Is it the thermostat?

[warrenbh]

I'm driving on the turnpike in s florida today. the temp was around 90.

the temp needle slowly creeps way to the hot side in my 66 mustang, 289.

i pull off into a service plaza to look under the hood. I smell some coolant and it looks like some has left the overflow tube next to the cap. I open the cap to release some pressure and hop back onto the highway.

the needle quickly goes back to midway (normal reading). Slowly, over 10 miles or so, the needle starts heading back to hot, gets really close but never reaches it.

Do i have a stuck thermostat in the closed position? Or is this a water pump issue?

Thanks in advance,
Warren

 

[tx65coupe]

Sounds to me like the radiator cap needs to be replaced, if its letting coolant out. I'd fix that first.

Its hard to really say what is going on. You may have a bad thermostat from what your saying. Can you consistantly repeat this over the same driving time/distance etc?

This is just a thought, but maybe the sending unit for the gauge is acting up. I would get an infarred thermometer to check temps just to verify that its actually getting hot.

 

[2+2GT]

If the radiator is not belching coolant all over the place, the "hot" reading may not be accurate. You need to find out what the temp really is. A laser sensor, or even taping a digital kitchen thermometer to the upper radiator hose will tell you.

 

[Slobin3d]

you can pick up a direct contact IR temp gauge, they are very accurate up to 400 and since they are direct contact theres no chance of miss reading. also they are cheap $25

you should be able to pick one up at a Local hobby shop or TowerHobbies.com | DTXP3100 DuraTrax FlashPoint Infrared Temperature Gauge

 

[warrenbh]

Thanks for responding. Ok, so I get the temperature . . . and then what? Is there an acceptable/expected range?

 

[warrenbh]

I started her with the cap off and watched . . . . the coolant stood still and then surged up and out. I drove her in the city and the needle never went past half-point. The real heat seems to be on the highway . . . .

 

[mattchee]

I've been having a similar problem. Might know the issue.

I drove my 65 to work for the first time the other day, which is a 30 mi highway drive. My car ordinary has stayed cool as a cucumber on city streets and short highway drives around town. But, on this trip I noticed the temp creeping up and up. When I got off the highway, the temp regulated. I checked the coolant level before going home and it was low, so I thought that might have been the issue (in actuality it had gone out the overflow ). So I corrected that and drove home and had the same issue. I could smell the coolant, and it was low again when I got home.

I thought maybe it was a hose leak or a radiator leak cause the coolant had splashed around the engine compartment a bit (but that could have been the overflow hitting the fan). I resolved to run the car in the driveway for a while to replicate the problem and observe it. But in the driveway, everything ran fine. Ran it around the block a couple times, same thing, no problems.

I can't say definitively that this is the issue, but I did a little research and found out that for this particular symptom (overheating on the highway, but ok off the highway) is often due to the lower radiator hose missing its spring. Apparently without the spring, it collapses at highway speeds. I felt mine, and it definitely has the spring (how anyone could lose that is beyond me) but it does not cover the whole length of the hose, so maybe its collapsing, or severely compressing in the small areas that are lacking the spring. I'm probably going to replace that hose and see if that helps.

Anyhow, sounds like you're having a similar issue, so I thought I'd share that with you. In fade it helps.

If anyone has further insight into my issue, I'd love to hear that too!

 

[jonbacon]

YOU CAN ALWAYS GRAB THE RETURN HOSE AND IF ITS NOT HOT LIKE THE FLOW HOSE THEN YOU KNOW YOUR THERMOSTAT ISNT OPENING,, CHEAPEST QUICKEST WAY TO FIND OUT..

 

[Hack]

SNIP
I can't say definitively that this is the issue, but I did a little research and found out that for this particular symptom (overheating on the highway, but ok off the highway) is often due to the lower radiator hose missing its spring. Apparently without the spring, it collapses at highway speeds. I felt mine, and it definitely has the spring (how anyone could lose that is beyond me) but it does not cover the whole length of the hose, so maybe its collapsing, or severely compressing in the small areas that are lacking the spring. SNIP

THIS.

 

[warrenbh]

Hey Mattchee,

I got the thermostat replaced (it needed replacing by the looks of it) and still I have the same issue. The inside of the radiator looks a bit clogged so I'm going to switch it out and install lower hose with spring.

Thanks for the suggestion, will give it a try!

Warren

 

[rbohm]

if the thermostat fails in the closed position, the engine temp will not slowly creep up at speed, it will shoot up fairly quickly. it sounds more like to me that the radiator needs a good cleaning, or rodding out, to clear the tubes.

 

[mattchee]

Hey Mattchee,

I got the thermostat replaced (it needed replacing by the looks of it) and still I have the same issue. The inside of the radiator looks a bit clogged so I'm going to switch it out and install lower hose with spring.

Thanks for the suggestion, will give it a try!

Warren

Let us know how it works out. I'm going to replace my hoses and see how that goes for me. If the problem persists I'll move on to the radiator...

 

[Couped Up]

Just out of curiosity.... Are you running pure coolant, or mixed? also, what type of engine build do you have, and T-stat temp? Are you using other than stock pulleys?

 

[warrenbh]

It's the Spring!

Mattchee,

You're the man. I flushed the radiator and engine, and put a spring inside the lower hose. I had trouble sourcing the spring, I ended taking it out of a "flex" hose supposedly designed to "fit" as lower hose. This hose really doesn't work because it bends and creases when you install it. Luckily it had a spring that I could easily remove and use in the existing hose.

I ran her considerably on the highway and the needle didn't budge past the halfway mark! I'm going to add Water Wetter too and see . . . .

Thanks for the suggestion, without it I would have been in the same spot for a long time and after spending mucy $$ on radiator and water pump.

Thank you Hack for the confirmation.

Couped - I've got a 289 4bbl with modified cam, 180 T-stat and am running an even mix.

Thanks everyone!

Warren

 

[mattchee]

Awesome! Glad it worked out!

 

[Couped Up]

gotta love those inexpensive fix's!

 

[Hack]

I'm glad to hear you solved the problem.

 

[65ShelbyClone]

Apparently without the spring, it collapses at highway speeds. I felt mine, and it definitely has the spring (how anyone could lose that is beyond me)

One possible scenario is the spring corroding and falling to pieces from owners using the wrong coolant mix(like straight water). The original engine from my '68 had been run with straight tap water for so long that the timing over had holes in it.

 

[Stangninjak]

Hmm I tyhink I need to check my lower hose. I seem to run at 210 or so...but I am also running a 351w built up..I had a 180 temp in and now I went to 160...