Overheating Issue

[MarkVon]

Update

I took the end cap off the heat exchanger and took a picture of the inside. Looks all clear (see pic below).

I also took the hose off the heat exchanger that was coming from the exhaust manifold and filmed it while turning the engine over. Looks like there is good flow and the coolant is clean:

https://youtu.be/vVDL5coInlM

When I warmed up the engine, the hottest part to touch was the head on the opposite side of the thermostat housing (where I’m pointing in pic below).

My next step will be to remove the thermostat housing and see if there is a thermostat that is stuck but I need to get some gasket material first so I can put it back together.

The other thing I’d like to do is get a heat temperature gun and compare the temperature of the engine to the gauge reading in the cockpit.

[Surcouf]

great first step. You have now established that coolant flows from the coolant tank back up to the Heat exchanger, so proved that coolant pump is pumping, and that there is no plugage in hoses etc....

Now to rule out potential issue with the thermostat without a gasket: do you have a valve between the water jacket plate and the thermostat housing (see picture below)? If yes close it, it will prevent water from by-passing the block, forcing all water through it. Try to run your engine again.
- If it does not overheat anymore, your thermostat is the culprit.
- If it still overheats, you need to rule out an (unlikely) potential plugage of the thermostat on the block side. For that just repeat (once coolant cold) your discharge test with the valve closed or small line plugged.
If you do not have that valve, see if there is a way to remove the small hose where valve could be and plug everything (note: It seems that your access there is poor, and the hose being very short; it is somewhat difficult to remove that small hose without removing the thermostat housing). If you are just waiting for a gasket for the thermostat housing, you can just cut that hose to remove it and install a longer one on a temporary basis

[Surcouf]

and:
- your heat exchanger is very clean. So you should be able to rule out that one
- the "hot spot" you are pointing at looks normal to me, but I do not have much experience tracking hot spots on blocks

[Dave Neptune]

Mark, you can pull a hose of the housing and poke inside to feel for a t-stat. That looks like it may be an aftermarket housing, if so it may not of been designed for the A-4 style (bypass) t-stat.
It is not to uncommon for the A-4 style t-stat to get fouled or stuck with debris.

Dave Neptune

[ronstory]

Do you have access to an IR gun? Once you check the calibration by boiling water and verifying the temp is close... then shoot sensor and thermostat housing.

I have this one:

https://www.amazon.com/dp/B01BV0YMH4/ref=twister_B07RBXJ182?_encoding=UTF8&psc=1

... and I did find it humorous there was a flock of recent bad review of folks trying to use it to measure for body temp. With useful range of of -58F to 1000F+ they were complaining it was off 1.5-2 degrees at body temp range.

[tenders]

The photo in the Amazon listing stating "NOT FOR HUMAN" is also pretty funny: cheerful guy with laser focused on his head. Hey, we've all been there.

(I have the Harbor Freight version.)

[MarkVon]

I borrowed a heat gun and did a test on the warmed up low idle engine in the two spots in the picture below (under the green thermostat housing cover). 135F and 110F.

I’ve also attached a pic of the gauge. 30F difference! Maybe the engine isn’t over heating. Looks like I should order a new temperature output and gauge.

[ronstory]

And since you are FWC, if you ever get to 180+ degs, I would expect the vented cap to push out a bit of coolant. Unless you have a high pressure cap on it.

I have the Indigo thermostat with the 180F option and my little A4 one warmed up runs just over 180 pretty much all the time.

[MarkVon]

Thanks for the support everyone! I also spoke with Ken at Moyer Marine and he was so patient and supportive in helping me understand these issues and how best to move forward.

It looks like the issue was a malfunctioning guage (phew!). I ended up ordering the parts I listed above and will install them in a couple weeks.

[Ando]

I have the same exact gauge and I also have high temps
Although I have a replacement gauge, I will be holding off from installing it as I have a few steps to take before that, including fine tuning the timing and an acid flush of the cooling system.

[sastanley]

ken is always patient..another reason we love the Moyer crew. The IR temp gun is a great tool to help diagnose these issues...and another welcome..even though I am several posts late!

[Boat]

are we sure he is overheating? mine runs at 180

[MarkVon]

I just went for a cruise testing the engine temperature with the heat gun at 30 mins of 5 kts. The engine temperature didn’t get above 170F, but the gauge was 15-40F higher.

I’ll put in a 150F thermostat, new temp sending unit, and gauge when the parts arrive in 2 weeks. Hopefully problem solved. I’ll report the results.

[ronstory]

IMO, if you have fresh water cooling... get a 180F thermostat. You can run the engine at a temperature it prefers to run at vs. the cost saving compromise of a raw water cooled engine.

Minus the corrosion potential... of course.

[MarkVon]

I replaced the temperature sender and the gauge. The first test I did at lower (not lowest) rpms, sitting on the mooring ball, showed the gauge matching a thermostat gun reading (128) just below the thermostat housing.

However, I also used the thermo gun to measure other spots on the head and got 186 at the in the point in the picture below.

Is this normal? Or do I need to consider other things?