Running Cold

[NSX-SA]

I have a curly one for everyone. The nsx has been taking longer to warm up to normal operating temperature at late to the point a couple of weeks ago on a drive the temp was so low it was in warm up mode and raised the idle rpm as if I just started it. A simular thing happened a couple of years ago, the thermostat shat it self and was jammed open. Thinking this happened again I remove the thermostat but found and tested it to be working fine. I replaced it with a new one anyway but still have the same problem. If I let the engine idle long enough the temp will rise slightly however if I go for a drive it drops to cold almost immediately. I haven’t checked the sender or temp gauge as yet but I don’t think that is where the problem is.



Any thoughts.

 

[ftuhy]

I had a "stuck-open" original thermostat on my '96 a few years ago. However, it was only partially open, so after 10 miles of highway driving, it would reach normal operating temperature and stay there.

The problem is the over-the-top Honda design. There's a rubber O-ring around the moving disc that can "mushroom" off part of the disc, preventing the thermostat from fully closing. This is a known, somewhat common failure.

If that is your problem again, the fix is simple. Buy a non-Honda thermostat from the local parts store. They are identical with the exception of that extra O-ring. Its just the simpler, more reliable, metal-on-metal design used for the last 100 years in just about every other car in the world. (The extra O-ring should not to be confused with the O-ring that goes around the entire thermostat to act as a gasket for the theromstat housing. The thermostat housing gasket should come with the replacement thermostat.)

The "generic" replacement fixed my problem, as the car now reliably warms up in under 5 minutes, depending on the outside temperature. Its the only non-OEM part on my NSX's drivetrain.

 

[NSX-SA]

Thanks for your reply and thoughts.

I just find it a bit unusual that i tested the old thermostat to be working fine and that putting a new thermostat - oem - i have the exact same symptoms.

 

[ftuhy]

Ooops. I somehow missed the point that the symptoms came back immediately with the new thermostat - my bad.

First, be sure there are no air bubbles in the system and that the coolant level is not low. Check at all the bleeders.

The next thing, I would check the temperature sending unit (on the same pipe/assembly as the thermostat housing). For '95/'96, the ETM says the sensor should measure 142 Ohms at 56C/133F and 49 to 32 Ohms at 85 to 100C (185-212F). So, roughly speaking, in the normal operating temperature range that's 1 Ohm change per 1 degree C. Based on how steady my gage is from local to highway driving, my WAG is you shouldn't see more than about a
5 Ohm change.

It would be reasonably easy to disconnect the lead at the sensor, connect up an Ohmmeter to the sensor & ground (at the sensor body) with the leads going into the passenger compartment. Then go for a ride and take readings. If the readings are steady, its the temperature gage. If its something in the dashboard affecting the temperature gage, such as a bad ground, it usually would affect all the gages.

As part of the above, make sure the electrical connector and the sender contact itself are clean and making good contact.

A remote possibility - but you would notice that - is the heater is stuck fully open, dumping all the heat into the passenger compartment.

Let us know what you find.