Thermostat doesn't seem to open properly

[edcreed]

hello all...and thanks in advance for the help

I've had the same problem for a while now. It seems that my thermostat (and new thermostat) do not open until I manipulate the hoses and let pressure off of the radiator cap. Every cold start I have to do this before it opens and allows water to flow freely. If I don't do this, the temp just continues to climb until I do and obviously the fan won't come on because the thermostat didn't open and the bottom of the radiator is cold. The fan only comes on after I do this and start to feel warmth in the bottom hose.

I've read all about the air bubbles and raised the front of the car and have burped and burped and put the T in on the return line over the head and disconnected the heater and all that good stuff, but can't seem to figure this out. I feel certain that I've worked all the air out of my system multiple times...fyi, I've replaced the water pump (two weeks ago), stadt and all hoses and had the radiator cleaned up and repaired by the radiator shop and also replaced the fan temp switch at the bottom of the radiator and the temp sending unit on the head.

any suggestions or thoughts are welcomed.

It's a 1980 124 FI
thanks again.

[RRoller123]

Bad (sticking) thermostat?

Maybe it is improperly installed? It is possible hose it up incorrectly.

[edcreed]

hey Roller, thanks

here's a pic of the thermostat on the car...

As for a sticky thermostat, I was kind of thinking since the one that was on it when I bought it and the new one behave the same way that was most likely something else causing it...and I keep coming back to air bubbles, but I feel certain I'm following the recommended burping procedures. I even had the guy at Vick walk me through a tutorial since I live 5 miles from Vick.

I should probably add that I bought the car when the PO had a blown head gasket. The PO was a regular poster on this forum (Foster48x for you longtimers) and seemed to know a lot about these cars...but I'm thinking he was probably having the same issues I'm having and that's what caused the head gasket issue.

[RRoller123]

Yep that looks to be hooked up correctly. Maybe pull the T-stat and test it in a bath of boiling water (NON POTABLE pan). Bring the temp slowly up and test with a simple plumber's thermometer (avail at HD) and make sure it opens at the proper temp. (~180 F or so)

If the T-stat is good, sounds like there is air trapped in there. Maybe the Union at the front of the engine is backwards? The small hole needs to go toward the LEFT. That is a stretch though, as it would likely lead to overheating if in backwards.

Possibly radiator needs flushing and is not flowing properly?

[klweimer]

This is my favorite for getting all the air out of the system. Works great.
https://www.amazon.com/gp/product/B001A ... UTF8&psc=1
Attach this to the radiator and start the car. Put some extra antifreeze in the funnel and keep tapping all the hoses (don't forget to put the heater on max heat) while everything heats ups. Everything burps up through the antifreeze in the funnel.
Kirk

[So Cal Mark]

continually getting air in the system is one indicator of a leaking head gasket. Test your old thermostat with a hair dryer, it's easier than boiling water

[RRoller123]

continually getting air in the system is one indicator of a leaking head gasket. Test your old thermostat with a hair dryer, it's easier than boiling water

That's a good idea, you don't ruin a pan either.

[edcreed]

Well, I drove it home from work yesterday which consists of about 10 minutes of city (stop and go) driving and then 20 minutes of 70 mhp wind in your hair driving and it ran like a champ and never moved from 190. But in my defense, it's done this before and then the next day it will go back to having issues.

I have a similar setup for burping klweimer, but I think I'll buy that one anyway, it looks better than mine...

and I will certainly test my old thermostat...I did that once and thought it was working properly...but I think I'll do it again to prove it to myself again and maybe post pics of that to make sure I know what I'm looking at.


So Cal Mark wrote:
continually getting air in the system is one indicator of a leaking head gasket.

Is there any way to test for this? I've not seen white smoke and it's running really smooth and doesn't seem to have lost any power...I was on the highway yesterday and was considering passing someone in front of me that was swerving around, so I looked down and caught myself running about 85 mph already, so I just decided to back off...so the point is, it's running pretty good.

Maybe the Union at the front of the engine is backwards? The small hole needs to go toward the LEFT

Roller, I'm not sure what this means but if it helps, here's a pic I took when putting it back together...not exactly the current state, but close.



Thanks for all of the feedback...

[RRoller123]

That T junction at the top front of the engine where the 2 hoses and the sensor all meet? That can be put on backwards. Inside it has a restrictor hole, smaller on one side, and it (smaller restrictor hole) has to be to the LEFT in your picture. I.E. To the Left when you face the front of the engine. Unfortunately it is a pita to check, as it means draining the system, but if you are going to pull the T-Stat anyway, you might as well check this T just to be sure. It is VERY easy to put it on wrong, it is entirely symmetrical outside!

[klweimer]

RRoller123,
I don't think the T is symmetric. The connector on the front points down and the bleed screw points up (at least on the FI models). If you flip it 180 degrees, everything will be pointed in the wrong direction. Right?
I did notice this car has an extra stop cock on the T, don't think that's standard...
Kirk

[RRoller123]

The holes are the same thread, so the sensor or bleed cap can go in either one.

[edcreed]

I was thinking the same as Klweimer on the positioning of that T...but the next time I drain it and check out the thermostat (and drill the small hole in it that I've read about...although, the old one has the hole in it and that didn't seem to help.), I will check the flow direction of the T.

I also read that another post that said they capped off one side of that T, removed the external thermostat and went back to the internal thermostat and went straight from the bottom of the radiation to the water pump...that seems to make a lot of sense in my brain. I don't remember who it was, but what do you guys think about that? Is that an option?

[klweimer]

Good point on the vent plug and the sensor. I wasn't thinking about them being uninstalled from the T housing.
Kirk

[So Cal Mark]

Fiat went to the external stat on the larger motors because they flow more than the internal stat. If you switch to an internal stat, you're eliminating the bypass function so that water circulates when the stat is closed

[rridge]

The best in-head thermostat for a Twin Cam engine is a Stant Superstat 45358. Flow capacity is ample and it is self venting to eliminate air bubbles in the stat chamber. The same stat is used in Chevy small blocks. The problem on 1975 and up carbed engines is that they have a water heated choke and no bypass means no circulation to the choke until the in-head stat opens. On the FI engines with the FI temp sensor in the tee, eliminating the bypass flow means an incorrect temp until the stat opens.

The best way to convert an FI engine to in-head stat is to move the FI sensor to the location used on the FI Brava in the head. That requires giving up the over-temp switch that uses the middle head boss. The Spider is the only Twin Cam that mounts two temp senders for the gauge. The temp gauge works normally with the overtemp switch disconnected. The head mounted FI temp sensor works normally without the need for a bypass flow.