Radiator coolant and thermostat

How often I need to replace the thermostat?
Also, Haynes says to drain the coolant, unscrew the bolt under the radiator
and then disconnect the lower radiator hose. Is that correct? just by
disconnecting the lower hose will drain all the coolant including the block?
I do not want to mess with the bolt on the block, I heard is a PITA.
Thanks

 

It would help if we knew what kind of car you have (and please, be VERY
specific...this is an international newgroup)

 

Yes, I am sorry, I forgot. It is a 98 civic auto, 110k miles on it. The
thermostat, water pump and coolant was replaced at 80K miles or so with the
timing belt.
One time I tried to drain the coolant by just unscrewing the plug under the
radiator but not much coolant came out, this time I'd like to do it right.
If I run the hose thru the upper radiator hose, will I be able to drain all
that water? The new antifreeze from honda is already diluted.
Thanks

 

You don't need to remove the bottom radiator hose. Just remove the bottom
screw on the radiator and everything will pour out. The block won't be
flushed this way. You have to use a hose with water to flush all the coolant
out. Simply plug the hose in the radiator (by radiator cap) and if you
haven't disconnected the bottom radiator hose the coolant will be flushed
through the top radiator hose. So make sure you have some place to store all
that coolant+water.

I changed the thermostat for the first time at 100K on my 98 accord. It's
not expensive so if you can DIY then I'd replace it at 60K then 100K then
150/200K etc. I haven't looked at the manual but it's not that often. I
think it says it needs to be changed at 100K or so. Maybe someone confirm
this or I'll look tonight in my owner's manual.

Btw, what kind of car do you have?

--Viktor

 

Sam,

You have to open the coolant reservour (plastic bottle) and remove the
radiator cap in order for air to get in so the coolant can go out. The
principle is simple. Imagine you have a glass of water and a straw. You pull
some water in the straw and while you are holding the top closed (no air can
get in) the water stays even if the bottom of the straw is facing the ground
(analogous to radiator screw on bottom remove and radiator cap still on--no
air can get in and there's vacuum). Same way if you remove your finger or
tongue from the top of the straw air gets in, and the water drops on the
floor (analogous to removing the caps from the radiator and plastic coolant
reservour).

You can flush the block through the upper radiator hose only if the lower
radiator hose is disconnect (that's where the coolant will get out from the
block). Otherwise, if the bottom radiator hose is not remove, the coolant
will stop dripping from the top of the radiator (by radiator cap) and you
don't want that. There are a lot of electric circuits there (headlights,
horn, fans, etc.) and that's just one of the reasons. You'll make a big mess
inside the engine compartment if you let the coolant drop from top of
radiator hose.

Best if you remove top radiator hose and flush the system through top
radiator opening with the lower radiator hose intact, so the coolant will
come out the upper radiator hose and you can extend that to the bottom of
the car or to the side.

--Viktor

 

FWIW, my Chilton's manual covers 1984-1995 Civics and gives the following steps
to replace the thermostat:
1. Disconnect the negative battery cable.
2. Drain the cooling system (see owner's manual). Like you say, skip the engine
block bolt (more below).
3. Disconnect the radiator hose from the thermostat housing outlet.
4. Remove the thermostat housing outlet and remove the thermostat.
5. Installation is the reverse of the above, except use new gasket and O-rings.
Install the thermostat with the pin towards the thermostat housing outlet.
Tighten the housing outlet bolts to 9 ft-lbs. (84-91 models), and tighten
housing bolts for 92-95 models to 7 ft-lbs.
6. Fill and bleed the cooling system (again, see the owner's manual).

A picture that is supposed to indicate how to replace the thermostat of a 95
(and surrounding years?) Civic appears at
http://www.honda.co.uk/owner/CivicManual/pdf/10-7.pdf

I have skipped the bolt in the block for the last few radiator coolant drain and
fills. My recollection is most people here will say they did the same, because
you're right. It's a pain.

I do pretty thoroughly flush the system, though.

How much coolant your radiator system is supposed to hold; how to drain the
coolant; and how often to replace the coolant should be in your owner's manual.
For my 1991 Civic, the coolant is supposed to be replaced every 2 years or 30k
miles.

I've never replaced the thermostat. My Civic has 151k miles on it.

 

"electricked" <no_emails_please> spake unto the masses in

You cannot flush AND DRAIN the block that way. There is NO need to
disconnect ANY hoses.

To drain the block, which contains about a quart of fluid, you need to
remove the block drain. The block drain is not that big of a deal unless
it's never been touched for ten years. A 3 ft. cheater bar on your 6-point
socket will usually do it.

If you flush the system with water and fail to drain the block, your new
coolant will be very much diluted, leading to potential overheating,
freezing and corrosion.

Also, you must turn the heater full-warm so it will drain as well.

 

If you "flushed" the system but did not remove the block drain, your
coolant is understrength.

Have you measured its strength using a coolant tester? You may be surprised
how weak it is. The block holds almost a quart of fluid.

