Hello.

Having some trouble with the cooling system on my swap. After running for several minutes, the upper radiator hose is still cold, the lower hose and the heater hoses are hot and the coolant overflow bottle starts to fill up and overflow. It appears that the thermostat isn't opening at all, and coolant is bypassing through the heater core and never making it to the thermostat. The temp gauge never moves off cold.

Here's my setup:

0 mile LQ1 crate motor in 91-93 configuration. Motor has only been started a handful of times.
Hoses routed in the factory DOHC manner

• lower hose in at the water pump, upper hose out at thermostat
  
• heater hose in at fitting on water pump housing
  
• bypass hose from water pump housing to upper intake manifold
  
• heater hose out at fitting in lower intake

I'm using an in-hose filler that is the highest point in the system (higher than the heads). I have added an air bleed in the bypass hose at the intake. It is at the same height as the filler.

The Fiero temp sender is in the head in the stock DOHC location. I used a 1/4" elbow and a 3/8x1/4 reducer to install the sender upside down off of the head to clear the exhaust. (I pulled it to see if it was getting coolant there and it was wet.

I'm thinking I either have air in the system, the thermostat is stuck, or the radiator is clogged (it's a used V6 unit). I am using the air bleed, which seems to be working fine. I pulled the thermostat and tested it in a pan of water on the stove with a thermometer. It works like it's supposed to. I double checked my hoses, bled, burped and even used a vacuum pump to make sure the air was out- but the problem persists. I'm using a stock DOHC thermostat (195 degree) and the engine is stock.

I'm also planning to make an in-line adapter for the temp sender (tee with hose barbs) and put it in a heater hose. This won't give me the most accurate info, but it's better than nothing.

Any ideas? (Sorry for the long post)

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1986 SE Aero coupe.

3.4 DOHC swap is complete and running, now just have to finish the rest of the car...

Monday morning bump.

I don't know much about the DOHC, but it sounds like the heater core/bypass isn't anywhere near the thermostat. (Unless I misread your post.)
You've got to find a way to get hot coolant to circulate past the thermostat, or it will never open.
If nothing else, drill a small hole in the thermostat to allow circulation.

Here's my hose routing scheme (minus the oil cooler). It's the same way the DOHC is plumbed from the factory.

Not really understanding how you can clip a bit off the edge of the thermostat.
Most drill holes around the outer edge of the base just inside were the rubber gasket sits.
It almost sound as if your pump is not turning or you have a blockage.
After you clipped a bit off the edge of the thermostat did you re boil it to insure your modification
did not impede the function?

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Red 1988 GT 5 speed
Poly all around, Koni's & Lowered
LQ1 powered
3800 swap in progress
http://s733.photobucket.com/albums/ww339/CC_Rider/

Yes, it still works fine. I clipped a bit off of one side so the outer shape is that of a circle with a flat spot. (sorry, no pics). That created a small, D shaped opening about 1/16" wide When installed) that will allow air to escape. I also realized that I used thread tape on the fittings that I used to adapt the temp sender to the head, probably insulating it from ground and rendering the sender inoperative. I'll fix that and then see what's up. I'll also double check the radiator to see if it's flowing OK before I fill the system back up,

Does it run cool with the thermostat removed?

Haven't tried that yet.

dumb question, you dont have the water pump running backwards do you?

not a dumb question
see it happen before and I was the one who missed it.

edit to add a link for belt routing just incase
http://www.justautorepair.c...ory/1-belts-diagrams

[This message has been edited by CC Rider (edited 02-11-2013).]

quote Originally posted by FieroReinke: dumb question, you dont have the water pump running backwards do you?

No. The belt can only be run one way on this engine. There is a raised area on the timing belt cover that forces you to install it correctly. I did verify that the pump is working. It's all brand new GM, so it better work...

quote Originally posted by tesmith66: The Fiero temp sender is in the head in the stock DOHC location. I used a 1/4" elbow and a 3/8x1/4 reducer to install the sender upside down off of the head to clear the exhaust. (I pulled it to see if it was getting coolant there and it was wet.

