Another Overheating Issue @ Idle

[cyauch]

I've spent the last week reading, reading, and doing more reading, trying to logically figure out where to start. Short story: overheats at idle. Gauge pegs out and alarm goes off. Engine shuts off around 180*. When on plane, or RPM's up, gauge fluctuates but never reaches the 175 mark. low reading on gauge (basically 'cold' is 125* and the first tick mark i'm guessing is around 140 or so. 175 is straight up on the gauge. mention all that for reference.

Included pic of all serial numbers of engine (5.0 GXI-E), drive, etc.

Short history: new to me last spring. new it needed a little work, but ran great for three months. then intermittent over heat. noticed more often after a beach at a river sand bar, but just wasn't consistent. then, underwater strike that killed rest of season. I have another thread on here on all the work done there (thanks to everyone there for the info and help to this VP noob!) Able to do sea trials early Dec and no transom seal leak so good there, but fuel cell died. Fast forward to last week and installed new fuel cell / pump from Man in Michigan (thanks!). No more stalling when throttle applied. so all is good there now. But, noticed during last weeks trials while it ran great, temp spiked and alarm went off. waited a while, then ran it again to see if was also overheating at WOT. Nope. stayed cool as a cumcumber....until i hit the dock to trailer it.

So...I plan on buying the items needed tomorrow to run through the Diagnosis steps DonS has made avail. But for now, i've done the following:
- Impeller replaced last fall while engine was out. Inspected housing and saw / felt no scoring.
- Pulled thermostat tonight. While rust in housing, the build up was minimal. Including pics below. I was told this was 100% lake used and based on what i'm seeing in terms of build up, i'm thinking while possible, blocked passages may not be the issue. but not ruling it out.
- mans and riser i assume are original. and yes, i do plan on replacing at some point, but funds are tight due to covid issues this past year. But again, while they may be rusted, given no major build up in the thermostat housing, my hunch is maybe the mans / risers aren't the main cause. again, yes, i do plan on replacing in the near future. The underwater strike also tapped my budget for things i wanted to work on this winter

As you can also see from the pic, the thermostat i pulled looks like poo. But....dropped it in a pot of boiling water and it opened. compared to the new thermostat, there was about an 1/8th in gap difference, but both seemed to have a pretty big opening. I was hoping it was stuck. and maybe it was but knocking things around and trying to get it out of the housing may be made it unstuck. Will know for sure when i drop it back to test that change.

So my thinking so far is because temps normal at WOT but hot at idle, there's an obstruction and / or suction issue? My hope is once i install the clear hoses per the Diagnosis pdf that will give some insight. But any thoughts, hints, or suggestions are welcome.

Boat is a 2005 Regal.
Edit: The pic with the shiny thermostat is the new one installed.
Edit: Other observations i noticed when i pulled the thermostat housing:
- big hose to circ pump on front of engine loaded with water (which i expected)
- small host to fuel pump / cell had a little water in it
- all other hoses i took off seemed dry. at least no water went flying out as they came off. not even a drip from any of them. looked inside the hoses and they didn't even look wet at all. Dunno if that's 'normal'. possible the circ pump is bad? from what i've read while possible, most have stated highly improbable but I dunno.

 

[alldodge]

I think your sucking air or there is a restriction
Get a piece of clear hose at the hardware store and place it between the seawater pump and thermostat housing

 

[kenny nunez]

Look very closely in the thermostat housing for a metered “by pass” port, I have encountered a plugged port that caused what you are describing.
Do not overlook the circulating pump. Remove it and pull the cover, check that the impeller is not loose on the shaft and of course the condition of the blades.

 

[BRICH1260]

I`d pull the impeller and check it for damage. Does the engine behave the same way just running it from the blue flush port as opposed to running on muffs or in the water? Make sure the blue cap is put on tightly.

 

[cyauch]

Thanks! First - Yep, some other notes i didn't mention in the first post about things i checked:
- made sure plastic nipple in outdrive wasn't cracked, broke, etc. when i pulled everything to replace the transom seal after underwater strike. it was in good shape.
- made sure the blue cap was tight

Plan is to head to the store this afternoon and get the clear hose and fittings to rig everything up per the Overheating Diagnosis pdf I found from DonS. I hated making the post without having done that first, but figured i might as well start getting input sooner rather than later.

