I need some help. I have been chasing a leak at the thermostat cap for 4 months. (I changed out the thermostat over the winter and have had issue ever since. I also had the heater core changed out .) I am on my third or fourth thermostat, my second cap, I burped and burped it I filled it and filled it and burped more. I have tried to remove corrosion on the neck both at The cap and where the thermostat sits. We have a new/old thermostat housing or neck so I guess that is next. 134,000 miles 1987 Fiero GT, V6 Auto. I am a girl so keep it in English please!
Thanks!!!
JJ
------------------ JJFieroFan 85 2m6 (85-91) 85 2m6 CLONE (00-14) sold to a friend 87 Fiero GT (13-now) 07 Nissan Murano SL AWD ((07-now) Back in Black
The top of the thermostat housing can get bent from improper removal of the cap (ie using a big honkin' pipe wrench to remove it), so you need to make sure it's flat. I've used sandpaper on a flat surface (when the housing was off the engine) to see where the high points were, but something similar can probably be done while the housing is still on the engine. You want the top edge of the housing to eventually be corrosion free and flat, otherwise even a new cap won't be able to seal. And when the cap is put on, push down while turning to make sure it's turned all the way (past the first click and to the end).
[This message has been edited by Patrick (edited 07-12-2015).]
When you install a thermostat, is it not "snapping" into place? If not, you need to get rid of any corrosion that has built up where the thermostat rubber seal is supposed to sit. And I hope you also apply a good coating of grease on the rubber seal before you install the thermostat. Makes it much easier to snap into place.
I had the same issue with 2 Fiero store caps over a period of time. I since switched to a Delco cap and felt a difference getting the thing on, much tighter fit. Since then I've never had another issue with cap leakage.
I put the thermostat in, locked it into place. I thiought so anyway. It was up by the cap and coolant was leaking freely. I will try again. On my third cap, but I can get another. I did use Vaseline when I installed it.
[This message has been edited by JJFieroFan (edited 07-12-2015).]
Like Patrick said, use sandpaper on a flat block and sand the top of the thermostat housing, you will see a silver ring start to appear on top through the corrosion, keep sanding until you get a full ring around the top, a nice smooth sealing surface. That will usually fix it.
I had the same issue with 2 Fiero store caps over a period of time. I since switched to a Delco cap and felt a difference getting the thing on, much tighter fit. Since then I've never had another issue with cap leakage.
That reminds me of a discussion we've had here previously... I forget if it's a brand thing or a generational thing, but some of the thermostat caps have a seal that does not spin independently of the cap. Those caps are awful as it's very difficult to open or close these caps when the rubber seal is forced to rotate/rub on the top of the thermostat housing. On the good caps, where the rubber seal spins independently of the cap... the seal can stay put on the housing as the cap is turned and tightened (or loosened).
[This message has been edited by Patrick (edited 09-12-2019).]
Cap appears to be ok. There is corrosion on the top which I got taken care of. Think and corrosion at the thermostat seat that I am still working on. Any suggestions as to what to use to get down there and clean it up??
I put the thermostat in, locked it into place. I thiought so anyway. It was up by the cap and coolant was leaking freely. I will try again. On my third cap, but I can get another. I did use Vaseline when I installed it.
The thermostat cannot be "up by the cap" unless the handle is missing or bent. Which thermostat are you running?
EDIT: should look like this:
[This message has been edited by Hudini (edited 07-16-2015).]
Stant 195. It is Not bent. There is so much corrosion on the inside of the neck that the cap does not seat. It floats back up when you rev the car. I am going to work on it this weekend. I had a lot going on this week and have not gotten to it. It had a bent one at one point and I do know what that looks like. If you feel where the thermostat should sit it is very rough. I have not been able to get it smooth. I had some corrosion at the top also. Believe me it does sort of float up . The top of the handle pushes against the cap. At best it drips at worst it leaks like a sieve. Thanks for the imput.
JJ
[This message has been edited by JJFieroFan (edited 07-16-2015).]
A common mistake is to tighten the thermostat fill cap while the thermostat is not fully seated. You put the cap on, twist it to close and the cap bends ever so slightly causing a leak. I apply a small film of silicone grease on the water outlet sealing surface. to make the cap easier to tighten and seal, but always make sure that the stat is full seated before putting the cap on.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Heddman Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, 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 "
To determine if it's the thermostat causing the problem or the cap, leave the thermostat out and check for leaks. With the thermostat out, the cap has nothing pushing it away from it's seal, so if it still leaks, it's the cap.
Very likely you are worrying to much. Is a lot of BS to "burp the system," worse when you have a Fiero.
1. "Burping" will not remove all air from system. Fill system using short directions in my Cave, Coolant Fill Air left will move to radiator then rad cap and overflow tank removes that after you run engine a few heat cycles. every time you start cold to warm air is pushed out. after shutdown coolant from tank will be suck back. This can take days to work air out of the system.
2. Before 1 can work OR rad cap or overflow problems then the tstat cap will always have air as soon as you loosen the tstat cap. That make people think is Tstat bad but is not true. Just the wrong Rad cap can fake Tstat cap problems. See my Cave, Radiator Caps
3. Tstat housings can rust causing seal problems. This mostly causes coolant leaks out of system. If not bad can try just a wire brush then thin coat of silicon grease to stop rust. Seal area w/ pits then clean and solder coat (called Tinning) to stop future rust. Solder can fill/sooth the pits so cap can work. Cap Rubber won't care if housing is not completely OE spec. If the housing "ears" to tighten the cap are bad... get another housing.
------------------ 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)
Thanks for all the info. I have read Ogres cave section a few times!!! 😄 I have recently met an experienced Fiero mechanic who is about 20 minutes away. I am going to get him to look at it. Hopefully I can drive it there. I have spare housing and cap... let him sort it out. Thermostat is out. Hoping no leak or less leaking. I won't run it without a thermostat except to get it to the shop. Thanks everyone I will reply when we figure it out!!! Thanks all!!! JJ
Thermostat out. So far no leaks. I have run it twice and revved it a bit yesterday with no leaks. Looks like I will replace the thermostat housing with a good used one. JJ
Yes, I will test it again to be sure, but I let it run for awhile and revved if or higher rpms. Still plan to change out housing, cap, hoses, and thermostat anyway. Just want to get it to a good mechanic and let them fix it. Thanks!!!
Patrick you were right about the cap. I fit a new one today as I was still leaking when I revved it hard. I had cleaned and sanded the rim and got a great fit. I plan on taking it in and getting it checked out and new hoses put on ...etc. Thanks!!!!
