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Discussion Starter #1
Someone hijacked my thread so I'll try again...


86 NA, 106 k miles. Bought it with a rusted-out exhaust, out of state. Trailered it, got the exhaust replaced, got it running. Showed a check engine light, used the BGB and found that the distributor was bad--replaced and timed in accordance with BGB.

Got it inspected, passed emissions, started driving it. Noted some "ping" when warmed up and under load. Dumped in some FI Cleaner and pressed on. One morning on the way to work, (at this point I have driven the car about 100 miles since I've owned it) it overheated on the freeway --I literally watched the temp gauge go from dead center of the arc straight to the top in about 10 seconds. Shut it down, coasted to a stop, popped the engine cover. I could hear coolant boiling so I let it sit for 20 min until the gauge showed normal. I was only about 1.5 muiles from work so gave it a try. Gauge stayed dead center.

After work, I opened the cap, filled it (took about 6 oz), ran for 20 min, no problems. Drove all the way home, no problems. Parked it, bought a new Toyota thermostat and some coolant, changed coolant and thermo and bled system IAW BGB.

Drove it about another week, and one day heard the boiling after I shut it off (temp gauge indicated normal). After it was cooled off, I re-bled IAW the two-page instructions posted on another thread here, including jacking the rear end up, etc.

Driving to work last Tuesday, once again watched the temp gage make its journey eastbound and shut it off. Let it cool, drove it home but this time had the temp gauge head east one more time. Each time I shut it down and let it cool, add water, etc. Got it home, jacked the rear, bled one more time.

Today, I got to thinking, maybe the timing is advanced, because it will sit and idle all day w/o overheating, but under load it is (sometimes) a different story. Retarded the timing (probably too much), let it sit and idle 30 min, no problem. Ran it about a mile up the road and back and coolant is puking out.

No coolant in the oil, no oil in the coolant. Pulled all spark plugs and none are steam-cleaned. All piston crowns show equal (not excessive) carbon build-up.

Checked catch-tank hoses for correct routing (not switched).

At idle I can run with the coolant cap off, no bubbles. I run with the rear jacked up, all the coolant bleed valves open, no bubbles there either, so I'm having a hard time imagining that it is a BHG...

No codes are set.

Update-
Removed radiator and checked through-flow with a garden hose, both directions unobstructed flow. Stuck the garden hose into each radiator hose. In one, the water came out of the coolant cap, strong flow. in the other, the water came out of the (open) engine bleeder valve located near the thermostat. Figured since I'm putting cold water into it the stat is closed so I couldn't get flow "through" the block.

Put it back together, bled yet again, and replaced coolant cap with a new Toyota part. Let it run a while with the flex hoses attached and the forward cocks open. Heater is receiving coolant flow as evidenced by the coolant in the flex line being quite warm. Radiator/radiator hoses are not warming to the touch, and the coolant in the radiator flex line is cool compared to the heater's.

As of yesterday, I bought a water pump. Took the old one off and it looks fine. No evidence of coolant leakage, the impeller spins smoothly, belt was snug. Judging from the sealant on it, the H2O pump has been changed in the past, and I suspect it was pumping just fine. Replacing it anyway, just 'cause I have it out, but don't think it'll make a bit of difference.

Looking at the cooling system schematic, I cannot quite see which lines I should be checking, but is it possible that there are completely separate coolant lines foir the heater core and radiator (not one loop). What are the chances that coolant is getting to the heater core but not to the radiator? Where can I stick my garden hose to verify this? (Especially with the water pump out, should be able to stick the hose onto the pump outlet side (external line)...where should the water come out of?

This is driving me crazy!
 

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Radiator loop and heater loop are totally separate. The heater loop is in the same "circuit" with the engine block. The flow through the radiator is controlled by the thermostat. If the hoses to the radiator are not getting hot, you either have a blockage in that circuit, or the thermosat is not opening (defective new one - or installed upside down).
 

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While the engine is warming up, feel the inlet and outlet hoses at the radiator to see whether heated coolant is passing through the system.

I think I already replied to you about my experiences in a previous post. I have had engines in two MR2 with blown head gaskets. Ironically the headgasket failures were in the same location. The failure in the head gasket occurred near the exhaust port of the #4 cylinder. Hot exhaust gases were blown into the coolant passage only when the engine had reached a higher temperature. I could drive all day long on the freeway if the temperaure was below about 77 degrees. If the temperature was above 77 degrees, the water temperature would start to increase after about 30 minurtes of driving:
http://www.pbase.com/aw11mr2/image/47264180
In the second engine I took apart, I also found pieces of sealant the previous owner had used to seal the water pump clogging some of the smaller coolant passages in the head gaskets. The semi-crescent shapes with corresponding two small holes in the head gasket are passages for coolant to flow between the block and cylinder head. In one of the engines I was working on, I found pieces of sealant clogging these holes.