When I had first bought my DOHC swapped Fiero last year, I had a lot of trouble getting the temp gauge to work. I discovered that the PO that did the swap had actually drilled and tapped the hole in the head to match the Fiero temp sender's threads, and used the stock Fiero temp sender. I replaced it with two different brand new units and it just would not work. It could idle for 20 minutes and still wouldn't register on the gauge. Once I started moving, I'd get a block down the street and it would quickly rise past the red on the gauge. I would come back home and park it and it would drop back down to cold within a minute or two.

I finally ended up using the stock DOHC temp sender, with a pipe reducer so that I could thread it into the head properly. Once installed, it worked perfectly, as did my cooling system. (whew!) I don't know why the Fiero one wouldn't work, but once I switched to the DOHC unit, everything was great. This may explain why yours is not registering on the gauge, I would try the stock DOHC one out. That, and yours may not be getting enough coolant flowing past it the way it is mounted out of the head.

Of course, this doesn't explain your other issues though. It also took me a very long time to bleed all of the air out of the system, which I'm suspecting is partly due to the routing of the heater hoses and I plan to fix that this year. I'd try it without the t-stat completely just to rule that out, and make sure to get all of the air out. Everytime I thought I did, I would find more in there and have to bleed it again.

Hope this helps...

[This message has been edited by Silicoan86 (edited 02-11-2013).]

So, what I learning is this engine is a real bear to bleed. I'm tempted to drill through the upper intake into the throttle body heater passage and put the bleeder there.

I wasn't aware that you could open the hole in the head up to 3/8 NPT. I was afraid to try it.

I know my temp sender works, because it worked fine on my V8. Also, the factory DOHC sender is just a switch, right? Does it actually work the gauge correctly, like the Fiero one is supposed to?

quote Originally posted by tesmith66: I know my temp sender works, because it worked fine on my V8. Also, the factory DOHC sender is just a switch, right? Does it actually work the gauge correctly, like the Fiero one is supposed to?

Chances are, between the three Fiero senders I used (two of which were brand new), at least one of them was good. The DOHC one works the gauge perfectly, the only thing I'm lacking is the additional wire that controls the warning light since the DOHC sending unit only has the one wire for the gauge. IIRC, the stock w-body temp warning light is controlled by the ECM, not the sending unit like the Fiero. I have yet to be able to figure out where to hook the warning light up to the ECM.

[This message has been edited by Silicoan86 (edited 02-11-2013).]

Another silly question, are you putting the thermostat in correctly I.E. with the bi metal spring on the bottom? It has to sit in the coolant flowing in the heads to heat up and open. Do try running without the thermostat to see if the coolant is actually flowing.

Joe Sokol

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85 SE Daily driver with a 3.4 DOHC OBD II
88 Formula/GT 4.9 Allante Intake (My Baby)
www.fieroking.com

Yes, the thermostat is in correctly.

After thinking about it and reading the responses, I believe I am still having an air bubble issue. This engine bypasses through the heater hose that is in the thermostat housing when the thermostat is closed. If there is an air pocket in there, the coolant will run through the heater hose fitting without ever coming into contact with the stat. I hope the opening I made in the top of the stat will allow air to escape and enable a full fill of the housing.

I also am going to replace the radiator cap up front.

NEXT QUESTION:

I have an in-line filler at the engine with a standard rad cap on it. Do I need to replace that with a non-vented cap? Currently I have 2 vented caps in the system. Is that bad?

quote Originally posted by tesmith66: I have an in-line filler at the engine with a standard rad cap on it. Do I need to replace that with a non-vented cap? Currently I have 2 vented caps in the system. Is that bad?

The rear cap should be 2-3psi higher vent pressure (so the front one opens first), then seal the vent passage on the rear one (if it had one). I ran an inline fill on my Ramjet setup and never had any issues with it setup like described.

The sender in the front head will operate the Fiero temperature gage correctly. Just from experience I would recommend taking the thermostat housing and the thermostat out and filling it up below where the thermostat sets on the manifold until it's completely full. Then putting everything back together and filling up the rest of it to the highest point possible. Then run it. If it gets hot after that shut it off open the bleeder screw let the steam vent till coolant comes out shut let it cool down a little bit and then rinse and repeat as necessary. You can speed up the process by squirting cold water on your engine and the radiator. Unless you have a bad radiator it should work itself out.