Iron Duke - Cyl Head Swapped Out ... Questions... (Page 1/2)
82-T/A [At Work] SEP 27, 08:01 PM
Hey guys,

I'd mentioned before that my daughter was having issues with her Iron Duke. It ran AMAZING, but it had several issues:

1 - On a long drive, it would continue to blow out coolant seals. Coolant would either shoot out through one of the hoses, or blow a gasket by the water pump, or more recently... it literally blew out the radiator.
2 - On idle, it idles fine... when I blip the throttle after it's been sitting for a couple of minutes, I get a big puff of white smoke. The smoke smells acrid, and it's totally white. I assume it's antifreeze.


On a whim, I assumed maybe I had a cracked cyl head, so I bought a nice rebuildable one from Carter Carbs (thanks man!). I sent it off to the machine shop, and they did some work to it. I removed the 1985's cyl head, swapped out the valves and springs (since they are all brand new from the Fiero Store), lapped the valves, and re-installed them. I just installed new ARP cyl head bolts (with the one that has the Teflon in the correct spot), and torqued it down in sequence to 60-80-92 foot pounds. I haven't started it back up yet, I'm waiting for an intake manifold to come back from the machine shop... but I wanted to ask a few questions of you guys, to see what you think.


With the symptoms I mentioned above, let me show you some pictures, and tell you what I found when I removed the old cyl head...


On all of the valves, the little O-ring that I'd installed was not properly seated in the little slot, and it was deformed (see below):




Here's a picture of the engine block after I scraped the gasket material off:




The thing that concerns me, maybe... is that I didn't actually see anything at all that made it seem like there was a coolant leak (I also never got a milkshake mixture). But perhaps it could have been a crack between the valves? The cyl head itself (I can take pictures if anyone wants to see it) showed no signs of cracking or damage.


Here are some things I did notice:
- The pistons were very dirty and oily.
- The spark plugs were very clean (all four of them).
- The threads on spark plug (cyl number 4) had oil all around it.
- The intake valves were covered in oil, and the oil had caked on around the valve stem
- There was oil in the PCV valve tube... almost like it was sucking in oil?


One thing worth mentioning, the engine was basically a blue-print build, and my daughter did install a high-flow Melling Oil Pump that pumps 20% more oil. It's also worth mentioning that the engine only had ~110 miles on it since the rebuild.


I'm starting to think that the coolant problems have / had nothing to do with the cyl head at all. I'm starting to think maybe it's the radiator. Can anyone tell me why... if the coolant keeps exploding out of the engine from somewhere, that it wouldn't instead be pushing itself out of the radiator's overflow? It almost seems like it's not even using the radiator overflow. Am I potentially using the wrong radiator cap on the radiator itself, and it's perhaps, not allowing the coolant to escape when the pressure gets too high?

For the record, I fixed the "overheating" problem, which really wasn't a problem at all, but actually an issue with the coolant sensor. The sensor was new, but was a shitty one, and when I replaced it, it started reading properly.


Any help is appreciated. The newer cyl head is back on, and as soon as we get the intake manifold, we're going to install it.


Thank you!
Raydar SEP 27, 09:37 PM
Wow...
So, here's my story. I bought a rebuilt 3.4 from Grooms, through the Fiero Factory, and installed it myself.
With just a few hundred "break in" miles on it, it got to the point that it would idle just fine, for an indefinite amount of time.
But if I tried to drive it, it would force coolant out of the cooling system, and out through the overflow bottle.
It got to the point that I could cruise down the road with very few symptoms, but if I stomped the gas, it would blow a large percentage of the coolant out of the recovery tank.
It would soak the area between the radiator and frunk, and water down the road, where I had driven.
I want to say that there were also clouds of white steam coming from the exhaust, but I can't be sure about that, because coolant was just blowing everywhere. It could have just been blowing steam out of the cooling system.
I continuously checked the oil for evidence of coolant, but I never really found anything.
Long story short, I had a broken head bolt, that was allowing the head to "lift" off of the block, during high cylinder pressure. IOW, I had a blown head gasket.

The fact that you can't see a crack doesn't mean that there isn't one. I might suggest having a machine shop check the head carefully.
They have procedures (dye? magnaflux?) that can find cracks that are invisible to the human eye.
Duke heads are notorious for cracking, so I definitely wouldn't discount it.
Also, I don't know if Duke heads are known for warping, since they're cast iron. You might get it checked for that, too. But it's all kind of a "locking up the barn after the horse has escaped" kind of scenario.

