So a few weeks ago my '87 Duke overheated and left me stranded. The temp needle was pegged to the right and the engine compartment smelled like cooked motor oil giving me the impression that it was completely dead beyond simple recovery. I had it towed home and tried to start it the next day with no luck. Tried again the following day, same result.

This evening I decided I needed to get this back on the road because my truck is crap on snow and ice.

So I did a compression test on all 4 cylinders with a 120 avg on all 4. So I've ruled out a suspected blown head gasket. Also no water in the oil.

I then tested for spark on all 4 wires.... all good there.

I removed the valve cover and cranked it, valve train all functioning as it should.

I put everything back together and tried to start.... it fired right up and ran fine!! WTF?????

I let it run for a bit and it began to creep over the higher end of normal operating temp so I shut it down.

Before it died, the heater was not blowing warm air which made me wonder if the water pump had possibly failed. The pulley still turns fine and there is no bearing noise.

I can't understand why would it refuse to start for a couple days after getting it home, and now it starts and runs fine? I really thought it was toast!

I really want to get this back on the road, but I need to make sure it will be reliable. Is there any simple trick or method of determining if the water pump is actually circulating coolant as it should? It's not like most cars or trucks where I can just start it with the radiator cap off and see the coolant flowing across the opening.

Can I test the thermostat function with a propane torch?

Any other thoughts on what to check? I don't have a heated shop so practical effective shortcuts are much appreciated.... after a while I can't feel my hands out there :/

I would suggest the obvious things first... such as filling and "burping" the cooling system properly, and ensuring the coolant reservoir is filled to the correct level. You want to make sure no air is trapped in the system.

quote Originally posted by Patrick: * Make sure rad cap is the proper one for Fiero use. The catalogs are wrong! You want a non-vented one, * Check that the overflow tank and the small hose to the rad are both in good shape. Otherwise air gets sucked in. * Ensure that coolant level in overflow tank is at the "Cold" level. * Position rear end of Fiero higher than the front. * Remove thermostat housing cap and thermostat... and then add coolant to thermostat housing with rad cap also removed until coolant runs out the top of the radiator. * Re-install rad cap. * Continue to add coolant until you see the level come up to where the thermostat normally sits. * Put thermostat cap on and turn just barely enough to hold cap on. * Start engine and run for about 30 seconds. * Remove thermostat cap and check coolant level. * Repeat last four steps until coolant level no longer drops. * Re-install thermostat and thermostat housing cap. As long as there are no blockages anywhere in the cooling system and the water pump is circulating coolant, you should be good to go.

[This message has been edited by Patrick (edited 12-29-2014).]

I have the fill/burp procedure down and I have read (I believe in the oger's cave) about the correct rad cap...however I will double check the coolant overflow container hose. I had not considered possible ways for air to enter the cooling system. Are there any additional places this can typically occur?

I'm also concerned about what damage (if any) may have occurred as a result of the overheating and why it failed to start for 2 days after. It has always started right up prior to that. Now, a couple weeks later it fires right up? I'm happy it is running but also wary about furthering any damage from the overheating.

I guess I'm just more worried in this case because in the past if one of my other vehicles overheated, I just shut it down and after it cools down, add some coolant or whatnot and off I go. But in this particular case, I really thought it was dead, dead... It was smoking and smelled like cooked engine... I had to have it towed, I really thought I was facing a rebuild. This is why I am a little skeptical that I might not be totally out of the woods when it is now running seemingly fine.

There are a few more issues I would love to finally iron out with the way this car runs, but one thing at a time... the other issues are more or less annoyances that waste fuel. It is a manual trans, and sometimes when I push in the clutch and coast or stop, the RPMs will stay steady at 3k and if I am stopped long enough, they will gradually decrease until (after like a minute of no throttle) they are at a steady 900. This has randomly been happening for years. Sometimes it won't happen for a month or more. For the life of me I have not been able to determine what conditions trigger this to happen because it's always different. If it were consistent, I would suspect a vacuum leak. I have checked and or replaced all vacuum hoses anyway to be certain. And the other issue is that I suspect I am running rich, and this is only a guess based on the strong fuel smell of the exhaust. I recently (summer 2014) had a new muffler and cat installed and new timing gears, but these issues have been occurring long before that. My old cat was clogged.... I feel I should determine if my mixture is proper or risk shortening the life of my new cat.

I remember buying an ALDL to serial cable a few years ago for diagnosing the fiero ECM on a laptop... but I think I never used it because there was some reason it worked with every fiero EXCEPT my 87 4 cyl (it said that in the documentation)... or maybe it was my ECM that it was incompatible with... what a bummer. Things may have changed since then, it has been a while so probably worth revisiting.

[This message has been edited by perceptionist (edited 12-29-2014).]

It is very possible that your radiator is partially blocked especially if its the original radiator. Rust could have dislodged and blocked the heater core preventing it from getting water circulation now. You can test the thermostat by putting it in a pan of boiling water. Check under your passenger side carpet to make sure the heater core isn't leaking. As to why it started after sitting, you could have overheated the ICM or coil and after sitting for a long time it worked okay.

