C. Ludwig

iTrader: (27)

I have an FD in the shop that is busting my chops over a consistent air bubble in the TB thermowax. The car was brought to me with a high idle which I tracked down to the air bubble. The thermowax stayed cold when the engine was fully warm.

I pulled the coolant feed line off the TB and filled the system to purge the air. I have a Lilse funnel and combined with jacking up the front of the car it allows me to get the coolant feed at a higher level that the TB to push the air out of the system. The coolant will flow from the hose out of the rear iron just fine but it doesn't want to flow up through the TB and out the barb even if I hold the hose off the rear iron higher than the TB. I can plug the hose off the rear iron and only get a trickle out of the TB.

I disconnected the return hose from the TB at the back of the water pump and blew air through the TB thinking there was a blockage in the line somewhere. I got a little bit of coolant out and the air seemed to flow fine.

I ended up connecting another hose and funnel to the TB and pouring coolant through the TB and watching for the air to be purged through the coolant filler.

Re-assembled everything after watching the trickle (all I could get) of coolant flow out of the TB and getting a good stream out of the hose off the rear iron. Started the car and let it warm up fully and the thermowax did actuate lowering the idle to where it should be. So all is well...

Problem is that when the car cools the coolant level falls as it contracts from cooling and the air bubble re-appears in the TB and we start all over.

Two questions - Why am I not getting a good stream of coolant out of the TB when the hose is disconnected? Nothing is kinked and I can blow through the line so there is no restriction. Secondly, how to prevent the air bubble from re-forming in the TB? The car has an aluminum AST and all new hoses that are properly installed. It doesn't lose coolant from regular use. ???

Gadd

There is a lot of flow thru the tb coolant line I don't think air is the problem, I'd pull the thermostat and see if it's stuck open. Does the plunger on the back of the thermostat block that passage when open? I can't seem to remember if it does.

C. Ludwig

iTrader: (27)

I used a propane torch with a low flame on the thermowax to bring it open when I was trying to bleed it thinking that it may block the flow of coolant when cold but it didn't make a difference.

Gadd

I meant the cooling system thermostat not the thermowax..............

DaveW

Sounds to me like you're not sucking coolant back from the O-F tank (bad AST cap, leaky hose to the O-F tank, etc). The basic problem is that the air bubble re-forms when you shut the car off and it shouldn't. IMO, once you get rid of the air bubble, you should be OK.

CantGoStraight

The thermowax unit is nothing more than a some what restricted bypass for coolant to flow over a temperature activated plunger. The coolant doesn't flow into the plunger and can't be restricted by anything other than debris. I have had them apart and can post pictures ot it if your interested. Jack
Ps. the restriction goes from the metal tube to a hole the size of aproximately a number 7 drill. (I believe that's what I use for making the gasket.

DaleClark

iTrader: (55)

Yeah, I think the problem lies in the coolant recovery system. I've NEVER had trouble getting air out of an FD's coolant system - just pop the hose off the throttle body, fill everything, good to go. I haven't had to jack the front up, use the funnel, etc.

A pinhole leak in the rubber line from the AST to the overflow tank can keep the system from creating a vacuum to suck coolant back from the overflow tank on cooldown. Either that or a small leak in the cooling system somewhere that's sucking air back in.

I have also seen thermowaxes that were just rusty and would stick easily, too.

Dale

C. Ludwig

iTrader: (27)

OK. Thanks for the replies. I now have a few things to check at least. The restriction in the thermowax explains why coolant doesn't "flow" from the fitting like it does out of the hose off the rear iron.

CantGoStraight

I would think that if you plug the hose comming off the rear iron (attaches to the top of the TB) tha if you squeeze the radiator hose you should get a pretty good squirt. A number 7 drill bit ais pretty close to a 1/4" hole so you may actually have some blockage that needs looking into. Thats something I've done when purging the air out of my cooling system (plug each side till I get fluid out of them then hook them back up) that leaves a very small air bubble in the hose. Jack

C. Ludwig

iTrader: (27)

The problem ended up being the pressure cap on the AST. It wasn't allowing the coolant that was pushed out to return when the engine cooled. Changed the cap, bled the system and all is well.