If you have inspected, repaired, or replaced the rest of the cooling sstem, I suspect you have something clogged in the cylinder head, creating hot spot, a blown head gasket, or a cracked cylinder head.
 
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I must second Ron's reply because this is clearly not a routine problem, one that has a nagging nature, impervious to your previous efforts. You don't know how bad your little 2 was beaten before you bought it pig-in-a-poke. And, 4AGE's seem to warp heads and blow gaskets, sometimes spectacularly, sometimes just passing combustion gas into the cooling system. I say your car gotta bad head, bro.
 
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Sounds to me like the thermostat is failing,but hasn't failed yet.By the description I would guess that it is sticking 1/2 open,so the engine is staying cool at normal or slow driving,but not circulating well enough to stay cool at load.If its just sticking,it can come unstuck and work normal for a while,then the problem comes back. Eventually it will stick all the way open,or more often will stick closed.We run into this problem allot here in Canada during winter.Its cheap to replace,so maybe give that a try if you haven't replaced it yet.
 

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Discussion Starter #6 (Edited)
I'll see if I can

borrow a compression tester for those teeny little spark plus--mine was made way back when spark plugs took a 13/16" wrench :smile:

In the mean time, please help me to understand why I exhibit none of the following symptoms:

No oil in the coolant.
No coolant in the oil.
No steam-cleaned spark plugs or piston crowns.
No bubbles in the coolant, at idle or at higher throttle settings.
No loss of coolant (except when coolant in catch tank is boiling after engine is shut down).

Maybe I am in denial (sure don't want to change a head gasket) but it just does not add up, and I hate troubleshooting-by-parts-swapping (aka the lottery method).

The part that I keep coming back to is...why the apparent lack of coolant flow through the radiator? Note that it never seems to get hot, even though the heater does.

I really have to find a way to check flow through the engine, and understand the path the coolant takes...(see previous post above).
 

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Discussion Starter #7
follow up to Quag

just noticed your post.
Thermostat was replaced with a brandy-new Toyota part, step 1, paragraph three (installed in the correct direction). Thanks, but that should not be the problem...

Back to your regularly scheduled thread...
 

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I feel it could be the HG because it wouldn't take that much gas blowing into the cooling system to cause a gas pocket, and gas pockets really fight that coolant going up and down to get to and from the radiator. That's why I'd say it's just blown a little bit. You've done everything but stick the hose in the pump inlet and watch it come out the thermostat housing, without the thermostat in it.
But if you're absolutely positive that there is NO gas in the cooling system, I'd have to rule that theory out.
Here is a test I cooked up...... Remove the thermostat housing completley.
Water will flow around a water pump that is not turning, so you should be able to stick the hose in one side of where the thermostat housing was, and watch it come out the other. You said you checked the radiator to the cap, and it flowed strong. Check the other leg by sticking the hose into the line going to the water pump and watch it come out the thermostat housing.
Did you get crud out all these times of flushing?
 

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orionengnr said:
borrow a compression tester for those teeny little spark plus--mine was made way back when spark plugs took a 13/16" wrench :smile:

In the mean time, please help me to understand why I exhibit none of the following symptoms:

No oil in the coolant.
No coolant in the oil.
No steam-cleaned spark plugs or piston crowns.
No bubbles in the coolant, at idle or at higher throttle settings.
No loss of coolant (except when coolant in catch tank is boiling after engine is shut down).

Maybe I am in denial (sure dom't want to change a head gasket) but it just does not add up, and I hate troubleshooting-by-parts-swapping (aka the lottery method).

The part that I keep coming back to is...why the apparent lack of coolant flow through the radiator? Note that it never seems to get hot, even though the heater does.

I really have to find a way to check flow through the engine, and understand the path the coolant takes...(see previous post above).
I agree that it doesn't add up to a HG without those symptoms, but you might as well check and eliminate it as a cause. If you can borrow a compression tester, go for it. No harm, no foul. They're about $25 new with adapters anyhow now if you can't borrow one.

I see you got the water pump now. You still haven't said whether this is happening after replacing it. Presumably you haven't gotten it on there yet.

As far as water not reaching the radiator, there's a few reasons, and you haven't stated whether the lines are hot when there's boiling happening. I'm guessing you haven't checked when this has happened. You're probably checking with the car lidling for about 10-15 minutes at most. This isn't enough time to get water up there that's hot just idling. The ehater will get hot though becuase it is constantly circulating. Realize that with the valve open, it's acting like a second radiator making it nearly unnecessary in cool weather for the thermostat to open at idle. I know, I've tried the same thing when I was fighting similar issues. Yet if I drove, hot water would get up ther after a while. My lines weren't blocked, my thermostat was fine (or new), and everthing was flushing clean. It's shows a pretty healthy and over-engeinered system IMO.