- 'metered' bypass port: is one of the hoses i removed attached to that or is internal to the housing? I ask because looking at each hose connection into the housing, they look pretty good. I see some passages inside the housing itself and using a small inspection mirror on a stick, they seem the same (again, aside from the minimal scale / rust build up on the walls). Basically, everything looks wide open internally.

- circ pump: i was debating last night about pulling and inspecting, but it sounds like that's not a bad idea anyway. i know some have said low probability, but with my luck, it's not gonna hurt to check it.

- RW impeller: while i was down there, yea, i'm gonna re-check that even though replaced in last Fall.

Final question about backwash / flush: i made sure the blue cap to the flush tube was tight. My next step was to stick a garden hose in the top hose of the RW pump in to blow out, if anything, in the oil cooler behind the engine. Do i need to disconnect the hose from the top of the oil cooler it or can i let it blow straight out the foot ports?

 

[cyauch]

I`d pull the impeller and check it for damage. Does the engine behave the same way just running it from the blue flush port as opposed to running on muffs or in the water? Make sure the blue cap is put on tightly.

I kinda jumped the gun on this one. I pulled the t-stat housing first. I'm a little confused on the the various posts about using that for overheat checks. The common consensus is idle rpm's only (which is fine, that's when it overheats ) but i see different opinions about what it proves or disproves? I mean, looking at the parts diagram and cooling flow diagrams, assuming i don't get an overheat using the blue flush port, then logic says oil cooler obstruction or something prior to that (hose, nipple, foot intakes, etc) right?

But yes, i do plan on doing the flush port first. Then the muffs.

 

[cyauch]

Uggh. Just noticed putting the gasket for the t-stat housing to block surfaces as a tear in it!! crap. Looks like i'll be delayed in getting that back on now.

 

[BRICH1260]

I`d run it at idle from the blue port and see if it still overheats. If not, then you know your problem is between the drive pick up and the pump, possibly a clog. If it still overheats, then you know your problem is in the front of the engine

 

[cyauch]

I`d run it at idle from the blue port and see if it still overheats. If not, then you know your problem is between the drive pick up and the pump, possibly a clog. If it still overheats, then you know your problem is in the front of the engine

roger that. thanks. found a marine place that has the t-stat housing gasket as well as the two gaskets for the circ pump. Picking those up as well as the clear hose and fittings. Hope be to able to get it all back together by sometime this weekend and do the idle test via the flush port.

 

[dypcdiver]

See my post ref. the Bronze tube that joins the upper and lower outdrive parts. https://forums.iboats.com/threads/overheating-after-impeller-change.743108/

 

[cyauch]

See my post ref. the Bronze tube that joins the upper and lower outdrive parts. https://forums.iboats.com/threads/overheating-after-impeller-change.743108/

Thanks. Yep, been following that thread, and have read in a couple threads here and elsewhere about that tube. I believe it's #12 here: Lower Unit Parts Diagram

I also see there's a 1" extension kit that has a similar part, but different number. Don't believe I have the 1" extension kit based on the diagrams themselves. how do i determine if i have that? Can it be determined based on the serial numbers in my first post?

Last night i was able to get the clear hoses on and the t-stat housing back together. However, i did not take the circ pump off to inspect yet. Their computer said they had a pack of two in stock but alas, the bin was empty. They are ordered but won't receive till next week.

No matter, I'm going first backflush for a little bit, then connect water to the flush tube and run it for a bit and see what happens. I tend to think something is clogged up and / or possibly that tube in the foot. Like i said in first post, things seemed to be fine (now questioning myself) until we beached on a sand bar last year. that's when i noticed intermittent overheat at idle. this year its constant. could be a coincidence or my OCD getting out of hand. Retired military (SeaBee) so i tend to be anal about meters, gauges, etc. and their readings. I did, however, also check last night the hoses an each side of the transom, and the connection to the oil cooler just to make sure i didn't leave one of those loose.

