Overheating Mystrey - 95 Honda

[john]

You guys always come through for me, and once again I am not having any luck getting good info from any Honda sites.

'95 Honda Odyssey; 4cyl, 2.2 liters; 200,000 mi.
-last fall the heater core failed in a cloud of steam and water; I bypassed the heater core. The car ran well after this until:
-3 weeks ago car began to overheat... steam was venting near thermostat... I replaced the thermostat and gasket.
-2 weeks ago a small hose leading to a control valve sprung a leak. I replaced the hose.
-1 week ago the radiator (only 1 year old) blew a seam. Replaced the radiator, and also removed the brand new thermostat. Drove the car less than a mile and the heater core bypass host blew off... It had been joined with hose clamps and a plastic insert... the insert cracked in half.
-the electric cooling fans operate normally.
-the only original part left was the water pump so I replaced it (a 2 day job; really makes me appreciate my Tercel)
- after replacing the water pump, I let the car idle for about 6 minutes. Temp gauge read normal (slightly below 1/2). I went for a drive, within 200 yards the temp started to rise above 1/2. I stopped the car and checked that my electric fans were operating...they were on. As I closed the hood the heater core bypass hose blew apart again. The gauge temp was probably at 3/4 hot at that point.

Any ideas? I seem to have a cirulation problem. When I removed the old original water pump I was disapointed to see that it seemed perfect; I had hoped to find a broken impeller.

I noticed that as the car's temp would start to rise, the radiator hoses would feel medium hot... however the heater core bypass hose I installed would be red hot.

Before I installed the new pump I took my garden hose an fed water into both radiator hoses... the water exited where the water pump would be. I did the same with the heater core bypass hose... I fed water from my garden hose into the bypass hose, both directions, and the water exited where the water pump would be. I seem to have great flow through the engine. I would like to keep this car for about 1 more year and then dump it.

As always, I will appreciate any help my Tercel brothers can give me. - john

[rer233]

hate to say it John, but sounds like a head gasket to me. not real familiar with your particular honda model- is there a bleeder for the cooling system- maybe near the t-stat? if the system's properly bled and full of coolant, don't see how it can be anything else. seems like the system's generating too much pressure- i assume you've changed the radiator cap?? good luck.

[john]

Thank you for the reply. I replaced the head gasket last June. The car had been losing coolant before that and I could not pass smog.... it had poor compression in a couple cylinders. I took the head to a machine shop, and a couple burned valves were replaced, the head surfaced and lots of rubber o rings replaced. The car ran very nice after that, good compression, and I passed smog.

There is a bleeder next to the thermostat housing. I got a good stream out of it before closing it. Topped off the coolant.

The head gasket is the only thing I can think of also. I guess I will give it a compression check and see what I've got.

I will put the thermostat back in also and change radiator cap.. current cap is only several months old, and radiator is brand new...yay for lifetime warrenty at autozone!

[Petros]

are losing coolant? If so than I would also suspect head gasket. I have rebuilt several honda motors, but I am not familar with your model, but I do know the honda has a very sensitive head gasket in terms of installation. Sounds like, either all of a sudden all your hoses need to be replaced all at once, or the system is being over-pressured. check the cap, and do your compression test and see if your head gasket is questionable, If you need to do it again I suggest you use the same procedure I have over in the repair guilds section for replacing a Tercel head gasket.

You should plane off the top of the block with wet and dry paper and a large stone or steel sanding block (this can be done with the engine in the car, just clean up real good when done). Honda blocks are usually pretty durable but they should be decked before a new head gasket in installed. I would also give the head the same treatment because machine shops typically leave too rough a surface on the gasket face and it is not always perfectly flat (their machines get worn, the bearings give a bit of wobble to the cutting head). So give the head face a hand sanding as well per my procedure. clean both surfaces very good and of course use a new head gasket installed clean and dry (no sealant!).

