4AC engine block steam holes

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rivera100
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4AC engine block steam holes

Post by rivera100 » Sun May 31, 2020 6:57 pm

Hello there,

New user here; first post. Hopefully this is right forum.

I am doing my first head gasket job on my 4AC engine and I'm confused about 3 particular holes in the block. I've uploaded 2 attachments which show the block with and without the head gasket overlaid on the block.

In the photo without the head gasket, there are 6 holes visible, labeled A through F. In the photo with the head gasket, holes A, B and C are covered while D, E and F are still visible. I believe holes A, B and C are covered by design but holes D, E and F, although still visible, seemed plugged up.

After further research, I learned they are "steam holes" and should be opened. I'd never heard of steam holes before but I guess they're used on blocks that have cylinders with shared walls because they alleviate steam pockets that can develop, e.g. small block Chevy's.

After cleaning crud out of them with a pick tool, I found that hole D allows passage to the other side of the block while holes E and F do not. In other words, if I shine a light or spray liquid into hole D, I can see it come out the other side by looking down into hole A. Holes E and F are still plugged and stop part way through, even after cleaning out as much crud as I could using a pick tool.

So my question is -- which is correct? On one hand, it could be that hole D is correct and E and F are so plugged from hardened corrosion that they need to be drilled out. On the other hand, it could be that hole D has rotted from corrosion and E and F are correct. For what it's worth, the cylinder head does have corresponding holes that line up with all 6 holes mentioned.

Can anyone advise on what I should do? Thank you in advance.
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NWMO
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Re: 4AC engine block steam holes

Post by NWMO » Mon Jun 01, 2020 12:24 pm

Welcome to the site Rivera,

There will be more knowledgeable folks than I follow, but as I recall, I cleared all three holes when putting my 4AC back together. I don't remember having to drill anything, but there was some grunting with a stiff wire as I recall.

Here is a link to Petros' head gasket replacement method, he has as much experience as any here. I did add the holes to the head gasket as he recommends.

Head Gasket Replacement Procedure

Chris

PS - There is a permanent link provided under "Repair Guides" and the tab "Repair Guides library of links"
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rivera100
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Re: 4AC engine block steam holes

Post by rivera100 » Mon Jun 01, 2020 9:28 pm

Hi Chris,

Thanks for the reply and the info on what you did with your 4AC. I'll give it another try using a stiff wire of some kind. The pick tool I was using has a tapered diameter so as it gets deeper in, it's probably getting stopped due to the limits of block's hole diameter.

Thanks for the link to Petros' head gasket replacement method. That post is legendary! I had accidentally come across it a few days ago and it inspired me to join the forum. Incredibly helpful and insightful.

-Rick

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NWMO
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Re: 4AC engine block steam holes

Post by NWMO » Tue Jun 02, 2020 9:39 am

I don't recall what I used, but working construction, I may have just grabbed a couple "flags" and used the wire off them.

Chris
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

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Re: 4AC engine block steam holes

Post by Petros » Tue Jun 02, 2020 5:59 pm

welcome to the forum!

the holes on the head are used to direct coolant to the parts of the cooling jacket in the head to attempt to maintain an even temperature, it is not a good idea to cut out the extra holes. the ones in the block are necessary during manufacturing, the head gasket is used to direct the flow as they are supposed to improve cooling performance.

As you can read in my thread on the head gasket, they made a mistake on the design of the 3ac head, it does not provide enough circulations around the (hot) exhaust valves, my solution is to open up some of these passages to improve cooling around the exhaust valves. I would advise against cutting out any more, it will mean coolant will circulate in an unplanned manner. possibly resulting in uneven cooling of the head, putting stress on the head gasket and head structure.

The coolant circulation around the exhaust valves on the 4ac appears to be revised, and is not as much an issue. But I do the same head gasket mod on my 4ac swap as I do with the 3ac. so you can likely stay with the factory head gasket configuration without the consequences as in the 3a engine. Or you can choose to use my head gasket mod as you see fit to improve head cooling.

