Thermostat Housing and Cover Problem

[stevef1972z]

First the back story:

Bought the 1972 240Z one year ago this weekend. Blew a head gasket getting it home. Replaced the head gasket and drove the car a bit and discovered brake issues, fixed those and discovered that the frame rails at the T/C mount were rusted completely away, fixed those and frame rails and floor pans. Thought I was set to drive.

Drove a bit, (3 miles) no problems, drove a little more (about 7 miles) and it started getting hot. Guage was more than three quarters pegged. Searched here and figured I needed to do some work as there are overheating issues with some of the cars. Starting simply and working my way up, I started with a new radiator cap and a flush and clean of the radiator and block. I also removed the AC condensor to add more airflow and added and overflow tank. No improvement. This morning, new thermostat was in the mix. Promptly went down, set down my coffee, and proceeded with very light pressure to break both bolts on the thermostat cover! Took the thermostat housing off of the engine, got it out where I could work on it, and after drilling pilot holes, and trying the easy outs, I managed to break the bolts both lower and even with the top of the thermostat housing. Cannot get them out of there, they are chemically bonded for life!

Did get the cover off, and the shaft of the thermostat housing, where the stopper slides up and down was bent! By the condition of the bolts, I would say it had been in there for a very long time, and may be the problem with the overheating.

I need two things from you all:

1) Why would the shaft of the thermostat itself bend, what is the failure of this part telling me, is there a larger problem? I have never seen this type of parts failure.

2) Does anyone have a thermostat housing, cover and housing would be good, or just the housing that bolts to the engine would work as well?

Thank you all in advance.

[Diseazd]

You can buy housing, cover and bolts from Motorsports.....800-633-6331

[Walter Moore]

I had to actually drill out the broken bolts, which is a very delicate operation involving drilling a plot hole, and then enlarging it slowly with ever larger drill bits until I could peel the old bolt out of the housing.

This is a dangerous operation if you intend to keep the housing because the bolt is steel and the housing is aluminum. One slip and you ruin the housing.

The corrosion is because the metals are different and in the proximity of water.

Oh, and by the way you should do a search on overheating in the forums. The temperature gauge reading 3/4 is not abnormal on the early Z cars. This has been discussed at length, and there is a lot of really good information here. It is way more than I have the time to try to summarize this morning.

Good Luck!

[Diseazd]

Drilling out aluminum is tricky.......a good machine shop can put heli-coil insert threads in.......better than new and low cost!

[stevef1972z]

Thanks. I thought the housing would be harder to find. It was a panic post!

Ebay, motorsports and I think the dealer still have access to them. It seems lots of folks dont use anti sieze when working on these parts.

What still has me confused is why the thermostat shaft bent. I hate throwing parts in the car when I cant figure out why the old one failed. At three quarters and a bit more on the guage with a spread between numbers of 120 to 250 at three quarter it was running around 220* F and still climbing, that is way too hot for my tastes and it was in the very low 80's here that day, rare for this time of year. I want it running cooler so I watch the road more than the guages so I can enjoy it without fear. Rad is goig up to get tanked and rodded, new waterpump and it looks like a fan clutch rebuild as well. Looks like I am stuck waiting on shipping of the housing, so I will wait it out and work away.

[Z train]

One thing i've done is use stainless studs & nuts to hold the housing to the head.

Second is i've powdercoated every square milimeter of the housing and cover.Third-i've drilled a 1/4 inch hole in the T-stat body.I've done this on my Z,my 810 daily driver and my wifes 620.

Cut the center out of an old T-stat and run that for a test.If nothing changes,your problem lies elsewhere.Odds are it's the radiator all other things being equal.

[Diseazd]

Faulty from the factory is my bet......there ain't enough pressure to bend it. Put it back together with a new thermostat.....then try it. If that doesn't fix it, go forth with radiator etc. Don't just start replacing stuff, that gets expensive. I don't blame you on the gauge....all my Z's (3) run dead in the middle and that's in a hot Virginia climate.....3/4's doesn't get it!

[Diseazd]

They're all 180 degree thermostats also.

Edited July 5, 2009 by Diseazd

[Z train]

Test the T-stat beforee installation.I've had 4 bad ones in a row from different sources.

[stevef1972z]

Swapped out the waterpump today, it was rather full of rust, and did not spin smoothly. New one is in, and the RTV is drying now. Ordered my thermostat housing and thermostat, so I will install them when they get here.

I still cannot figure out why the thermostat bent, just doesnt seem right.

Does anyone have the temperature sensor parts number, I would like to replace it as well since I figure it is the one that came with the car from Japan like the waterpump and the thermostat!

[240Z-Fan]

I still cannot figure out why the thermostat bent, just doesnt seem right.

As I recall, the thermostat has to be oriented a specific way to fit in the housing, if it isn't you will either break the housing (BTDT) or bend the thermostat.

My guess is that it was bent during the installation by the previous owner/mechanic.

(So pay close attention to the orientation and fit when reassembling.)

Al

Edited July 6, 2009 by 240Z-Fan

[stevef1972z]

The new thermostat housing came in the mail today. It is resting comfortably under the hood now, and the RTV is drying. New thermostat is in place, upper and lower hoses have been replaced and the new water pump is nestled at the front of the engine. Inside the rad is a super flush kit that will need to be run about 10 or more miles through a few heat cycles to clean up the rest of the system.

The fan clutch seems fine, and passes the cardboard test listed in the posts, so it was just cleaned up and put back on. I will update Friday or Sat after I get the flush through the system good, and see if I fall in the cool catagory.