Reread entire coolant section of my cave.
Air can get in w/o leaking coolant out. Problem w/ Tstat cap or housing, WP Seal, etc...
Overheat might cause engine to shed rust then rust can block heater outlet. Block outlet will cause low/no heat and engine temperature problems.
Get a new Tstant. Stant SuperStant. Is cheap insurance.

If Intake manifold gasket is bad... can cause vac leaks, EGR problems, coolant problems including #4 cyl can "burn" coolant. (Can show #4 plug is different color then rest.) This is mainly cause by removing intake manifold then improperly installing after, like Gasket goes in dry but many adds RTV or install only w/ RTV.

Vac leaks, iffy power/grounds or iffy alt can cause idle issues.
Booster itself or line to it can leak.

Idle RPM could be need a updated PROM... See my Cave, 87-88 DIS Duke ECM

87+ DIS duke use P4 ECM type and won't work when software and/or hardware doesn't support 1227748 ECM.
http://www.reddevilriver.com/ does support DIS ECM

If fuel mix is major wrong the ECM will set DTC and turn on MIL light.
DTC 45 is good when MAT is toast and you idle in winter. MIL light turns off when you drive away but ECM saves the code.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

quote Originally posted by Csjag: It is very possible that your radiator is partially blocked especially if its the original radiator. Rust could have dislodged and blocked the heater core preventing it from getting water circulation now. You can test the thermostat by putting it in a pan of boiling water. Check under your passenger side carpet to make sure the heater core isn't leaking. As to why it started after sitting, you could have overheated the ICM or coil and after sitting for a long time it worked okay.

I forgot to mention that I put in a new radiator this summer as well. I mistakenly thought it was leaking but it turned out to be the hose which was also replaced. Now I have a spare rad

Thank you Ogre for the info! Could I easily rule out the possibility of leaking intake manifold gasket with starting fluid around gasket area and listen for idle change?

I am excited about looking into the ECM/PROM as the potential source of those other issues.

[This message has been edited by perceptionist (edited 12-29-2014).]

So I was lifting the rear of my car to fill when I heard leaking up front from the radiator cap which was securely on at the time. I lowered the rear and went to Autozone to grab a new GM 10409635 Non-Vented cap.

As soon as I looked at the new cap, it was obviously much cheaper quality than my existing one, but it was the correct one none the less. When I put it on, I could barely feel the force of the spring.... I have a brand new radiator so the neck was not worn or anything.

I lifted the rear back up and it started leaking at the radiator cap much worse than before. So I cleaned up my old cap and put it back on. The spring tension was nice and stiff as it should be. Then I lifted the rear again and no leak... even after filling at the thermo housing. I'm returning the new one tomorrow. I am concerned though because the rubber on my old cap is just beginning to crack, but I think I can get by until I find a better quality cap. Are there good solid quality caps still being made for these cars? Info?

As for the Thermo Cap, they did not have one, but said their store up the street did which was closed. I'm going to see if it is of decent quality tomorrow.

I'm pretty sure that my rad cap is allowing air into the system due to the small cracks in the rubber. That new cap was a total joke.

Oh another thing I noticed was different about the new cap.... The little disc in the center (which I imagine allows coolant back into the rad from the overflow tank) was not spring loaded like the one on my old cap was. Its a mild tension spring on my old one, but the new one had zero spring tension. Not sure if that makes a difference, but it was something I noticed.

quote Originally posted by perceptionist: Oh another thing I noticed was different about the new cap.... The little disc in the center (which I imagine allows coolant back into the rad from the overflow tank) was not spring loaded like the one on my old cap was. Its a mild tension spring on my old one, but the new one had zero spring tension. Not sure if that makes a difference, but it was something I noticed.

Ogre has a whole page dedicated to that at his site HERE.

Ah yes I had saved a copy of that some time ago in my collection of Fiero reference material. I actually referred to it before going out to buy my rad cap this evening. But after revisiting that page in the cave just now, I noticed a change that confuses me:

GM & AC Delco caps.

Sorry but I've dung into the Stant Ecat, 22P and finally check numbers below (11/2014) and found/confirm the problem...
22P list 10036879 and numbers listed here are Vented caps and wrong.

Thanks to "Two88GTs," the current GM and AC Delco cap numbers for Fiero are:

Rad Cap

AC Delco: RC27

GM : 10409635

Thermo Cap

AC Delco: RC40

GM: 6410941

"The p/n for the RC27 in my parts book is 10036879 which is still a valid number in the GM parts system but it is for the OLD design cap, and the remaining stock is indeed OLD. Get the 10409635."

Ok well it does not show up here with a copy/paste, but on the cave page the AC Delco and GM numbers under "Rad Cap" have a line through them... but then the last sentence says "Get the 10409635."

Unless I'm misunderstanding, first it crosses out the GM 10409635 number and then it tells me to GET the GM 10409635.

My saved copy from a while back is exactly the same only without the line going through those 2 numbers... so I went and got the GM 10409635 as referenced by that info. But yes after re reading the Cap info in the cave, it is certain that my new cap is the wrong (vented) cap based on the description of the vented caps.... but it was looked up as GM 10409635.

They may have had the wrong part under the right number... The box is "Duralast" UPC is "7 99304 97616 5"

[This message has been edited by perceptionist (edited 12-30-2014).]