing, putting).

BTW, I assumed the old stat would be stuck open, but it was closed when I pulled it and when I boiled it it opened....still was faulty.

 

[tazzerblue]

Re: 4.3L V6 Mine is 142 t-stat.

Re: 4.3L V6 Mine is 142 t-stat.

MY 4.3 is a 1993 model SN OD836866 and the book says 142. some other unit have a 160. its all by SN #. I just replaced mine and checked the sender for the correct ohm's at different temps and it checked out fine.
idleing with the ear muffs gauge said 140.
So you still don't have answer. An engine should'nt run alot cooler because of exhaust manifold. the t-stat controls temp. you could have cooler ehaust temp,did you shoot them with an IR gun?