Sorry... not a definitive answer, by any means. Just sharing my experience.

82-T/A [At Work] SEP 27, 10:42 PM

quote
Originally posted by Raydar:

Wow...
So, here's my story. I bought a rebuilt 3.4 from Grooms, through the Fiero Factory, and installed it myself.
With just a few hundred "break in" miles on it, it got to the point that it would idle just fine, for an indefinite amount of time.
But if I tried to drive it, it would force coolant out of the cooling system, and out through the overflow bottle.
It got to the point that I could cruise down the road with very few symptoms, but if I stomped the gas, it would blow a large percentage of the coolant out of the recovery tank.
It would soak the area between the radiator and frunk, and water down the road, where I had driven.
I want to say that there were also clouds of white steam coming from the exhaust, but I can't be sure about that, because coolant was just blowing everywhere. It could have just been blowing steam out of the cooling system.
I continuously checked the oil for evidence of coolant, but I never really found anything.
Long story short, I had a broken head bolt, that was allowing the head to "lift" off of the block, during high cylinder pressure. IOW, I had a blown head gasket.

The fact that you can't see a crack doesn't mean that there isn't one. I might suggest having a machine shop check the head carefully.
They have procedures (dye? magnaflux?) that can find cracks that are invisible to the human eye.
Duke heads are notorious for cracking, so I definitely wouldn't discount it.
Also, I don't know if Duke heads are known for warping, since they're cast iron. You might get it checked for that, too. But it's all kind of a "locking up the barn after the horse has escaped" kind of scenario.

Sorry... not a definitive answer, by any means. Just sharing my experience.




Ugh, thanks Raydar... that kind of sucks. Just curious, what did you end up doing? Did you end up replacing a cyl head?

The good news is... this replacement cyl head I got from Carter Carbs Afficionado, I went with a different machine shop (one that's closer, and more geared towards performance engines). They did magnaflux it when they serviced it, so I know this new cyl head is good and free of cracks. I also went ahead and bought a new radiator, with a matching radiator cap (that came with it)... a pretty decent one, so if it's either the radiator, radiator pressure cap, or a cracked cyl head... all of that will have been replaced, so we'll see. I'm just going to have to wait and see after I get it all back together.

I'm wondering about the oil though... why there's so much oil in the combustion chamber and the intake. That really doesn't make a whole lot of sense to me.


I'm thinking, based on your experience, and another post I found a couple of weeks ago... that I likely had a couple of issues. I wish I had taken more videos and testing of the Fiero when we got it, but it was barely driveable so I didn't think much of it. I can't remember if it was steaming then too...
Patrick SEP 28, 02:09 AM

quote
Originally posted by 82-T/A [At Work]:

There was oil in the PCV valve tube... almost like it was sucking in oil?




quote
Originally posted by 82-T/A [At Work]:

I'm wondering about the oil though... why there's so much oil in the combustion chamber and the intake. That really doesn't make a whole lot of sense to me.



Todd, this post may or may not be relevant to your oil issue. It worked amazingly well for my '84 duke. I put that mesh material inside of any/all valve cover baffles in both my duke and (for good measure) my Formula's 2.8 V6.

You probably need to further investigate what's going on with those O-rings on your valves though.
82-T/A [At Work] SEP 28, 08:07 AM

quote
Originally posted by Patrick:

Todd, this post may or may not be relevant to your oil issue. It worked amazingly well for my '84 duke. I put that mesh material inside of any/all valve cover baffles in both my duke and (for good measure) my Formula's 2.8 V6.

You probably need to further investigate what's going on with those O-rings on your valves though.




This is definitely helpful! I will absolutely do this, thank you!
Raydar SEP 28, 03:13 PM

quote
Originally posted by 82-T/A [At Work]:
...
Ugh, thanks Raydar... that kind of sucks. Just curious, what did you end up doing? Did you end up replacing a cyl head?