The longer you skip the block drain, the harder it will be to crack it
loose.

Eventually you'll have poor heater output and will fail emissions due to an
old thermostat.

 

I estimated how much the block held and diluted accordingly. I forgot what I
did, only that it involved several calculations. If anyone wants to know, I'll
dig out my notes and repeat them here.

But you're right to mention it.

snip

Thanks for the tip. I'll start investigating replacement of the thermostat.

But how do you get to poor emissions from a failing thermostat? Improper
cylinder temperature or something?

 

How do you keep from making a mess when you drain the coolant from the drain
block? I also agree is a pain.
How about draining and refilling the radiator with water several times until
the water you get is coolant free (of course, run the engine for a few
minutes to get the coolant inside the heater moving before draining it
again). Once the water is clean, drain it again and fill up 50% of the total
capacity with concentrated antifreeze, then fill up the rest with water to
get the right mixture.

 

Honestly - if it's been done correctly, one doesn't need to flush the
system. If you're using Honda Type 2 coolant, you won't be able to
bring up the glycol concentration when there's only water in the
system. If you're switching over coolant types, then it might be a
good idea - I did with a couple of "incorrect" coolants I used.
Flushing the radiator itself isn't a bad idea.

As for how to avoid making a mess - it can't be avoided. However -
it's helpful to have a really wide collection pan. I use the lid
from a 29 gallon Rubbermaid tote box. It's about 3X2ft, and if
positioned correctly will catch the vast majority of coolant from
the engine block. It's shallow, so I have to drag it out slowly to
avoid excessive spills.

The owner's and factory service manual likely specifies the use of
a non-hardening sealant on the engine block drain bolt. I use
Permatex Form-A-Gasket #2. I just apply it to the threads, let it
dry a bit, and put the bolt back in.

 

No way other than do it on your driveway and dilute with copious amounts of
water, or use a big drain pan. I usually manage to get most of it.

Another way is to stick the garden hose into the rad cap and run the water
until it comes clear. Oh wait, you need the block drain pulled to do this
right.

Yes, this works, except then you can't use genuine Honda coolant, which is
premixed. Also, you'd need to make sure you calculate for a 60%
concentration, as you've got no real idea how much is still in there since
you didn't pull the block drain.

If you think pulling the block drain on Honda motors is tough, you should
try it on a Mk1 Toyota MR2. It's ONLY accessible from UNDER the car, with
NO room for a cheater bar. I managed it anyway.

 

Yup. If the engine is running cold, it runs less efficiently.

I've seen this happen twice personally. Cars that failed the first test on
high HCs, then passed easily with nothing more than a new thermostat. Both
cars had exhibited poor heater output.

 

Re {flushing} vs. {draining and refilling} several times:

The Chilton's manual for 1984-1995 Civics gives a flushing procedure that is
different from a drain and refill. It says to
1. Remove the thermostat [which requires draining, which "requires" removing the
engine drain bolt]
2. Use a high pressure water hose and force fresh water into the thermostat
housing opening, allowing the water to back flush into the engine, heater and
radiator. Back flush until the water flowing from the radiator hose is clear.
3. After cleaning, reverse the removal procedures. Use new gaskets and O-rings
when re-assembling. Torque the thermostat mounting bolts to 7 ft-lbs. Refill the
cooling system with fresh coolant.

I guess we can disagree on what "no real idea" is. From my owner's manual:
1.35 gallons = total radiator coolant system capacity (see "specifications"
section)
1.08 gallons = radiator coolant system capacity less the reserve tank and engine
capacities (same section)
0.11 gallon = reserve tank capacity ("replacing coolant" section)

This yields a coolant capacity for the engine of (1.35 - 1.08 - 011 = ) 0.16
gallon = 2.56 cups = 0.64 quart.

The last time I drained my Civic's system without removing the block drain bolt
and not counting the reservoir, about one gallon came out. This led me to
believe the numbers above were good.

Note: The numbers above WILL vary depending on the year and model of Honda and
whether the car has an auto or manual transmission.

 

What car are is it?

You don't.... need to change it unless it fails. If you are doing a
coolant change anyway and the mileage is >100K miles it's not a bad idea to
change it.

You do not need to disconnect the lower radiator hose and even if you do it
will not drain more coolant than just using the radiator drain plug -
Haynes has generic info here which is not applicable to Hondas. This is
quite obvious when you look at the circulation arrangement and take into
account that the thermostat is closed. To drain the block, on any Honda
I've seen you need to remove the block drain plug... which is easy enough
to get out with a breaker bar - I just did it on a '99 Integra a few weeks
ago. If your plug is on the back side of the block, it may be a bit more
difficult.

Forget any flushing with water - it's not required and if you use the Honda
Type 2 pre-mixed 50/50 mix - which you certainly should - you will be
unable to get the correct concentration of antifreeze. If you can't get
the block drain plug out, just leave the old stuff in there.

If you're not doing a coolant change and want to change the thermostat,
just drain enough coolant from the radiator plug to prevent a spill when
you remove the thermostat.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??