Problem with over heating

[Wayne Maybury]

No, not my Cobra, it never overheats, but I do have a problem with my '66 Mustang.

I recently restored a '66 Mustang coupe that has a 289 and a C4. I had the engine rebuilt even though it was in good shape, changed the water pump, the thermostat (twice), the cap on the rad, etc. The engine now has flat top pistons, a mild Comp cam, an aluminium intake with a new 600 cfm Holley, and headers.

Here is the problem. The engine comes up to normal temp and runs at that level for a while (half an hour or more) then if I push it a bit harder on the highway or get stuck in traffic, the temp goes up by about 15 or 20 degrees and stays there. It does not come back down once the car is moving normally again. I figured that the thermostat was sticking so I changed it and went down from a 180 to a 160. Now it runs cooler but will still go up by about 20 degrees the same as with the 180 thermostat. I have the original temp gauge so I cannot say exactly what the temp is but the increase is quite significant.

The level of the coolant does not go down so there are no leaks and it doesn't boil over but it did puke out coolant when turned off until I changed the rad cap to a 16 psi. The radiator came with the car but it looks like it is new, the hoses and fan belt are new or in very good condition, and the pump was changed when the engine was rebuilt. The coolant appears to circulate well but of course I can only look when the engine is relatively cool. I have tried both a regular fan and a new clutch fan with no differences. It always does the same thing even if the outdoor air temp is relatively cool. It is no better nor no worse if the air temp is hot or cool.

Does anyone have any idea why this engine will run at two different temperature levels? Normally engines that heat up in traffic will cool right back down as soon as the speed picks back up. I have thought about buying a new aluminium direct replacement radiator from Summit but I am not even sure if that will help or not.

Wayne

[mrmustang]

Wayne,

The first question I have is "are you running a fan shroud"?


Bill S.

[sharpe 1]

Check out your temp sending unit and also check gage for proper operation.The fan shroud is also required for proper operation.

[Wayne Maybury]

Bill

I indicated that I was thinking of buying a new rad but I forgot to say that I was also considering adding a shroud. I believe that old Mustangs didn't have fan shrouds unless they had A/C. This car came from California but was not equipped with A/C so it does not have a shroud. Mustangs Unlimited have them for $34.95 plus mounting brackets. I think that you are hinting that this would probably be a good place to start.

Wayne

[double ugly]

I am no expert, but I've always believed that a car with a higher temp thermostat will run cooler. I never run less than a 195. It gives the radiator a chance to cool the water when the thermostat is closed.
John

[badrich]

When I installed my new motor it overheated when I was stuck in traffic. A custom shroud, along with a puller fan and Water Wetter solved the problem. Rich

[mrmustang]

Wayne,

All original Mustangs (even 6cyl) had a shroud of some type.....These are imperative for ducting air pulled through by the fans in order to properly cool your engine. If the radiator is new, then you might want to check the upper and lower hoses for internal springs, if the springs are not within, then under pressure the hoses could be partially collapsing, restricting the flow of coolant and causing your engine to run hot. If the coolant (you are running a 50/50 mixture of coolant and water correct?) is muddy, or even brown in color, then your engine may need to be flushed and or your radiator may need to be replaced......

Bill S.

[Rick Parker]

I had a situation somewhat similar and determined that the "new" water pump which had a stamped steel impeller (aluminum, early type pump without backing plate) was cavitating. I replaced it with a OEM Ford rebuilt unit with a cast iron impellor and all was good from then on. Symptoms were that the temp gauge would spike and then swing down low to about 140 then quickly (in seconds) up to 220+, back and forth.

[Wayne Maybury]

Firstly, the shroud is on order from Mustangs Unlimited. I should have it by the weekend.

Secondly, yes I am running a 50/50 blend of antifreeze and water. The coolant is new so it is clear and a nice yellowish-green colour. However, I just looked inside the radiator and saw that some of the tubes appear to be at least partially gummed up. I had never noticed this before. I am going to go get some rad flush and clean it out tonight. While the rad looks brand new from the outside, it maybe dirty on the inside resulting in restricted flow through some of the tubes.

Thanks for all the input. I will let you know how this works out in a couple of days.

Wayne

[mrmustang]

Wayne,

Take your radiator out of the car and drop it off at a proper radiator shop and let them hot tank it for you. Their solution will work far better than anything that you could buy off the shelf. Also, when you get it back, if you are going to paint it to make it look better than it does after being in the hot tank, remember to only use light coats and not to spray it on too heavy.....Don't wait, do it now!!!!!!!!!!!


Bill S.

[Wayne Maybury]

Bill

Thanks for the advice but I had already purchased a can of rad flush and started doing it before seeing your post. I spoke to a local radiator shop last year about cleaning my gas tank and he told me that they are now greatly restricted in what they are allowed to use for cleaning gas tanks and rads so that may no longer be a great option. If I continue to have difficulties, I will take the rad there to be cleaned by them however. I have never been a believer in putting lots of paint on a radiator as it will simply act as an insolator when you actually want good heat transfer.

