4.3 heat issue

[martyh]

Hey guys, I want to bounce something off of you and see what you think.

I have a 1988 OMC Cobra with the 4.3. I have had it a few years now and it has always seemed to run hot or at least hot to me, I don?t get to use it very often so I chase problems on it when I have some free time.

The temp gauge is not broken down by easy to read numbers but it seems to run closer to 200 than it does 150 and it just seems too hot. Also, by touch the exhaust manifolds put out more heat than what I think they should as they are hot to the touch after it has been running for a few minutes.

I have changed the raw water pump on the outdrive, it looked good but I changed it anyway. That did not cure the problem. I changed the thermostat, one side of it was broke, the metal tab that holds the spring in place was gone. I am assuming it is in the engine water pump or it?s in the engine block somewhere. I spent some time on the water with it and still no change in temp.

Back at home, I submerged the outdrive in a big tub of water and the water level is above the intake vent screens. I pulled the hose off of the thermostat housing (the other end goes to the oil cooler and then to the outdrive) and started the engine. I was assuming that water should come pouring out of the hose onto the floor when the engine is running. It does not. Next, I removed the raw water pump on the outdrive. It feels warm as if it was turning. Just to verify it was turning, I start the engine again and see that the pump shaft does turn when the engine is running. I reinstalled the raw water pump and go to the next possible block in the line, the oil cooler. I pulled the hose off of the inlet side and start the engine again, and still, nothing. Am I missing something somewhere?

As some of you may already know, according to the service manual, water enters the outdrive through the screens on the side of the lower leg and is routed up through the raw water pump on the outdrive and then through the transom to the oil cooler and then into the thermostat housing where it does it?s direction cycling depending if it?s hot or cold.

I was hoping somebody could shed some light this.

Oh, on another note, I discovered that the original OMC shift cable is still in place. I guess the recall was never done on this one.

 

[Uraijit]

Re: 4.3 heat issue

How long did you give the water to come out? It might take a few seconds. Also, are you 100% sure the drive was submerged enough? This test is a lot easier if you have the boat actually on the water. I would think that your boat would be overheating very quickly if you're not getting ANY water into the engine.

If you're not getting water through the transom, and you've got a new impeller with a good housing, you've either got a blocked pickup, or a blocked outlet tube. Take the lower unit off, and back flush from inside the boat, through the transom. Then take the water pump impeller back out, and flush through the pickup tube out toward the screens. Your blockage has gotta be in there somewhere...

I'm guessing it's an issue with the upper side of things. Since you said your impeller wasn't trashed, it must be getting water into it...

 

[Boatin Bob]

Re: 4.3 heat issue

I don't think you had in enough water, under normal conditions you should be able to pull the input hose off the t-stat and get between 2 to 4 inches of water coming out the hose. Either get a deeper bucket or drop it in the lake and try again.

 

[martyh]

Re: 4.3 heat issue

The outdrive is submerged, and the water line is above the pickup screen vents. Unless the water is picked up from another location as well, the book does not mention it.

I agree the best place to work on it or test it is on the water, but there comes a point where it becomes a hassle to try and get it to the water and mess with it.

I did not time it but would guess it ran a good thirty to forty seconds or more at high idle 1200 rpm. I would have thought that would have been enough time to prime itself.

I?ll try back flushing it tonight and see what happens

Thanks for the advice

 

[martyh]

Re: 4.3 heat issue

Here?s an update for ya.

I attached and clamped the garden hose directly to the hose that runs to the outdrive and removed the raw water pump on the outdrive. I turned on the faucet and water ran out freely. I reattached the raw water pump and than turned the hose on again, water flows freely from the pickup screen with four holes on the lower leg and two little pee holes I had not seen before. I plugged the lower holes of the pickup screen with my fingers and the water flow increased as well as the pressure. At this point, I am convinced that the lower leg water passage is not blocked or restricted.

With the lower portion of the outdrive submerged, and I am sure at this point that the outdrive is underwater enough because the holes that poured water when I back flushed are under water. I think back to when the boat is in the water and under power the top portion of the outdrive is not under water, so submersing the lower half in a tub simulates being on the water with the exception that the speed is missing to force water up the outdrive if that happens at all.

I reassembled everything leaving the thermostat hose disconnected and started it up again, and timed it this time. I ran the engine for 3 minutes, varying it in different rpm, slow or fast, in forward or reverse gears, and still nothing. I am guessing that it has to re-prime itself each time after taking it out of the water but cannot find any information that verifies this.

Can somebody tell me how soon the water is supposed to come up to the thermostat after starting the engine or does it need the movement of the boat in the water to force it up to the thermostat housing?

Any opinions, thoughts, ideas? What am I missing?

 

[danond]

Re: 4.3 heat issue

I changed the thermostat, one side of it was broke, the metal tab that holds the spring in place was gone. I am assuming it is in the engine water pump or it?s in the engine block somewhere.

Same thing happened to me; it's probably at the bottom of the big recirc hose. Remove it, I bet you find it in there.

