PCM XR7 Coolant Reservoirs

[BickUW89]

I just bought a 2016 Nautique G23 a few weeks ago, and I'm going over it to familiarize myself with it and make sure it's ready to go on the water. I noticed that the engine has two coolant reservoirs on it. One of them is full of coolant, and the other is completely bone-dry empty. I'm new to boats, but not new to working on cars and trucks, and I've never seen a coolant system with two reservoirs.

Am I supposed to add coolant to the other reservoir that's empty, or is it just there as additional capacity for coolant while the engine is running? I asked the prior owner and he said he asked the same question when he got it, and was told it's supposed to be this way.

Any information or advice is appreciated!

[PrairieView]

Did you get a response on this question? I have a new-to-me 2014 G25 with the XR 550 and noticed the same thing on mine.

[Scooter G]

Is that a line stamped on your dry tank BickUW89, 1" up bottom right?
My ZZ8 runs one holding tank, same story, but no lines or tank indicators. I couldn't find anything out there on the matter, other than checking and purging the tanks, and all looked good there.
I added about an inch of 50/50 green, seems to not deviate from that level, although I keep forgetting to check it when its hot, that might tell a different story.

[BickUW89]

@PrairieView: I never did get a response on this post, and never could find anything on the internet.

A few weeks after I posted this, I got it out on a lake for the first time, and while puttering around I started getting exhaust overheating warnings. They would come and go, but I didn't stay out long. The next weekend I took it out to surf for the first time. For a while it ran OK, but I was watching the engine temperature and it kept creeping up to 210, and several times self-throttled back to avoid overheating. I took it straight to the local Nautique dealer and dropped it off for them to look it over.

The first thing they told me the next day, after their mechanic had a chance to look at it, was that there was no coolant in that reservoir, and very little coolant in that circuit. They told me it absolutely is supposed to have coolant in it. They also replaced the impeller and did a few other things. However, they never could pin down the overheating, because it kept happening to them in the shop, too. After racking up $3,000 in shop time, I told them to button it up and that I'd bring it home to figure it out.

Turns out the problem was that there is a second thermostat in the system, that controls coolant flow to the exhaust heat exchangers. That one is in a two-part aluminum cylinder spliced into the rubber hose going to the exhaust manifolds. It was supposed to just screw apart so you can quickly change the thermostat, but this thing was welded shut from rust. It took almost an hour, a few f-bombs, and some nicks in the finish from wrenching on it while I had it in a vice, but I finally got it apart.

OMG. The thermostat that was in there was completely rusted shut, and the hoses had lots of rust residue coating them. I posted a picture of the It must've been in that condition for years. I removed the thermostat, put it back together without it, and fired up the engine and voila! Overheating problem solved. All along, that was the problem with the overheating issue. I'm actually pretty annoyed that the dealer's mechanic didn't check that as one of the first things. I ended up putting a new thermostat in, and the boat is running perfectly now.

[BickUW89]

scooter G, there are two lines stamped on the reservoir. The lower one says "MIN", and the upper one just below the chine says "MAX." I attached the actual photo so you can zoom in on it.

[Scooter G]

Good write up BickUW89, and good to know.
After all that I assume you are running coolant over the minimum line. That is a little odd that the 2nd thermo wouldn't have been on the dealer's punch list, frustrating (and expensive), I hope that motivated a phone call. $3000 seems a little pricey for an impeller, coolant fill, & purge.