Simply stated, I had that leak that wasn't leaking while I was stopped and looking. I got air in the system and it would overheat. I'd have a somewhat normal coolant level in the overflow, and it would boil lightly internally and boil out to the overflow if it was hotter. Temp guage would be normal and spike when the steam hit it. Then it'd go back to normal for a sec as water passed. I'd top off and be fine for a while until it leaked out again. Like I said, mine came out the water pump weep hole. I can take a pic... I think I have the old pump sitting in a box yet. There wasn't much residue, and I may have even smeared/scraped it off getting it out. The pump turns fine and it would seem like everything should be OK. It wasn't. The other place I later had a tiny leak was out the rear (driver's side) of the head where the coolant leaves to a heater hose. The seal that maked the casting to the heat had disintegrated and was allowing a very slow leak that left dried residue down the back side of the trans and toward the starter. You can look there as well. Also look at the area behind the water pump where the pipes lead for the head. There's a gasket and O-ring around there as well. It's possible that could leak as well.

Again, good luck. Keep poking around. You'll find the cause.
 

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Would be interested in how you're making out. I have a similiar situation. Runs perfectly up to a point, and then decides it wants to overheat - and fast!
 

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Discussion Starter #11
At this point I have a new water pump but am awaiting the o-rings. When they arrive I will install and try it but my level of confidence is not high. As a result I recently put a head gasket set on order...

I will follow up with progress reports.
 

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I know that you are centering on the cooling system being at fault, but have you simply tried retarding the timing? If it is too far advanced, it can heat the motor up really quickly, also check to make sure that your fans are coming on like they should. One other thing to check, which may or may not apply, when I drive my vw golf through rain, it'll over heat very quickly, as the belt gets wet, and stops turning the water pump
 

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I would set timing exactly as per BGB. I would triple check to make dang sure your cooling fans(2 of them) and the heat sensors are working correctly. I would also make dang sure ALL your radiator hoses are in fine condition. I had a bad radiator hose on one of my Mk1's, it had a internal bubble in the rubber of the hose, I only noticed it because I felt a weak spot on the external side of the hose. This was blocking the coolant and I was lucky in finding it.. Remember all these hoses are getting into the 20 year old range. BTW also on this particular Mk1 I had a semi clogged radiator that was not circulateing well at all. I thought it wasn't too bad until I put a new radiator in and ran the hose thru it....boy what a difference.(these radiators, if they are original, are 20 years old too and should be replaced....piece of mind....
 

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Discussion Starter #15
don't know who you are talking to--

me (original poster) or the guy who hijacked the thread with similar issues. I have already closed one thread and opened another because the same thing happened.

Please, if you are responding to me, READ THE THREAD FIRST. In the very first post I detailed how I have removed and checked the radiator, how I set the timing by the BGB etc. I know you are trying to help but the only piece of useful info was the defective rad hose. The rest only serves to clutter the thread, cause me to close it and start again.
 

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Orion
IMPO it sounds like flow problum. 99% of head or HG problums show at idol just as much as speed. You have no coolent loss, no steam, no milk in the engine, and no steam cleaned combustion chambers. With just that info I would not suspect head issues.
Have you removed the t-stat and ran the car without it? I know you have checked the rad with a hose but the water pump dosnt heve much pressure so it relies on volume of flow with low pressure and a half way restrickted rad can cause an over heating issue. You stated that the heater core hoses were getting hot but not the rad. Use a rag and vise grips and pinch off the heater hoses, If your coolent outlet hose at the motor has conciderably higher pressure or the return hoses get sucked shut you have a flow issue. Wile running the car this way use only water and leave the pressure cap off so you can see any chunkies curculating. The rad should get warm as it does you will be able to feal any cold spots-restrictions. If you find this to be true do your self a favor and dont try to flush it, just replace it, it is too late for a flush. I would look at every thing else before a head because if you do the head and have a simple flow issue you would have spent a lot of money and be in the same spot you are now. Hope this helps
Adam
 

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I had a heating prob. like yours once because the system would suck air in and cause the pump tp cavitate. When I would re-bleed it would run cool for a while and then heat up rapidly, usually on the freeway. It wouldn't leak water so I had a hard time finding the reason. I replaced all the hose clamps with screw type and tightened all the bolts-t-stat, water pump, etc. Problem fixed!!! Never has heated since. By the way, when it got hot, the radiator hoses weren't hot so I knew that there was no circulation. Let us know what you find.
Bob('85 since new)
 

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Discussion Starter #18
finally

got some decent weather and installed the water pump. Filled it up using the excellent bleeding procedure on this forum, and checked and adjusted the timing while it was warming up. Seemed to get hot at the cap but not at the radiator (again) so I shut it down.

Removed the oil cap and on the inside, FINALLY, some evidence of the blown head gasket--some guck on the inside of the cap.

All right, I have already ordered the head gasket set, so I'll have to get to work.

Never thought I'd be relieved to find a BHG, but after all the wondering and guessing it's a relief to have something solid to go on.
 
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