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| 3800 - No Heat When Thermostat Installed (Page 1/2) |
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Matthew_Fiero
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AUG 10, 10:16 PM
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Hi Everyone! I hope everyone is doing well and safe.
I've been troubleshooting an issue I've been having with no heat getting to the heater core when the thermostat is installed. When the thermostat is off I definitively feel heat.
Specs:
85GT
1998 3800 Series II
Coolant is routed as follows:
Coolant enters at the timing cover port and exits at the modified Fiero thermostat. One of the heater core hose connects just under the snout (under the vacuum port) and the other at the modified thermostat housing.
I have been using Bluedriver Live when driving and see the engine coolant reaching up to 98-99 C (210 F) and operating around 94 to 99 C or 200 to 210 F.
The thermostat installed is a new Delco 195 F. I have tried 2 in total with another replaced last night.
The radiator is an aluminium Champion radiator (thanks Archie) with a new 16PSI Stant 10330. By the way these caps are super sensitive and can seat crooked. Coolant no longer flows into the recovery tank when performing the fill procedure.
I have removed the top hose at the heater core and while filling it coolant started coming out of the core where the hose was removed from so it doesn't appear to be blocked.
The engine operates smooth and I see no evidence of air bubbles. The stock temperature gauge doesn't read correctly but does jump around sometimes ever so slightly. The needle starts at the beginning of the scale and never reaches the middle. Hence why I'm using Bluedriver to monitor the ECT.
I'm stumped on where to go from here short of replacing the heater core which seems to operate without the thermostat installed.
If the thermostat wasn't functioning properly the engine temperature wouldn't be so steady. I've yet to see the engine go above 101 C (214 F) and therefore no overheating issues ever.
Thanks for reading and if you happen to have any insight I would appreciate hearing any thoughts.
Take care and stay safe,
Matthew
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fierofool
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AUG 10, 10:34 PM
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The stock 85GT had a nose that came off a nipple on the water pump. On the trunk side of the water pump. It went to a rubber hose that looped around to a metal tube mounted on top of the frame rail. That was the feed for the heater core. Are you utilizing that path to feed your heater?
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Matthew_Fiero
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AUG 10, 11:07 PM
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| quote | Originally posted by fierofool:
The stock 85GT had a nose that came off a nipple on the water pump. On the trunk side of the water pump. It went to a rubber hose that looped around to a metal tube mounted on top of the frame rail. That was the feed for the heater core. Are you utilizing that path to feed your heater? |
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One end is connected on the LIM under the snout and the other off the modified Fiero thermostat housing. The hoses both go directly to the underbody tubes.
I hope this answers your question.
Matthew
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fierosound
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AUG 10, 11:17 PM
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On the V6 engine, the hose connection on thermostat housing BELOW thermostat is supply line TO heater core.
This way, the heater core gets coolant flow when engine is running regardless of whether thermostat is open or not.
On 85-86 cars RETURN line connected to pipe on Water Pump, pulling coolant through system when engine is running.
The 87/88 cars had this line connected to a Tee on the coolant return pipe under the car.
------------------
My World of Wheels Winners (Click on links below)
3.4L Supercharged 87 GT and Super Duty 4 Indy #163[This message has been edited by fierosound (edited 08-11-2021).]
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fierofool
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AUG 11, 06:54 AM
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Matthew_Fiero
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AUG 11, 08:27 AM
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Thanks for sharing this. I can't tell you how many times I've read this post. Unfortunately I'm not using the alternator bracket that came with the engine so my setup is different.
Matthew
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Matthew_Fiero
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AUG 11, 09:13 AM
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Going by the pictures in that post I have B capped off at the timing cover and instead connected to the connection on the modified Fiero thermostat.
Matthew
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Matthew_Fiero
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AUG 11, 06:53 PM
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Wait... Have I been the Fiero fool the whole time?
Do I have the wrong port blocked off?? The red circle at the timing cover is currently capped and the yellow circle is where I am utilizing the elbow with a coolant hose clamped to it.
Are you utilizing that path to feed your heater?
I would say no.
Matthew[This message has been edited by Matthew_Fiero (edited 08-11-2021).]
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Matthew_Fiero
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AUG 11, 07:59 PM
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Going by the previous thread the coolant routing should be okay. The connection on the modified thermostat and the connection under the snout.
I'm puzzled as to why coolant doesn't want to flow to the heater core .
Thanks to the contributions so far. I'm sure this can be figured out before the cold mornings hit! 
Matthew[This message has been edited by Matthew_Fiero (edited 08-11-2021).]
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Matthew_Fiero
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AUG 12, 01:10 PM
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Good Day Everyone,
I'd like to post some more information to maybe clear up the current state of the cooling system.
I am not utilizing the stock alternator bracket with the heater core lines as I have installed a low mount alternator solution utilizing the stock Fiero location.
I have 3 options for only 2 hoses
1. LIM (connected)
2. Timing Cover (capped)
3. Modified Fiero Thermostat (connected)
Thank you all again for taking your time to read.
Matthew
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