Honda radiator boil

My 93 Honda accord had radiator problems and leaks. I replaced the
thermostat and the radiator. it doesn't boilover anymore but I still can
hear that the water is boiling into the overflow container when I turn off
the car. when I turn off the car the fans stop... if I leave it for a few
minutes the fans turn back on. I have replaced the thermo with the
suggested value one. are the fans not turning on enough? is there an
electronic sensor that is turning on too high? shouldn't the water temp
stay below boil?

Thanks
Dave Packham

 

Replace the rad cap.

 

Pretty sure the new radiator came with one but ill check. Would that be
cause of the water getting to hot? Or is it that the cap is loosing pressure
and allowing it to overflow? Is the water temp always in the boiling range,
but just being contained?

Thanks

Dave P

 

It's certainly possible that at times the coolant temperature is well
above 212F... and you're absolutely right that it's the pressure that
keeps that boiling in check.

Professor
www.telstar-electronics.com

 

Yes, that's my thinking. It might be something else, but it's the cheapest,
simplest and most obvious thing to try first and you should to it
immediately, not tomorrow or the next day or the day after that.

If cap replacement does not fix the trouble, then you should suspect the
head gasket.

No, it's only /sometimes/ in the boiling range. Theoretically, it's always
supposed to be at 194F, the rating of the thermostat.

The combustion chamber runs at about 2,100F, but coolant flow and radiator
function are supposed to be such that the coolant itself does not get hot
enough to actually boil. The pressure imparted by the action of the rad cap
is supposed to retart boiling by holding the system to about 13-15 lbs.

Modern rad caps don't even hold pressure at all /until/ the fluid begins to
boil, at which point pressure builds rapidly and the cap seals, quelling
the boiling.

 

Hm, that's interesting and prompts me to ask a relevant question, too.
From what you are saying, it should be very rare that the radiotor fan
should kick in after stopping the engine because according to the specs
that fan should only come up if its sensor detects the coolant to be at
223 F, if I recall correctly. But I noticed that my car's fan kicks in
pretty regularly after I pull into my garage and stop the engine, even
if it was not an especially hot day or hard driving. I'm pretty sure my
thermostat works OK as it was just recently replaced with a new one. Is
this normal behavior from a '94 Accord LX? The car otherwise runs
great. I don't recall though that the original radiator cap was ever
replaced.

JP

 

The cooling fan will come on when the coolant temperature is between 191
and 197F. The thermostat is supposed to open at 194. Once it opens, the
temperature in the block falls rapidly.

The cooling fan will ALSO come on after shutdown if the OIL temperature is
above 226F. At least in the US. Canadian cars may or may not have such a
feature, depending.

 

Would a defective thermostat cause the cooling fan to *not* come on? I've
bypassed the thermoswitch to have the colling fan always on when the
engine's running (due to some overheating problems), but recently changed
out the thermostat so am curious if that could have been the problem all
along.

 

Yes, if it makes engine run too cool.