Good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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Re: 4AC engine block steam holes

Post by rivera100 » Wed Jun 03, 2020 9:10 pm

Hey guys,

Thanks a lot for the replies and all the great information. It's really helpful.

Regarding something Chris wrote: "I don't remember having to drill anything, but there was some grunting with a stiff wire as I recall."

Do you mean to suggest that it was pretty tough to get the holes cleared out and you had to apply a lot of pressure and digging with the wire you used?

I also wondered, how did you confirm that they were cleared? Were you able to see that there was passage to the other side of the block through thhose holes?

Petros,

Good advice. It's mainly the proper circulation of coolant that I'm worried about, as you mention. As of now, only one of the holes in the block has passage to the other side but the two other holes do not. That inconsistency concerns me because I'm just not sure which is correct and how it might affect coolant circulation.

I haven't cut any extra holes in the head or the block though. The head would be left unmodified except for cleaning and resurfacing. The block is unmodified as well and would stay that way unless I can determine definitively that holes D, E and F (in the attached photo) should be cleared deep enough to allow flow to other side of the block.

I had considered your head gasket modification before I found this forum but was too worried to try it. Long story for another time, but the summary is that my car never used to go above 25% of the temp gauge. After an overheating incident, it now runs at 60% of the temp despite every part of the cooling system being replaced, correct timing, air bled out, etc. So I began to think it was something internal, e.g. cracked head or block, or now, possibly plugged-up steam holes?

Anyway, now that I know you and others have done your head gasket modification successfully, I may also do it that way to see if it alleviates the elevated engine temperatures.

Thanks,
-Rick

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Re: 4AC engine block steam holes

Post by NWMO » Thu Jun 04, 2020 6:33 am

Hey Rick,

As I recall, I may have tapped with a small hammer or similar item to get the wire through the plug and then knocked everything out. I believe the hole just opens to the area around the cylinder walls.

Chris
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

In remembrance of my friend ARCHINSTL:

T4WD augury?
"Oh, do not ask, 'What is it?' Let us go and make our visit."
T.S. Eliot - "The Love Song of J. Alfred Prufrock"

"Now and then we had a hope that, if we lived and were good, God would permit us to be pirates."
Mark Twain

rivera100
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Re: 4AC engine block steam holes

Post by rivera100 » Sun Jun 07, 2020 9:36 am

Thanks, Chris. I'll give that a try with a small hammer. If things don't budge after that, I'll probably just leave it as is, then see where things are at after reassembling, most likely using Petros' head gasket mod.

-Rick

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Re: 4AC engine block steam holes

Post by Petros » Wed Jun 10, 2020 11:16 pm

there is likely something else wrong. the temperature gauge reads the coolant outlet temperature. if one part of the head is not being cooled enough, it would not show up at the temperature gauge.

several items to consider: deposits in the radiator restricting coolant flow (vinegar soak and flush), lower hose closes down or collapses when the engine is reving about idle (the lower hose is too soft). the water pump sucks on the lower hose to bring coolant into the engine, if that lower hose is soft it will get sucked shut, and cause it to run hot. you may have a bad temp sender or gauge (that is rather rare, they are usually reliable, but they do occasionally fail). you have to get an after market temperature gauge to check the operating temperature, you can buy a cheap one at an auto parts store and rig it just to see the actual operating temp. poor connection to the sender, bad thermostat (just because it is new, or newish, does not mean it is good, take it out and test it). only by quality thermostats, made in Japan, or the USA. no communist made t-stats, many are junk right out of the box.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

rivera100
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Re: 4AC engine block steam holes

Post by rivera100 » Sat Jun 13, 2020 7:58 pm

Hi Petros,

Thanks for all those good suggestions. Beleive it or not, over the course of troubleshooting and replacing components, I did eventually hit all those points you suggested. A couple of comments...

