Honda thermostat fail - coolant fault?

dublo, Jul 16, 11:52am
Our '99 V6 Accord's thermostat recently failed (very slow warm-up due to a perished seal.) Our WoF garage man said buy a genuine Honda replacement rather than an after-market one, but he also said he had had similar failures with a Honda he owned some time ago.
When I flushed and refilled the cooling system 2 years ago I used the same R*p*o Antifreeze/Antiboil 3-year life concentrate diluted 50% (suitable, it says on the label, for V-series Commodores) and which our garage man said was fine for the Accord, because I was too tight-ar*sed to lash out on genuine Honda coolant.
Now, I wonder if that coolant in our car, and the Honda which he had owned, had affected the thermostats' seals?

djrandomguy, Jul 16, 12:30pm
99 was a while ago and it's most likely that the seal perished or that the thermostat itself was stuck and you were getting slow warm up due to water only flowing past the 'jiggle pin' safety hole. Having a blocked thermostat would have placed more pressure on the seal too. As long as there is no lasting damage, count yourself lucky.

a.woodrow, Jul 16, 1:28pm
I would say failure after 19 years is fair wear and tear?

pumpedfaty, Jul 16, 1:43pm
Yep that a good run, cant moan at that. Ive had thermostats Fail after 2 years, an original part. Bit like Rusian roulette, just wen u think its all good.
And sum times it can be the cylhead and or gasget letting go, keep an eye on it. Get the radiator flushed, flow very important.

intrade, Jul 16, 2:28pm
well use the factory cooling fluid this way you can rule that out to be a problem.
Vw have had rotting plastic on there g11 blue coolants . they have now watrning signs like G12 on cooing bottles to not use anything but geniuen G12 or higher spec coolant.
General motor cars use dexcool it makes mud when it fails.

scuba, Jul 16, 2:48pm
If the thermostat was blocked or stuck shut it would have overheated.

dublo, Jul 16, 2:55pm
No, the thermostat was not stuck (open or closed), The perished closing seal just let the cold coolant past! Once the engine did warm up the needle on the gauge sat rock steady on the 1/3 mark.
(yes, Mr Intrade, I will buy genuine Honda coolant next time!)

djrandomguy, Jul 16, 5:19pm
Depends on the car, we had our TU powered Citroen with a broken [new] thermostat and it ran hot but didn't overheat completely. We had replaced the radiator and did the thermostat too as a precaution, unfortunate for us the thermostat was faulty from new and wouldn't open, but did have the 'jiggle' pin hole. We took it back as it was running too hot and the fans were always on, mechanic rang, apologized and did the job again with a new part at cost to the supplier. So blocked with debris/rust I'd agree, but this was with fresh coolant and it just ran at 3/4 all the time. Very strong engines the basic TU, so I wouldn't say every car could deal with it. Some can. I'm not advocating it, just so you know.

budgel, Jul 17, 6:02am
A lot of cars now have thermostats that stay open if they fail. My Audi 1.8TQ
wouldnt warm up all the way to Hampton Downs in winter. A few fast laps managed to do it though.

curlcrown, Jul 17, 2:25pm
A thermostat that failed after almost 20 years, must have been the coolant.

marte, Jul 17, 3:20pm
Audi G12 & 13 is Glycerine not Glycol from what I have read.
And always check the new thermostat by putting it in cold water on the stove & bringing it up to a boil while checkinging the temp.
Use antifreeze to lubricate to rubber seal on the thermostat.

audi_s_ate, Jul 18, 7:08am
My experience with the many honda's that I have had is that the life expectancy of the original thermostat is approx 20 years - I've replaced 4 in the ones I've owned all about that time frame - it's about an hours labour and $39 from Honda for a genuine replacement. The fuel savings in the first couple of tanks will pay for it.

dublo, Jul 18, 8:17am
Thanks, audi-s-ate. Yes, this car 19 years old so sounds about right. Honda thermostats are now $49-95, 1/2 hour labour to fit (just too fiddly for my older and slightly less nimble fingers to get at the rear mounting bolt on this V6 engine!
We realised it had failed to seal closed at the onset of winter - 4 to 5 km warm up time, during which time the auto box would stay in 3rd gear at town speeds.
I understand late model V6 Commodore thermostats are on the rear of the engine and under the bulkhead, and require removal of the inlet manifold to get at them, at considerable expense, so thankful for a (relatively) accessible engine!

poppy62, Jul 18, 8:31am
"Discerning people buy Hondas!"
our '99 Accord V6, which I call our Japanese Rolls-Royce (great engineering!

Rolls -Royce weren't noted for their reliability either, regardless of the engineering standards.

dublo, Nov 20, 11:10am
Agreed, and you can buy a Shadow or Spirit for not many thousands of dollars, but that can just be the deposit! They have very complex electrical and hydraulic systems. (I would still like an older, 6-cylinder one!)