Hopefully I'll have a better idea of where to focus in a couple hours. Thanks!

 

[cyauch]

typing from my phone so ignore my typos . so going on 40 minutes at idle. temp seems to be holding steady at around 150-ish. i saw it hit that temp then drop to 125 them slowly climb back up to where its at now around the 10 minute mark. i have clear hoses in place and hooked up to the blue flush port. not seeing any bubbles but then again it is 60 psi well water.

going to stop and change to muffs and see how that goes. i have some videos also bit have to figure how to post those.

also, before using the port i flushed the supply side to RWP with my home made fitting

 

[cyauch]

ok, think i can link to the videos.

flush port engine not running

flush port engine running

 

[cyauch]

Well that didn't take long. Put the muffs on and bam! hit 175 quick then alarmed and shutdown. Course, i may just have a crappy set of muffs. very stiff rubber and water is going all over the place. i'm willing to bet there's not enough pressure to overcome the height / distance to the RWP. And seem to remember having issues with these muffs before

 

[bruceb58]

What muffs are you using? Turning the water on full I hope?

Correct me if I am wrong but the Blue flush port is after the impeller. There should be no water going out your drive inputs when using the flush port. You need to pull your impeller.

 

[cyauch]

What muffs are you using? Turning the water on full I hope?

Correct me if I am wrong but the Blue flush port is after the impeller. There should be no water going out your drive inputs when using the flush port. You need to pull your impeller.

Thanks

But my impression from the VP manuals / diagrams, the port is before the impeller so that water is flushed back down to the drive as well as into the circ pump, engine passages, etc. If this isn't correct can someone tell me the correct sea water flow? On the flush port i also got water out the exhaust. nothing on the muffs.

As for the muffs, well, they are crap to say the least. Probably 15 years old and the rubber is as hard as a jon on two-dollar-trick-for-a-dollar day. There is a crap ton of water getting sprayed out.

 

[alldodge]

I would remove the pump cover and look at the impeller

 

[cyauch]

I would remove the pump cover and look at the impeller

Thanks. I'm gonna do that this week. Reading another thread that's active about someone having a very similar issue, and it seems are symptoms are very very similar. I guess it's quite possible i screwed up installing the impeller last fall. I'm also keeping the possibility of the copper tube in the lower unit as the culprit also.

I've been away for kids travel soccer, so today was the first time i've been able to do trials since i replaced the t-stat. My hope was that after that AND backflushing the suction side of the RWP all would be ok. On the blue flush port she ran cool as a cucumber for a hour. Today? No so much. notice at cruise temps were around 160-ish. But when at idle, 180-ish and engine shutdown. No alarms though.

Observations today:
- Risers very cool to the touch when overheat happened. I expected to scald hand but was able to hold on top of risers with no real discomfort
- Clear hoses on RWP: saw no visible air bubbles at idle or when crusing. RPM gauge broke but was going about 30 MPH
- Not in gear: if I gave the throttle a little bump, i would notice a sizeable air pocket in both suction and discharge of RWP, but it would quickly go away and turn to a solid stream of water.
- See attached pic. Prior to t-stat opening, i could see water in these two clear hoses. Not a steady stream, but there was some flow. However, once up to operating temp, i noticed no more flow throw these two hoses. Can someone explain how water flows when cold / hot? I see the diagram, and logic tells me whether t-stat opened or closed, water should be flowing.

So my plan of action is to replace the impeller. In fact, I'm just gonna go ahead and replace the RWP entirely. it's 15 years old anyway, and have no clue what's been done to it prior.

IF that doesn't resolve the issue, then i think my next step is to pull the lower unit and inspect that copper pipe.

Ideas?

FYI: The impeller i installed last Fall as PN 21959348 from Cecil Marine. Is that the correct PN for my serial number?

 

[bruceb58]

You should really have the clear hose in the hose coming from the pump but I guess what you have would work.

 

[dypcdiver]

When I did these tests, I had installed a new Original Volvo Penta raw water pump. These might give you a clue. Tests done before finding the cause was the Bronze tube.