 

[martyh]

Re: 4.3 heat issue

Same thing happened to me; it's probably at the bottom of the big recirc hose. Remove it, I bet you find it in there.

Funny you mention that, after calling it quits for the night on the raw water pump dilemma, I moved inside to the engine water pump. I removed the lower hose and the pump to look inside. I wanted to see what kinda shape it was in and see if the broken t-stat piece was there, and no such luck. I image it?s in the block somewhere. As small as it is I doubt it?s causing any harm. Thanks for the info though.

 

[Uraijit]

Re: 4.3 heat issue

Doesn't have to be very big to cause some major blockage. I had an overheat problem this week, with some silicone sealant that squeezed out and blocked part of the water pump passages on the engine block. Couldn't have been more than half a dime's size of blockage on each port, but it really made a HUGE difference.

The good news is, I flushed it so well, and got so much other junk out of the engine while trying to figure that out, that the engine now runs cooler than it ever did...

 

[Boatin Bob]

Re: 4.3 heat issue

I still don't think you have it low enough in the water to prime the pump. The pump is almost at the top of the drive and normally when in the lake the pump is pretty much under the water. The other thing to quickly check is the vent hose that attaches to the pump housing, can you blow through that or is it plugged?

 

[phillyc1]

Re: 4.3 heat issue

I think Im reading this right. When you pull the hose off the thermostat, no water when the lower unit is submerged. And you replaced the impeller. 2 things to consider, the raw water pump housing on the outdrive, is the cam inside worn out, or are their holes in the plastic housing. Also, the pickup tube between the upper and lower unit has 2 rubber gromets that can rot or the copper pipe can corrode and leak. My money is on the pickup tube gromets since you looked at the raw water pump. If the pump leaks, you can see water pouring out of it while she's running.

 

[martyh]

Re: 4.3 heat issue

Hey Bob,

I checked the vent hose while I had the raw water pump off. It?s not plugged, it blows freely. I hear ya on not having the outdrive submerged enough, but I question, how do people get away with running them just on the earmuffs? Unless the water being forced into the outdrive is enough to get it primed. Hmm, I?ll have to try the ear muffs too. I appreciate your suggestions and ideas.

Phillyc1
Yes, as you know, the hose going to the t-stat is what supplies water to the engine. The problem is that for some reason I can?t seem to get the water up to the t-stat.
I have verified that the pump shaft was turning when the engine was running, and the impellor will only go on one way, as it has a slotted notch verses a splined shaft as some use.
The only hole in the raw water pump plastic hosing is the vent hole for the vent hose. When I clamp the garden hose to the t-stat hose to back flush it, no water leaks inside the boat and the only water leaking outside is where it would get picked up from the outdrive. It?s also been a fresh water boat all its life, or so I was told by the guy I bought it from, so corrosion is minimal if any.

Also, I noticed that when I shut the garden hose off the water passage from the t-stat hose to the port on the raw water pump (with pump removed) will retain water until I remove the clamp on the garden hose (which breaks the seal) and then the water drains out of the port where the raw water pump would be. So, this tells me that it is a sealed passage otherwise it would drain prior to breaking the seal.

On another note, I had the outdrive off last summer to grease u-joints and etc, so the lower ?O? ring and gasket are new, and I may have mentioned in another post that the engine has ran hot or warmer than what I think is should since I got the boat a few years ago.

If pictures will help I have attached a couple. The picture shows the two ports, the left side goes up to the t-stat hose and the right side goes to the pickup screen in the lower leg.

Next step, I am gonna try using the ear muffs to force the water up, and then try back flushing while the engine is running to see if that primes the pump. If that don?t work, Bob, I am headed to the lake to submerge the whole outdrive.

On another note, can you guys touch the exhaust manifolds on yours when the engine is or has been running for awhile? I had a Bayliner with a closed cooling system a few years back and I could hold onto the exhaust manifold regardless of how long it had been running and I am wondering if this is suppose to be the same way.

 

[Dakota47]

Re: 4.3 heat issue

I have a 1987 OMC cobra , after running it for 30 minutes the exhaust manifolds are cool to the touch, they always stay cool.. it sounds like the impeller housing is not holding a good seal. you can replace all of it with new parts & seals.

 

[martyh]

Re: 4.3 heat issue

Okay, another update for ya.

To start off with, I am beginning to think I am chasing a ghost.

I put the ear muffs on the outdrive and the raw water pump pushes water up to the t-stat housing. Next, I reinstalled the outdrive hose to the t-stat housing and started the engine, and within a few seconds water started pouring onto the ground from the exhaust ports
which is normal.

I then watched the temp gauge climb to its normal location and stop. (See picture)
The last post I asked about the manifolds being hot because two weeks ago when I spent the day on the lake the engine was generating a lot of heat or what I thought was a lot of heat and the manifolds were hot to the touch.

Now, while running the engine, the manifolds are cool to the touch. The intake hose, and the two hoses going to the manifolds are also cool, the big hose off the engine water pump is hot but feels normal. I am beginning to question the accuracy of the gauge and sender.

Bob, thanks for pushing, my plan now is to take it to the lake tomorrow or Saturday night to see what happens.