The problem:

Engine temp climbs at idle or when A/C is on...

- Only occurs on hot days, city driving or long high way drive with AC on.
- On cold days gauge hits operatuing temp and stays there and the heater works amazing
- Temp drops when driving, or when the heat is on high, or if I rev the engine in neutral

What I know:

- Coolant level okay
- No leak that I can see
- Replaced rad Cap
- Fans both come on (not sure if they come on at the right times)
- Fans don't run after key is removed no matter how hot the gauge reads.
- Fan control modual checks out okay
- When engine heats up Both rad hoses are hot and firm
- no cooling system fuses are blown
- I've jumpered both ECT A and B the fans come on the way they should be the engine on/off
- Fan relays work ( this is an assumtion based on jumpering the switches)

What I think:

- I suspect It's the Oil temperature Switch (V6) it has the same specs and function as the ECT B (I4)
- I know alot of peopple have said thermostat but I'm not so sure

What I'd like to know:

I know the ECT B and the Oil temp switch have the spec as far as opening temp, elec connecter etc. but are the parts interchangable are the threads the same. I ask b/c when I went to the honda parts counter at my local dealer he wasn't sure about what i was talking about so if I can use the b switch I will.


Any other thoughts, or anyone with a similar experience ( and hopefully a resoution )?

 

If the cooling system is working OK (as it appears to be from what you stated) it could be your temp sensor for the guage. It could also be your t-stat not opening fully

 

I had a 94 civic do the EXACT same thing... Once it climbed up to just below redline it suddenly started dropping quite a bit and then sometimes it would go back up sometimes it wouldn't.... it could be your water pump too... is there any strange noise coming from the engine bay? on my civic it was simply a thermostat but after reading your notes it could be a waterpump with broken splines.... first thing I'd do is spend the $6.00 on a new thermostat and see if that fixes it...

Something else: based on the fact that you said when you rev the engine in neutral it goes down I'm almost leaning towards the water pump being the issue. If it is replace the timing belt at the same time... but first off replace the thermostat

 

no strange noises coming from the engine bay. The engine was just put in a coupe of months back and the mechanics "said" he checked the water pump and said it was okay. Not sure I trust him but If changing the tstat and the oils temp switch and no luck I might look at the pump. Thanks

 

here's something to try (yes I realize it won't make a lot of sense in hot weather...) but anyway, start up the car on a hot day and let it idle, crank on the heater full bore and feel it, watch the temp guage, if it never goes above regular operating temperature and the incoming air gets hotter then your thermostat is opening and allowing the hot fluid into your heater core... that means that your heater core is now acting as almost a second radiator and helping cool things down so that would point towards the water pump... if the temperature climbs and the air doesn't heat up past just the outside temp then all of the sudden your temp gauge starts going down and the incoming heat gets hotter that says it's a thermostat...

Give that a try if possible

 

I suspect the problem is your thermostat that is sticking partially closed. Sometimes they will stick and other times they work. There are some thermostats being made today that fail open. I don't know how they manage to do that. To me, they look the same in design.

Another problem may be that your cooling system is very dirty and the small water holes in the head gasket are plugged. When you take the thermostat out then I would clean the system (and without the thermostat being installed in the engine -- gets a lot higher flow of coolant through the system).

I try to change my coolant every two or at the most three years and I always give the system a good cleaning. The radiator of our 1987 Chev. Celebrity with 251K miles still has a very clean radiator. And it is the original radiator. My radiators last forever due to the cleaning plus the fact that I put 7 lb. caps on the radiator.

 

Problem solved. Turns out it was the t-stat not fully openig, replaced it with the Genuine Honda part. A week later (a very,very hot week to boot) The temp gauge hasn't moved a stich past were it should be.

Thanks alot for your input.... one less thing to worry about!