Correct Operating Temp and Possible Vapor Lock

"We're new to boating, but

"We're new to boating, but I've built several hot rods and am familiar with basic engine knowledge.

I have a 1999 21ft Regal with a 4.3 FI MercMarine engine. We usually boat at 5,000-6,000 feet above sea level. After a couple minutes of steady cruising at 3,500-4,000 rpm, temps get up to over 200 degrees and the engine falls on its face. It will idle and run at low rpm's, but feels like it's vapor locking. It will run fine after cooling down a bit. I know 200 degrees is close to normal operating temp in a car, but I'm not familiar with boat operations, and am guessing it's too high.

1. What is the correct operating temp for my 4.3? If it's running hot, what should I check?

2. I'm using cheap 89 Octane fuel and gassing up at the local gas station before hitting the water. I don't think cheap gas has anything to do with the engine heating up, but could it be contributing to a vapor lock problem?

3. Could a dirty fuel filter be contributing to the vapor lock?

Thanks,

Dave"

Is it FWC Fresh Water Cooled &

Is it FWC Fresh Water Cooled (antifreeze in the block w/a heat exchanger) or RWC Raw Water Cooled? RWC check the OD impeller. FWC may have seawater belt driven pump w/internal impeller located on the low starboard front side of engine. Heat exchanger could need tubes rodded out. Is the belt to the front mounted circulating pump tight? I think T'stat temp is 160 F. and engine temp should stay under 170 F. May also need a new T'stat if it doesn't open completely.

"Guy,

I believe the T's

"Guy,

I believe the T'stat in a RAW water cooled engine should be 143. I am not sure if the efi motors use a higher temp or not. Maybe someone with a 4.3 efi motor can chime in.

As far as I remember only the closed cooling engines used a 160 degree thermostat.

Either way no merc engine should ever or rarley get above 180 degrees.Normal operating temps for raw water is 150 to 170, Closed cooling is 160-180

As said probably is the water pump impeller in the outdrive. This is what feeds the engine its fresh cold water.

Also I would do an oil change after this issue is resolved.

A quick test for the OD impeller is to put the ear muffs on the outdrive with the hose connected and turned on. Adjust water flow to a low flow amount just enough so water shoots out of the muffs.
Start the engine keep it at ~ 1000 rpm no more, and watch the water closely. If the water gets sucked in the impeller is working OK. If the water continues to shoot out of the muffs then your impeller is in need of replacement."

KG:

I like the impeller tes

KG:

I like the impeller test. Excellent point for the oil change since the high temps. will break down the oil.

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