Coolant temp question

[SlowNeal]

Sounds like a dumb question, but I've noticed in my 95 GSR, that at wide open throttle the coolant temps seems to go down.
Also, when it's cool outside, if I engine brake down a long hill, the coolant temp will also fall. Is this normal? Is there any cause for concern?

[Stin1]

Change your thermostat. It is most likely sticking.

[coolhandluke]

How are temperatures being measured?

[SlowNeal]

I replaced the thermostat a few weeks ago, that was my thought, too.

Temperature is only being measured by the gauge on the dash.

Kinda like this... https://youtu.be/49XKVnCPcZk?t=129

However, mine tends to dip a bit further than is shown in the video.

[aw614]

Did you get a good bleed on the coolant after changing the thermostat? I don't think B series motors have bleeding issues like the K series or D17, but using the bleeding funnel does make things a lot easier

[SlowNeal]

ya'know..... now is the time to finally buy a coolant funnel. It's worth a shot.

I always assumed the coolant overflow would bleed the system passively, but I could be wrong.

[coolhandluke]

I replaced the thermostat a few weeks ago, that was my thought, too.

Temperature is only being measured by the gauge on the dash.

Kinda like this... https://youtu.be/49XKVnCPcZk?t=129

However, mine tends to dip a bit further than is shown in the video.

Thank you for the visual, this helps me better understand.

ya'know..... now is the time to finally buy a coolant funnel. It's worth a shot.

I always assumed the coolant overflow would bleed the system passively, but I could be wrong.

Oh this information helps as well. The coolant overflow will not bleed the system. I recommend a coolant bleeder setup and letting the car idle until the radiator fan kicks on ~2-3x. Not, the top radiator hose gets hot, so one may want to wear gloves to avoid risk of burning. I typically will squeeze the top radiator hose after the thermostat opens up.

Researching Amazon, this seems to be a highly rated and affordable kit:
https://www.amazon.com/OEMTOOLS-87009-N ... 73&sr=8-15

[SlowNeal]

Thanks for the info and advice, guys. Funnel is on the way, I'll report back with my findings.


FWIW, I also kinda think that the temp dropping on a downhill... could it just be that while engine braking, the engine really isn't producing much heat, and the heater core is doing an adequate job of over-cooling the system?

Also, in my head, at high RPM's the water pump is spinning fast enough to create enough flow to kinda push the thermostat open a bit.... for better or worse. lol you don't wanna be in my head

[coolhandluke]

Good topics, let's walk through these items:
-Heater core - This circulates heat from the block through the firewall to provide heat into the cabin. The temperature slider opens/closes via metal wire. The heater core's only function is to heat the cabin. When the coolant is low, that is why one's heat may not work well.
-Thermostat - Opens/closes bases off a mechanical temperature. That's why aftermarket thermostats open "sooner"- ie lower temperature threshold, or "later", via a higher temperature threshold. When closed, coolant is not circulating through the radiator, this is advantageous for (at least) two reasons. 1- enables the engine to come up to operating temperature, 2- Prevents external factors like cold weather/freeway driving/etc., from reducing the engine's temperature below operating range. The thermostat "opens" to allow coolant to flow to the radiator to reduce engine temperature in conjunction with the radiator fan. Honda thermostats fail closed, preventing the engine from overheating during failure, but possibly leading to scenarios like yours.

[SlowNeal]

I am aware how a heater core and a thermostat work....

Also, I've recently replaced the thermostat, kinda ruling that out as an issue.

So, on a cool day, with the heater up past halfway, and the fan speed set to "2"...... engine braking down a long hill. Say 70 mph for 30-45 seconds in 5th gear..... do you figure that the heater core (which is just a heat exchanger) could effectively cool the car in that scenario?

And while we're discussing thermostats, if they fail closed, the engine will overheat. If it fails open, the car will not heat up at all. And after thinking about it a bit more, (crazy person) in the scenario I dreamed up before, the water pump would actually be pulling suction on the thermostat, sucking it open, not pushing it open, am I right?