Big BB temperature fluctuation

[KobraKarl]

Blue sky again today so I went for a spin and noticed again that my engine temp is very unstable.

I have been overlooking this due to more pressing mechanical needs, but I am wondering whats the deal ,and is this just part of the bastard cooling systym of the cobra BB ?

I understand that in heavy traffic or hot weather of course it is going to run hottish, but on a 60 deg. day at 40 or 50 mph the temp wont come up over 150 deg. unless Im stopped a while and then it will fairly quickly heat toward 190 to 200 if I dont hit the fan switch.so back and forth goes the temp all over town.

I'm concerned that this constant temp cycleing may be a little hard on the engine, or is this the way it is for you too? it has a new 180 deg, stat.

thanks Karl

[mr0077]

Karl, I'm about to tell on myself, but check this: pull the housing and confirm that the copper button on the T-stat is facing the engine block. I put one in backwards and at speed the pump blows the T-stat open no matter what the coolant temp, at low speeds it doesn't sense the correct water temp and opens late...talk about feelin like a dumba$$...oh, well, cheap check and fix...just cost a T-stat gasket.
Let us know what it is.

[Rick Parker]

I had a problem with severe temprature fluctuation that was solved only by changing to an OEM Ford water pump with cast iron impeller. The stamped steel impeller that was in the one I had bought at the local parts house was causing cavitation at speed. Temp would spike at 230 then slowly return to 160 then take off quickly to 230 again. This would repeat itself constantly once the thermostat opened. May apply to your case too???

Hope this helps

Rick

[decooney]

Karl,
some may have other ideas, but here is where I ended up to finally resolve this living in toasty California during Summer months.

- Be sure you don't have air trapped in your system! Critical.
- Best Monster fan money can buy (stop/go requires FANS!)
Note: some guys use push and pull. At least a big puller fan.
- Proven high-flow aluminum water pump
- Quality high-flow Aluminum Radiator
- Not too much anti-freeze, just enough for corrosion.
- Distilled water only & Water Wetter during Summer
- Change water before/after each summer/winter season
- Automatic Fan switch in-line, kicks on at 175 degrees
- 160 hi-flow thermostat during hot summer or frequent traffic
- Frequent oil and oil filter changes, using good 20/50 oil only
- Engine timing not too retarded/adv. 10btdc init, 35 total.

These are just my guidelines. Some may disagree, but it works for me for my FE. Give a new FE time to break in if its new. Also, make sure you don't have any vacuum leaks somewhere. Check your carb to make sure the Primary is not jetted too lean or adjusted too lean for the idle circuit. To me, keeping the idle too low does not help oil or water flow in traffic. Good Luck.

[KobraKarl]

Ken, will check

Rick , I just put in an Edlebrock hi perf ( whatever that means)

Duane,

Got a big puller fan
got a nice new water pump
timing is well advanced(maybe a touch too much)

thing I dont understand is why it wont maintain the heat at speed (drops to around 150) then pops back up at every light I was just thinking it should be more stable,I really havnt had too much trouble keeping it cool.

[dalola]

KobraKarl,
These are all very good suggestions. While you are taking things apart, pull the thermostat out, and verify it's accuracy in a pan of water, on the kitchen stove. Put an accurate thermometer in with it, such as a meat thermometer, and verify it's opening temp. as compared to the thermometer. Also, verify your gauge is accurate, and take into account your sending unit location. This can also effect temp readings. If everything is functioning properly, your engine should not operate much less than 10 degrees below the thermostat opening temp., at it's coolest point.

Good luck!

Dave

[Mr.Fixit]

If your engine is running cooler than the thermostat, than the thermostat is not preventing the exchange of water between the engine and the radiator. Did you do the old trick of drilling a small hole or two in the thermostat, if you did and they are too big, this will happen. It is possible you accidently got a 160 thermostat, try the pot of hot water trick in your kitchen to find out if it is opening too early, or not closing completely.

[427 S/O]

KobraKarl, mr. fixit is right about the small hole in the top of the thermostat, 1/8 is what I drilled with no problems.