All the hoses were replaced and checked for leaks. Those were all good. The radiator was also replaced and the whole system backflushed. Ran, drained, flushed several times with distilled water until it eventually drained fairly clear before putting coolant back in.

I checked the temp gauge in the dashboard cluster (even replaced the dashboard cluster to test and got the same results). I checked the temp sending unit connector by grounding it out and made sure it caused the temp gauge in the dashboard to spike to red. I checked the resistance of the temp sender unit itself with an ohmeter to ensure the resitance varied and correctly corresponded to the temperature being read.

I changed the thermostat each time I opened the system. They were always working correctly, opening fully at the right operating temperature when dropped in a pan of water and slowly heated. But since they're not very expensive, I always put a new one in.

I checked the actual temperature of the coolant by leaving the radiator cap off and sticking a thermometer into the radiator. That was normal. I also replaced the heater core. It did have a crack in one of the pipes. Water pump was totally fine but I replaced it anyway.

The only two tell-tale signs I came across were:

(1) while bleeding the system of air, after 20 minutes or so, it seemed to all be gone but then about every 5 minites (almost like clockwork), an air bubble would surface. Then nothing for another 5 minutes or so and another air bubble would appear. I bled the system for about an hour and the 5-minute air bubble would continue to appear. From my experience with other cars, it shouldn't have taken that long to bleed the air. Even raising the front-end of the car pretty high didn't help.

(2) I got a pressure tester, hooked it up to the radiator then pumped to 15psi. The system would not hold the pressure. It slowly leaked down about 1psi every 45 seconds or so.

So based on those two points, I concluded there must be air in the system that just won't bleed off. I couldn't find any evidence of external leaks (unless I just missed it somewhere in a hard-to-see area). So that led me to think it must be something internal, e.g. a cracked head or something. But the head has been tested and confirmed to have no cracks.

So in the course of cleaning and prepping the block, I noticed the 3 plugged up holes which I later found out were steam holes. But I had never heard of them before. And where two of the steam holes are still somewhat plugged but one is opened, I started to wonder if that might have had something to do with the engine running hot; hence this thread.

The head gasket needs replacing anyway so I'll see what happens after I've got it all back together. If the engine is still running hot and the air won't completely bleed or the system won't hold pressure, I might try adding dye to the coolant to see if anything external shows up.

-Rick

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Re: 4AC engine block steam holes

Post by Petros » Sat Jun 13, 2020 9:22 pm

sounds like an internal leak. cracked toyota heads or blocks are very rare, but I supposed it could happen. sometimes the engine plugs ('freeze plugs') can get rusty and leak round the edges, or an internal water pump leak (where the pump housing meets the front of the block).

make sure your head gasket face on the top of the block and the head are flat, that could be another problem. I have also seen the intake manifold have porisity, and leak coolant into the intake. there is a passage to warm the intake manfold from the head that passes coolant in it. That too is rare, but it can happen.

the cooling system is not that complicated, you just need to work your way down from obvious and common failure items, to less common and unlikely points of failure. as they say, first eliminate all of the possible places for it to leak, and than look for all the impossible places it might leak.

good luck.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

rivera100
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Re: 4AC engine block steam holes

Post by rivera100 » Thu Jun 18, 2020 8:40 pm

Hey Petros,

Thanks for the additional ideas. I hadn't thought to check the water pump for an internal leak. Externally, it seems fine and I can't see any leaks, even when pressure is applied. But internally, I know there's an o-ring that mates between the pump and the block. So maybe I'll pull the pump off and replace the o-ring for good measure.

After cleaning and prepping, the head and block faces are flat based on the measurements I took using a straight edge and feeler gauge in each of the directions specified in the service manual. So I think that should be OK.

New freeze plugs were put in when the previous mechanic rebuilt the engine. But I'll double-check those if I still have a hot-running engine after everything is put back together.

I've still got some more work to do like cleaning out the head bolt holes in the block and reattaching some components to the head. We'll see. Hopefully I can get everything working again soon.

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