Mercruiser MIE 340 "Overheating issue"

[johnbeach20]

I'm having an overheating issue on my Inboard Mercruiser MIE 340 454. I'll start by telling you what repair I have done.
Last month when I took the boat out it started out fine. I use the boat as a dive boat. I drove the boat out approx 1.5 miles to a dive site on the lake. killed the engine and we all did the dive. I went to start the motor up and it would turn over. I processed to bump the switch and it started turning over and started. I thought the batteries were drained down and my alternator wasn't working. I started back across the lake to another dive site and tie the boat off. We did the second dive and was ready to come back in. The motor didn't want to turn over again. my jump box didn't help. I normally never go fast on the lake it's not that big and there is no need too. I decided to bring the RPMs up to 2000. I normally idle around the lake. The Motor didn't like it and started knocking at about 1500. I backed it back down to idle and finished loading the boat on the trailer.

Skip a few days and I decide to go out and look over the boat. I discovered water in the oil. I thought Head Gasket and started to dig into the motor. come to find out that the heads and head gaskets were fine. I turned to the manifold and found one had a very bad crack. and bought new manifolds. I started flushing the motor and discovered that the camshaft was wiped on three lopes and lifters. I decide to change it instead of buying another motor. I got everything back together and started it up. sounded great. I had to wait to break in the cam due to the water flow needed to keep it cool for 25 mins at 2500rpms.

skip a week and we are at the lake. I put the boat in and open it up across the lake. I couldn't get it past 2500 rpm due to the timing being off and it would backfire through the carb. I ran if for 20 mins and it started to reach 200f probably 17mins in the run. we did a dive and started to move to another site and it reached 200 again right before we reached the site. we are probably 4 miles out. we did the dive and started back and I was running 2400ish rpm at about 17mph it stayed at 200 degrees. I didn't get a chance to look into the time I frankly don't know what its supposed to be set at. Could this be why I'm running hot? should I pull apart my cooling system RAW water? I'm planning to change the Impeller and fix timing before I take it back out next week. What should the timing be set at?

 

[alldodge]

From what I'm reading it appears that maintenance is the last thing on your mind. Motor getting hot, timing is off, motor knocking, just keep going have to dive

Always good to know what year the motor is, and serial numbers are best. Being a 340 inboard I'll guess its between 1981 and 1987.

Start with taking the seawater pump apart and replace impeller and maybe even the housing if damaged. May just need wear plates, but need to inspect to see what your working with

Timing 8 BTDC
Plugs MR43T or RV8C gap at .035
Point gap /016 to .019 dwell 26 to 31 degrees

 

[johnbeach20]

Maintenance Isn't the last thing on my mind. The first day out it wasn't running above 160. on the outing after rebuild, I have to run the whole break-in process so the cam breaks in right. I'll rebuild Raw water pump and set timing. what rpm are those timing settings at?

The boat is a 1984 Sportcraft 270 and I'm assuming the motor is the same age.

 

[alldodge]

Manual 3 and 9 show 8650 to 700 for idle

If you said what year you have I wouldn't need to check both before answering, which makes it a tad easier

 

[Scott Danforth]

200 is way too hot for a motor in a boat. that is lack of flow which means you toasted the rubber bits in your exhaust system and probably caused other issues

start with your raw water system. if any of the vanes are missing, you have to pull the system apart to find the pieces

my guess this is a new to you boat.

the first thing you should have done when you brought it home is put it on the hard, then do every bit of maintenance

the following is the minimum:

• oil and filter change
• compression check
• raw water pump and sea strainer service
• prop gland packing check
• rudder gland packing check
• trans fluid change
• plugs, cap and rotor
• verify the timing - adjust as needed
• verify the shaft alignment
• change fuel filters
• verify choke setting

 

[johnbeach20]

I want to run an update by you all. I pull the raw water pump off and inspected. wasn't anything broken but it was time for a rebuild due to cracks and it wasn't really holding its shape. I had a kit on hand as I was planning to rebuild anyway. I decided to pull the how system apart and clean and replace the hoses and clamps etc.

I found several broken impeller pieces in both the trans oil cooler and the Engine oil cooler. I cleaned everything out and reassembled it. planning to take it to the lake this weekend for another test.

I do have a question. since this engine is raw water cooled what gaskets are supposed to be installed between the manifolds and risers.

Thanks

 

[achris]

...The boat is a 1984 Sportcraft 270 and I'm assuming the motor is the same age.

That's a dangerous assumption. Can you get us an engine serial number?

Gasket between manifold and elbow (do you have risers?) should be 'full flow'...

Looks like this.......



Chris......

 

[johnbeach20]

Chris, the serial number is 6397468

The reason I'm saying that the motor is the same age is just to confirm the model is an MIE 340 Mark IV 454. I have paperwork showing the motor was rebuilt back in 2008. it could have been swapped or rebuilt. When I took it apart it was Bored .060 over. I'm very mechanical I've just never messed around with a cooling system like this.

also, those gaskets are the ones I placed in riser elbows. That is what I received when I ordered the parts and told them it was raw water cooled. I didn't know if it was supposed to be the 4 slotted instead.

I'll give an update Sunday after the lake run.

Thanks for the help

 

[alldodge]

Should be the 2 slot, the 4 large slot are for when risers are used.

Name clarification
Risers are square blocks that go between manifolds and elbows (lower right)
Elbows can be both mounted on top risers and manifolds

 

[johnbeach20]

UPDATE!!!

I took the boat out Sunday and the results are an improvement. Temp on Guage stayed right at 180-183F. After timing was set the backfiring vanished. I ran it at about 2500rpms for about a mile. I started hearing a ticking noise like a lifter or valves. we stopped at an island and checked over everything torqued the intake manifold and tightened belts etc. I started it up and still had a ticking noise. I was irritated at this point and asked my wife could we buy a new motor if I blew this one. she said yes and I took off WOT for about 10 miles and about 3 miles in the ticking stopped and the temp stayed the same. no steam out the exhausts and it sounded great. I radioed my buddy that came out on his boat to help if we broke down. I told him to turn around and I went WOT all the way back another 10 miles. we stop at the island again and looked everything over and intake manifold gasket was leaking oil towards the 7 and 8 cylinders I figured when it ran hot last trip it cooked them I order new ones and new valve cover gasket and a stud kit.

Do these temps sound good or do they need to be lower? lake temp was around 83F idk if that has anything to do with it. I will be testing my temp gauge this week.

Also
Thanks for the help

 

[achris]

That temperature is great...

 

[johnbeach20]

That's good to hear. I believe I'll be ready to go after I reseal the intake and set timing again.

Thanks Again