Run Time At W.o.t.
 

I know this is a very general question but is there a rule of thumb of how long time wise you can run a stock 502 mag mpi at w.o.t. ? I normally run in the 2800-3400 rpm range 95% of the time. There are times I will run 4800-4900 r.p.m. for 10-15 minutes.In the Merc. book they say after 10 hrs of use during break in you can run w.o.t. for 5 min. max at a time. After the 20 hr. break in they just say refrain from prolonged operation at maximum ( full throttle )RPM. Whats prolonged? I am just looking for some opinions/experiences of others on this. I just dont want to give my engines a early demise. Thanks in advance.

Use full synthetic oil and monitor the oil temperature if you're going to run WOT for that long. It's no guarantee, but at least you're stacking the deck in your favor.

You may want to put a bigger oil cooler in too.

The only rule I know is The harder you run the more you spend.
Jim

You can run WOT until something goes boom.:cool-smiley-011:

Run WOT till you pass whoever is in front of you then back off and wave!

Been on several 50-75 mile runs in a stock 502 powered 1995 Baja 272
with WOT segments lasting as much as 30-45 minutes.
Engine still hummin' beautifully!

Thanks these are the real world replies I was looking for.

Exactly.
There's nothing worse than the sound of an engine coming apart the hard way.

Oil temp is most important when doing this. Do not exceed 300F, target temp is just above water boiling, around 212F but you won't be able to keep it there at WOT.

Also, check the oil level frequently when running like that. Oil consumption may go way up under those conditions.

If water and oil temps stay within limits, and oil level is checked frequently, it should be OK.....

I ran 40 miles nonstop this weekend at 4500rpms. I opened it up off and on during this time. If the oil temp gets up to 230* I would ease up till it cooled off a bit and nail it again. Oil temp should dictate your runtime at WOT.

Sure oil temp is important... BUT I WOULD BE concerned with the valve train...

Replacing the one head today on my 454mag. DME says it cracked from running WFO too long and stock cast iron heads don't get rid of the heat fast enough. Whatever this is worth???????

last i ran the boat was wide open for about 4-5 min then cruised 4200 the rest of the time. Oil never got over 208f, that was with a stock oil cooler, but was a 97 350 mpi.. Beat on it pretty good now, no problems as of yet.
John

Alllllllll Dayyyyyyyyyy

I like to hold them WFO until a valve drops........ Then shut it down and call for help

Wide Open for 15-20 minutes on a regular basis

I ran a pair of 500 EFI's from Palatka, FL back to Jacksonville WOT the entire way which is approximately 70 miles.

I had a Merc certified mechanic on board who can confirm that we never let off.

The engines never missed a beat but the outdrives got a little chalky.

I have always ran Mobile 1 15W50 and change at 20 hours or less (less if I run hard on a poker run).

Not sure I recommend this however my mechanic told me that these engines really don't know the difference between 3500 RPM and 5200 RPM. If it is all good they are good, if something is going to break it will break.

if it is a stock big block 502 i would not be scared to hold it open for a hour............I run my 540 for extented bursts at 6200 rpm, granted it is built with good parts........That is why merc gets the big money for there motors..........

In my view there is a difference to be made, here.

If your boat is propped so that the motor can easily run at or very near to its designated max revs, then you can probably run that for as long as you like. But, if the motor loads up and is several hundred revs under, it will be generating alot of heat, although the revcounter tells you you´re on the safe side. Its like running a tow rig in in a high gear up a hill.

I run my 525 flat out as long as I need to get ahead or stay ahead, and sometimes that has been a 45 minute blast. The oil temp never goes over 185 degrees, pressure is 55 psi, the water is rock solid at 165 degrees.. I watch the drive temp alot though, because it goes up from 220 to 270 degrees, when the last few ponies are called out.

After the funs over and the motor comes back to idle, there is always around 35psi oil pressure. I still use the stock Merc mineral oil, but also change it at around 25 hours, depending on
how those hours were run.

Its not revs that kill a marine motor, its load.......and the same applies to the drive.

If I was going to run a stock 502 at wot for sustained periods of time I would install drive temp gauges,oil temp gauges,run synthetic oil and probably bigger oil coolers as the factory oil coolers are tiny. Once it has been running wot for a few minutes it should stabilize at a certain temp and stay there,if it continued to climb it would self destruct. I once ran my procharged 502 at wot for almost 1/2 hour a few weeks before I pulled it out to rebuild it, I had cheesy comp roller tip rockers that still used stock style fulcrum balls. When I tore it down they were blued real bad and galled plus one was split in half but hadn't let valve train fail yet miraculously. I have since always used roller rockers. Stock valve train can fail in 502's,I have seen lifter snap rings blown out and similar problems on tore down warranty motors so its something to think about,Smitty

Hmmm lets see ....70 miles .... less than an hour ?