I noticed that my mother-in-law’s Accord is leaking coolant from the interface between the engine block and the thermostat plastic shroud. See the two attached pictures.

Is this common? Is this due to the thermostat or thermostat housing being broken? I plan to dissemble, clean, and reassemble this area this weekend making sure to tighten the bolts to whatever torque is specified in the manual. Should I expect to replace any other parts such as any seals or gaskets? Please ignore the leaky valve cover gasket in the pictures which needs attention as well.

 

That is actually referred to as the water outlet. With the car running are you able to see exactly where the coolant is leaking from? If it's only coming from under/around the water outlet it is probably a worn/broken O-ring/gasket. if it is coming from a small crack in the the outlet, it will need to be replaced. Honda Part No. 19360-PAA-A00.

If there are no cracks and you are looking to clean it up and stop the seal from leaking. You will need to replace the rubber o-ring gasket that is between the water outlet and the head. Honda part No. 19313-PT0-000.

 

While the car is running I can't tell where specially in this area the leak is coming from. Most of the edges are covered in what looks like dried coolant. I added a close-up picture below. The coolant overflow reservoir is empty; maybe the coolant is too low now to leak from this point?
Thank you for suggesting these two parts; are both of them typically inexpensive and readily available? Maybe it’s best to replace both when the components are disassembled.

 

$2-$5 for the gasket and $12-$20 for the outlet at a Honda dealership. Not sure if they are items that a generic auto parts store would carry. Usually if you clean both surfaces up and replace the gasket that is all that would be required.

Make sure that the coolant in the rad is not low. You should try never operate the engine with a low coolant level. It could overheat and cause permanent damage to the engine.

 

OT:

I'm having the same problem with my 91 accord accord. Im pretty sure my leak is coming from the water outlet(idk if thats what you guys call it, the housing that holds the thermostat that connects the water to the block)

I found out that my O-ring is worn out. I need to know whats the part number for that O-ring gasket for a 91 accord and the part number for the water outlet that holds the thermostat as well.

I tried using silicone but it wont work. Should I buy it online or a local oreilly pepboys autozone etc should carry it?

Anyways, Can someone help me with the part number for 91 accord ex o-ring gasket part number. Thanks

 

The Upper rad hose water outlet O-Ring is Honda part number 19313-PT0-000

The thermostat housing has two parts,

Thermostat Case - 19320-PT2-000 (main body that holds the T-stat)
Thermostat Cover - 19311-PT0-000

 

Do you think a silicone will do the job?

 

@jonathan12
NO you need the o-ring. Do it right the first time it saves on the headaches.
Note:: check the inlet bypass hose as you are there. It is also cheap and being a 91 if never replaced it may be a good time to do so.

 

You can use silicone but you need to do it right. It's really not worth the hassle but if you want this is what you should do.

Clean it real good. Make sure there is no coolant at all either in the head or the outlet housing. Then put a small amount of the rtv blue on the housing around the ring area. Then set it gently against the head without squeezing it against it. You don't want it the squeeze out Then gently put the bolts on and finger tighten while holding the housing gently against the head. You don't want to completely tighten it, just make sure the bolts hold the outlet housing on the head. Then let it sit for a couple hours to let it cure. Then you can tighten it down and let it sit again for at;east a couple more hours before trying to add coolant. I would just let it sit overnight myself.

As you can see it's probably better to just buy the gasket. lol

 

I already tried using the black silicone. But it didn't work. Do I have to take out the silicone left overs before I put the O-ring?

Whats an inlet bypass hose look like? How does it look like? and do I have to replace it with the OEM hose as well or I can use the hose that a local auto shop sells?

Because I spent $15 just for that O-ring gasket.. Gasket was $3 handling fee was $5 and shipping was $8 for a really light weight part...

 

Yes the more of the silicon you get out the better.
The inlet bypass house is the small house that loops from the front just after the thermostat to just before the housing meets the block. Just check it for dry rot or cracks, if none then you should be alright. It is a special house because it loops you would have a hard time fitting a straight piece of hose there. It can be done if you know how to do it but at the same time it would just be easier to get the right hose.
https://honda-tech.com/forums/honda-accord-1990-2002-2/coolant-bypass-nipple-barb-3000651/
Go down to the 7th post and look at the second photo down. that is where the inlet bypass house goes from and then goes to.

 

*hose not house LMAO now if you excuse me I need to head back to spelling class

 

So basically I need to change the U-shaped hose? Which is the coolant bypass hose? You think a local auto shop sells those?