1987 Isuzu Overheating

- Air bubble in the system? Have you drained the block or radiator and refilled with coolant? If so did you make sure you followed the directions to get all the air out?

- You can have a leaking head gasket or crack in the engine and never find coolant in the oil. It happens sometimes. Combusted gases have a higher pressure than the coolant system, and flow into it. When you shut it down, the coolant does not always backflow into the cracks. (Usually maybe, but not always)

take the radiator cap off and see if the coolant continues to rise. rev the motor and see if it gets worse with the cap off.

I have done this before, but not allowing everything to come fully up to temperature. I did it for a while with the thermostat removed as well as installed also.

I saw coolant flowing across the top of the radiator, and it seemed that as I increased RPM, the level would drop slightly. On return to idle, it would rise and overflow a bit. Is this a problem or normal behavior?

So it happened again this morning, after all tests last night were inconclusive. I lost much of the coolant within 5 minutes of starting out this morning, stopped, refilled once cool enough and then drove 40 miles to work. The system did not lose any more coolant during the trip after the refill.

I have a hare-brained theory: Suppose there is a bad / loose seal somewhere that only leaks when it is cold. The initial start and warmup brings pressure up in the system and allows coolant to leak only when under pressure and the seal has not yet warmed enough. Then after everything is above temperature X, it will not leak anymore, or at least not enough to leave any drips when I'm looking for it.

Surely, there's gotta be a simpler answer, but I sure don't know what it is right now.

I would yank the tstat and run it for a couple of days... You may have got a bad one. Did the tstat you put in have a jiggle valve? If not I'd drill a 1/8th hole somewhere on the tsat to help it bleed air. HTH, Ben

Aluminum heads seal better when hot. The aluminum expands more than the steel bolts that clamp it down. When you overheat the head it expands too much and crushes the head gasket. A lot of head gaskets on cars with aluminum heads leak much more cold than hot.

I ran for a day with no thermostat and the system did not overheat. I also installed a second new thermostat and the problem returned the next day. Both of those t-stats have a tickle valve.

Can anyone offer up advice on a good technique for bleeding the cooling system on that 1987 Isuzu 2.3L engine? Maybe I'm just not getting the system full?

Mitchell doesnt specify anything spooky besides making sure the heater is on max hot before refilling. How long are you running the engine with the radiator cap off while refilling? Sometimes it takes a while... HTH Ben

Rev up the engine good to really get good water flow to force the air out. I usually do it when it's just gotten warmed up with the radiator cap off and before I've completely topped off the radiator.

More on this problem:

In the act of shotgunning, I decided that a new water pump wouldn't hurt. In the process of removing the ware pump, I discovered that the timing belt cover needs to be removed, both the top and bottom halves.

I now have a very stuck damper/lower pully center bolt, which has resisted all my efforts this afternoon to come loose and I'm left wondering:

Do any of you know if this is a reverse thread on this pully bolt? The Haynes manual makes no mention of it, but I'd hate to think that I spent the day over torquing the blasted thing. I did try the reverse direction a bit, but not nearly as hard as the 'proper' way.

Thanks!

Did you try the ole' hang the breaker bar near the frame and crank the motor trick? HTH Ben

Yessir, Either it is a reverse thread, or my starter doesn't have enough torque to break it free. I even made enough room to get my impact wrench in there and cranked to pressure up to max. No dice.