I presume you had the head checked for cracks? Honda, like Toyota, usually makes pretty good parts that are not prone to cracking, but if it was overheated badly it could be damaged beyond repair. Not likely, but worth doing a crack check once the head if off.

Also, it at about the age where all the rubber parts should be replaced, honda designs their cars to run about 200k miles real reliable, after than minor things like seals and hoses can just start failing one after another.

If the radiator is good, the water is circulating, t-stat is good, no air in the system, it should not over heat. So either one of these elements of the cooling system is bad (which it does not sound like it), or the head gasket or head itself is damaged. So make sure both the top of the block and the head face is flat and smooth, clean the head bolts (or nuts, some hondas use studs with nuts on the head), and following the torque procedure to the letter.

good luck. this kind of problem is very frustrating, but once you find the problem and fix it your Honda will be good for another 100k miles without any overheating problems at all.

[john]

Thank you for the help Petros.

-Tested the new thermostat (made thermostat soup and it opened fine. Put it back in car, properly oriented.

-repaired heater bypass hose, used metal hose connector from hardware store instead of plastic hose connector from auto parts store.

-opened bleed valve on thermostat housing.

- warmed up car and got good water flow out of bleed valve.

- car was at normal operating temp and steam began escaping at the heater core bypass connection.

-shut car off and checked compression: #1 cyl is 170lbs; #2 is 170; #3 is 179; #4 is172

- I now believe that head gasket is fine. Last June The machinist checked the head for cracks and replaced all the many rubber o rings and stuff.

So
-Top radiator hose gets hot.
-lower hose is a little cooler than top.
-heater core bypass hose is still red hot , leaking steam , and ready to try and burst at normal operating temp.
-both fans come on.
-radiator is brand new.
-radiator cap is only a few months old and has a nice seal. I seem to remember being offered a standard cap or one with a pressure release valve. The car has always had a standard cap. Is the pressure release cap offered to try and keep nitwits from scalding themselves? Or does the pressure release cap actually keep the system from overheating? The current cap looks like the one it has always had, no lever on it.
-replaced water pump yesterday.
-seems to be excellent flow of water through all hoses.

I am completely out of ideas.

[Petros]

check your temp gauge, get one from an auto parts store, the accessory type (they do not cost much) and than put it in and drive around watch it. See if the temp fluctuations act the same. So you might just need a new sender. if they go bad they can fluctuate the gauge up and down.

BTW, many of the Chinese made thermostats act poor right out of the box, many are questionable even when new. The temp will fluctuate up and down with a poor one, even though it opens in a hot water test. Buy only the quality ones that cost about $15 to 20, not the $6 ones (they are junk).

BTW, a marginal head gasket may still show a good compression test but still leak water. If you can stop the obvious leaks and just drive it for a few days to you still loose coolant?

[keith]

When you replaced the head gasket, did you oil the threads on the bolts? The torque specs call for oil.

[john]

Good news! The honda is back on the road. A new head gasket cured the problem. I did not realize that I could have good compression and a bad gasket. Once i cured all the external leaks, I could tell that the engine was drinking lots of water. Thank you to all my Tercel brothers. My 85 wagon was my main vehicle for two weeks... I really do enjoy driving her. She still needs some front end tweeking and 4 new tires, but man she starts and runs so smooth. I love the look of other drivers when they see an old man in a station wagon leave them at the light.

[Petros]

good to hear, Yes, the compression when you crank the engine is about 200 psi, but during normal operation the peak pressures in the combustion chamber can be as high as 2000 psi (that is why the head gasket installation is so sensitive). this can lift or distort the gasket and not only over pressure the system, but also allow coolant into the combustion process on the intake stroke.

On older cars with massive cast iron heads and blocks I imagine they were not nearly as sensitive, but not with modern aluminum lightweight engines. With a honda, they are very durable and reliable, but once you over heat it just once, the gasket breaks its seal and it almost always has to be replaced again. A badly overheated honda can mean junking the head, I have seen them melt and warp badly. Part of the cost of a very light and precision engine.