I told Ed what was going on. He told me to bring the car to him.
I dollied the car to the Fiero Factory. Ed's folks removed the engine, and sent it back to Grooms to be "re-rebuilt". Grooms then sent it back to Ed, and his folks reinstalled it.
He told me that Grooms reimbursed him for the R 'n' R. (I don't know that he ever told Grooms that it was a D.I.Y. install.)
I have often wondered about that. I think I even asked him point-blank, but I took Ed at his word.
But I was always sure to give him any business that I could, and to recommend him highly to everyone that I could.

I still miss those days. All the swap meets, Fiero friends, and etc.

Good luck with your daughter's car. I hope that everything is resolved.

[This message has been edited by Raydar (edited 09-28-2025).]

Dennis LaGrua SEP 28, 08:17 PM
IIRC, you built that engine and did not check the ring gaps before assembly. Could that have a bearing on the problem?

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

cartercarbaficionado SEP 29, 01:16 AM
sorry ive been a tad... absent as of late.
glad my cylinder head was good todd, hopefully thats all it was but I'd stud the block to try and eliminate a variable, i think the duke i took that head off of had a water leak around the timing cover area that went straight in the oil. if memory serves you had coolant spraying out the rad so id check the thermostat and the block. unfortunately i don't have a good spare for that currently
edit: actually used my good eye and read. i faced the same oiling issue on a "racing" 2.8l v6 and that was the exhaust forming excess backpressure and causing a absolute mess of oil in the intake manifold and cylinders and my buddies northstar 2002 sts did a very similar white smoke and its literally quarts of oil it burns at once and then it wont do it again which is weird.

[This message has been edited by cartercarbaficionado (edited 09-29-2025).]

82-T/A [At Work] SEP 29, 07:39 AM

quote
Originally posted by Dennis LaGrua:

IIRC, you built that engine and did not check the ring gaps before assembly. Could that have a bearing on the problem?





No, I don't think it's that. When she installed the rings, she made sure they were properly spaced. The rings themselves were correctly sized already for the very specific pistons we had, and the oversize of the pistons as well. We used the piston to ring chart for Hastings (which is where we got the rings for), so the gaps were already pre-set specifically for that piston and size.



quote
Originally posted by cartercarbaficionado:

sorry ive been a tad... absent as of late.
glad my cylinder head was good todd, hopefully thats all it was but I'd stud the block to try and eliminate a variable, i think the duke i took that head off of had a water leak around the timing cover area that went straight in the oil. if memory serves you had coolant spraying out the rad so id check the thermostat and the block. unfortunately i don't have a good spare for that currently
edit: actually used my good eye and read. i faced the same oiling issue on a "racing" 2.8l v6 and that was the exhaust forming excess backpressure and causing a absolute mess of oil in the intake manifold and cylinders and my buddies northstar 2002 sts did a very similar white smoke and its literally quarts of oil it burns at once and then it wont do it again which is weird.




It seems like there's just too much pressure in the cooling system at certain points. But it doesn't overheat... but yeah, it would blow hoses and such. This is with or without the thermostat. About the only thing we didn't change out was the EGR valve. So, I'll see... but I'm going to try Patrick's trick and see what happens.

I'm convinced there are two problems.:

- Coolant blowing out of different places when it's running hot. I'm convinced this is because of a bad radiator cap that's not properly relieving pressure. I don't think I've ever seen the overflow actually do anything. This could also possibly have been a head gasket issue... not sure.
- Too much oil in the combustion chamber. I think this could be as a result of a bad PCV (or maybe installed backwards) and those little O-rings. Not sure, but I've put everything back together properly, so we'll see. Maybe I just used bad valve stem seals.
Frenchrafe SEP 29, 08:01 AM
I think yhat you have two issues:

1. Oil getting past the inlet valves guides and/or excessive crank case pressure (blow by from the rings).
2. A coolant pressure anomally.

For the first, maybe the new head valves guides will be in better spec? Shame the iron dukes can't use more recent style valve stem seals. If not, then it's another rebuild with new rings and double checking the ring gaps!
For the second, check the radiator cap. Is it actually opening at specified pressure? (Letting the excess into the overflow when hot.)
As I've said before on this forum, I had a rather severe coolant leak into the exaust tracts on my engine. Since it was not going into the cylinders, I just did the coolant flush / rinse / Holts block weld / empty / refill with fresh coolant.
Ever since, no more problems.

------------------
"Turbo Slug" - '87 Fiero GT. 3800 turbo. - The fastest Fiero in France! @turboslugfiero
https://youtu.be/hUzOAeyWLfM