I dumped my antifreeze, put the rad flush in, ran the engine, dumped it out, refilled it with clean water, ran the engine, and repeated this several times until the water came out perfectly clean. I looked in the rad and it sure appears to be much cleaner than before I started. I refilled it with a 50/50 blend of antifreeze but I haven't driven it yet.

Wayne

[mrmustang]

Add to your mixture a can of Motor Max (or equivilent water wetter) to play it safe. If you still run into issues, await the fan shroud and go from there.

Bill S.

[MY 401K]

You might want to think Water Pump Pulley Diameter. The smaller the diameter the quicker it turns. That cured my problem.

John

[Bill Wells]

the temp gauge may be the real culprit as well as the level of antifreeze in the radiator....it might not be as hot as you think it is and perhaps is slightly overfilled and while not puking fromo the cap, the overflow is trying to tell you to let the level go down.

i have a modified K code 289 in my 65 mustang convert, bored .040 over ( 294.3 cubes ), built to shelby gt 350 specs with addition of crane alum roller rockers, 715 lemans holley and tremec 5 spd with 3.89 limited slip rear end . tri-Y headers and aluminum intake and oil pan. cap is 15# or 16# ( car is offsite now so i cant check it ).

my old stock temp gauge would peg to H but nothing would puke out of the radiator, but overflow would spittle some when stopped . i have the hi-po standard radiator shroud. i added a 6 blade clutch fan, no change in stock temp gauge reading. i finally added an aftermarket temp gauge ( with numbers instead of H or C like std gauge ) and lowered the rad fluid to just above the core in the radiator. anything more and i still get spittle out of the overflow, but if just to the top of the core i get NOTHING. fluid is fresh and 50/50 mixture .

temps run about 190 -195 F in traffic and 180 or so otherwise, unless ambient temps outside are 90 + F . at least now i know what the temps are vs H or C reading guesstimates and confirmed that the old tired stock gauge was innacurate and giving me false readings of being H when it was still in the ok zone in reality.

as i was told by some friends ; if it isnt puking it is not hot ...might be some seat of the pants logic there.

btw , my 57 bird does the same thing re overflow tube spittle if rad is filled above the core. . odd coincidence perhaps, but little birds were hot running engines anyway. old gauge there would peg H prematurely too. I added a 10 ohm resistor and voila, tricked the gauge to showing lower temps , so now if it is really hot it is at H and not giving me an early warning of saying it is H when it really is not.

Bill.

[Dwight]

We have solved the over heating problem in three Cobras ( 5.0, 408 & 427 ) by draining the radiator. Flush, refill with 30% anti freeze and 70 % distilled water and sometime water wetter.
Dwight

[double ugly]

What thermostat do you use?
John

[Wayne Maybury]

Thermostat: I had a 180 in it which I thought may have been sticking since it held at one temp for a while, then later on would rise up to a higher level and stay there. When I changed the thermostat last week, I put in a 160 which runs cooler than the 180 but it also rises up to, and stays at, a higher temp after a while.

Overfilling, puking, etc: I have installed a small overflow tank which takes care of any excess coolant expansion but it had a small leak (which I fixed). Before changing the cap to a new 16 psi unit, the old cap would allow coolant to puke out on the ground even though the rad was not overfilled. After running and stopping the car 10 or 15 times, the coolant level would continue to drop down until it was well below the bottom of the rad upper tank. Changing the cap fixed that.

Temperature gauge: Yep, I have considered adding an after market gauge that will tell me what the temp really is. The original gauge in the car doesn't bounce around at all. It climbs slowly as the engine warms up and then it stays quite stable for a period of time, then after driving for a half hour or so and/or having to sit at a couple of red lights, it will creep up (I estimate 15 or 20 degrees) and stay there. It will not come back down to the original stable level that I would have observed a bit earlier. My experience with other cars is that it is quite normal for the engine to heat up somewhat when idling for a while in traffic but the temp would nomally drop back down as soon as the car starts to move at 20 or 30 MPH. This one doesn't, it just stays at the higher temp level.

I flushed the rad last night and refilled it with 50/50 coolant but I haven't had a chance to take it out for a run yet. I have also ordered a shroud which I should get by the weekend. Thanks for all the comments. I will let you all know how this works out.

Wayne

[Wayne Maybury]

Well I finally got to take the Mustang out for a run last night as I had been travelling on business then on vacation for a week and didn't have a chance to drive it until now.

Two weeks ago, I flushed out the rad and refilled it with clean 50/50 coolant then I installed the shroud. While it wasn't very hot yesterday, the engine warmed up normally and operated at a constant temperature. I shut it down for 5 minutes to allow it to heat up a little bit but it cooled right back down to a normal temp as soon as I drove it. I sat at a couple of red lights and there was no change so everything appears normal.

It looks like all is OK.

Thanks for all the suggestions.

Regards,
Wayne