Vectortrex

iTrader: (1)

I'm not actually sure what's going on with this, but here we go anyway.

After shutting the car off, I've inherited the previous owner's habit of lifting the hood to help the bay air out faster.

What I've noticed is that sometimes I hear short bursts of "gurgling", like water is moving through the system. This sounds a lot like boiling coolant, but it only happens for about half a second, in 2-3 second intervals. It also sounds a lot more like air moving through the system, vs boiling. It's hard to source the sound, but the general area appears to be the top of the engine near the middle around where the throttle sits.

The temp gauge reads below half and I've never seen the overheat light come on, but I've read the stock gauge is fairly useless in this regard.

The car also has larger radiators, and an aftermarket AST. Coolant level reads over the 'F' on the dipstick. Coolant also appears to have a healthy green color, though I don't have the tools to check boiling/freezing point.

ArmAnirx7

iTrader: (24)

Try burping your coolant system.

Sgtblue

iTrader: (16)

What you describe is not uncommon, but suspect the localized boiling you're hearing is probably nearer the turbos...theyre water-cooled and likely the hottest at shut-down. It's not necessarily a sign of over-heating.
If the car is new to you I would install a decent aftermarket temp gauge asap and change the coolant. You can't always go by appearance and coolant goes acidic over time. That can be hard on soft seals. And you're right, the stock gauge isn't linear and absolutely worthless.
Check the 3rd Gen section FAQ for threads related to both.

TomU

iTrader: (11)

Get an aftermarket temp gauge. The stock one is worthless

Vectortrex

iTrader: (1)

Gauges ordered, will report back when I have more data. I'm also going to go over the fan relays and input just to make sure I'm not missing something obvious.

If I had to place the sound I'd say it's actually coming from the throttle body, but that seems incredibly unlikely so I'm going to just assume it's probably my ears playing tricks on me.

TomU

iTrader: (11)

Coolant does flow through the TB to warm intake on cold starts. You may have air entrapment. Use a Lisle funnel filled 1/3-1/2 way with the engine on to bleed the air

Lisle Corporation

Sgtblue

iTrader: (16)

If your car is still near-stock, there is a small coolant line that runs to the throttle-body for the Accelerated Warm-up System (AWS). I doubt it's the source of your noise but anything is possible I suppose. The AWS system was one of those stupid efforts to placate the emissions ***** and most guys remove it. I only mention it because the line is a convenient place to put the sensor for that temp gauge and yields accurate readings even before the t-stat opens.
More info here...(check Post #36 for list of fittings)...https://www.rx7club.com/3rd-generati...d-idea-392910/

As for the fan system, this might be of interest....
https://www.rx7club.com/3rd-generati...system-906142/

Vectortrex

iTrader: (1)

Yeah I'm digging through the FSM related to the cooling system right now.

The non-temp related behaviors (AC switch and the test wire in the diag port work per FSM) appear to work, but I'm finding it more difficult to bench test the temp related behaviors, so those might just have to wait until I have a reasonable idea what the operating temp is.

I was also going to bench test relay 3 (Thermoswitch relay) but I had to order some spades to crimp up since I can't get test leads in there safely with the rubber surround in the way

Of possible interest is my recent discovery that the intake is actually missing a part. There's supposed to be a plastic piece that goes between the intercooler cowl and the air box; this was included but not installed (It no longer fits as the aftermarket rad displaces the air box about 3/4 of an inch). I'm thinking it's probably safe to just cover this with some plastic, but I don't think this could cause much more than reduced intercooler efficiency.

Sgtblue

iTrader: (16)

Since you mentioned the thermoswitch input, you should know that a lot of us change out the stock version for a S5 FC thermoswitch. That changes threshold temperature for that input from 108 C. to 95 C. Not real critical this time of year but it isn't expensive and completely plug n play. And in the summer, it gives you that much more cushion.
If your radiator is displacing the air guide from the factory intercooler duct to the intake THAT much, then it's probably not installed correctly. Since it's probably not really driving season where your at, and especially if you change coolant, it might be a convenient time for you to pull things out and look into that.

Vectortrex

iTrader: (1)

Thermoswitch is on my list of things to do. I'm debating doing the fan mod as well but I'm hoping it'll end up unnecessary since Washington is pretty mild weather wise.

The part being displaced is the air filter box, not the intercooler cowl.

Sgtblue

iTrader: (16)

In the event it's helpful at all, I found an old picture of my aftermarket temp gauge sensor installed in that throttle-body coolant line. the nice thing about it is that it's so accessible, requires no drilling and readings are immediate and accurate. Although I removed AWS several years ago now, I still use the line for that gauge....

Vectortrex

iTrader: (1)

Update!

Gauges installed and the weather was nice enough for once to go on a quick run.

The engine itself appears fine. Only got up to 94C in traffic, 80ish when moving. After I shut it off, I shut off the engine, then put it back into RUN so I could monitor the gauges. Temp at the gauge (Throttle body) slowly went down and fans were off.

After about a minute, the temp was still slowly going down (high 80s at the point, parked at 92) but the noise started, and moment later the fans kicked on. So the residual heat issue looks to be likely. Might be time to do the 10 minute fan timer mod.

Sgtblue

iTrader: (16)

That will not effect coolant temperature. The coolant isn't circulating. Probably just air in the system.