Took midget for a spin yesterday.

[regularman]

No fuel problems at all and I adjusted the timing and got it all where it feels good but after about an hour and a half, the temp went up to hot when I was climbing a large hill and it overheated. I let it cool and put water back in it and it drove on after that just fine. I put my pressure set back on the system and it held 15 psi just fine for a while,so I must have a restriction of water flow or something.

 

[regularman]

Also, can someone explain exactly how that can with the radiator cap on it is supposed to work? Every time I check the water is low in the radiator but is full in that can/bottle.

 

[jlaird]

As water heats it expands into bottle, as it cools in radiator it contracts and is pulled back in.

Radiator to bottle should be closed system but bottle should be vented.

 

[BugEyeBear]

Hi Kim,

I'm guessing that the rad is pushing coolant into the overflow as it gets hot & expands, BUT it isn't sucking fluid back in as it cools.

I'd look at the overflow bottle & ensure that the "suck" tube goes all the way to the bottom. If it ends at the top (or is damaged near the top) it won't suck back in when coolant cools down and volume contracts.

Otherwise look for leaks in the hose between the bottle & rad, or perhaps a faulty cap on the rad that allows air to be sucked back in??

I kinda suspect the cap is faulty.
Cap might have not been holding pressure, thus partially causing your overheat?
(This wouldn't show up during your pressure test because you removed the cap during the test. Did you test/inspect the cap?)

Good Luck, I hope you figure it out!!

"Cheers!"
-Bear-

 

[regularman]

Here is what I don't get. I can shut the car off and let it cool over night and check the water in the radiator and there is air pressure in there. Its like it gets hot and boils and then cools down but the pressure never quite goes away.

 

[DrEntropy]

Cap. Get a new one.

 

[regularman]

I pressure checked my existing one and it seemed to hold fine but caps are cheap enough. I just can't figure this thing out. After a long time it heats up and boils and leaves an air pocket in the top of the radiator and the bigger the pocket the less cooling and the more boiling.

 

[BugEyeBear]

Is it pressure that's still in there... or VACUUM (i.e. suction)?

Sounds like either your cap isn't permitting suction, OR there is some sort of defect in your vent/suction line...

Seems like it lets pressure out, but doesn't suck coolant back in.

I'd get a new rad cap (as you said, they're CHEAP), & I'd take a good look at the vent/suction line to ensure that it has good flow in both directions.

I'd test it by putting clear water in the overflow tank and try sucking on the hose. (Don't swallow any though as there is bound to still be some coolant or crud in there!) Better test would use some sort of vacuum pump poked into the rad end of the hose from within the rad cap flange (keeping the vent/suck hose attached to the rad). Also a good idea to check that crud isn't floating in the bottom of your overflow tank and clogging the pickup when it trys to suck coolant back in.

-Bear-

 

[aeronca65t]

If your car runs OK most of the time, but overheats under certain conditions, it could be a collapsing lower radiator hose (sucking closed).
Squeeze the lower hose and see if it feels soft (some have a spring inside them to prevent collapsing).
Even with a good cap, this can cause the car can overheat and eject water. Water will go into the little tank but even that will allow water to escape at some point.
You seem to have something causing overheating....bad lower hose, clogged rad, stuck thermostat, slipping fan belt, "backwards" fan blades (it happens!), etc.

 

[regularman]

Electric fan. Had to take a package to drop off at a fedex/kinkos and the only place still open was downtown. I took off in the midget and hotrodded it around town and the fan came on and brought the temp back down and it ran just fine and I ran the heck out of it passing about everything on the road and it never overheated. Of course its in the 70s here today though, I also took it back up on the parkway and it started to heat up again. I was doing the same rpms in town and no overheat but something about climbing those steep hills from 2500 feet to 6000 feet in about 15 miles just makes it heat up when I really make it pull. Was in the 60s up there so its not the outside air temp.

 

[texas_bugeye]

I kind of remember some issue with water pumps a + year or so ago. something about them rubbing on the block and the vanes diameter. Just a thought I'll try and find the info on it.

 

[texas_bugeye]

Got it the water pump for a 67 12CC block needs the shorter pump. If your using that pump on other than eng as it would fit just less pump it could be it cant circ enough under heavy load.

 

[regularman]

I have a 12CD block from a 69 (I believe)and I don't know which pump I have. It was put on new during the rebuild but I don't know if the vanes are short or long. Anyone got some pics of either so I can tell the diff if I pull mine off ?

 

[BugEyeBear]

Hey Kim,

My Ex-wife's Toyota Tercel (aka "Turd-Cell") used to get really hot when climbing long hills (we lived in SanDiego back then & it used to get hot on the road to LasVegas, there is one really long climb approx midway). I would turn off the A/C to reduce engine load, drop the trans from 5th to 4th, & put on the heater full-blast to act as a supplemental radiator, & all this would keep the engine from overheating. (This was BRUTAL in the middle of summer, & we'd be sweatin' like stink by the time we reached the crest of the hill.) As soon as we crested the engine temp began to drop, & we quickly turned on the A/C again.... :eeek:

All the rest of the time that car ran in the normal temp range. Only got hot on these sort of heavy load extended hill climbs.

ANYWAY, long-story-short (too late?) I later discovered that the car had a faulty thermostat that wasn't quite opening all the way. This was acting to limit water flow & didn't allow for enuf cooling at peak conditions. I changed the thermostat & it never overheated again.


Not sure if this would be your prob, but I thought it was worth mentioning...

I still suspect your cap is faulty, but might be a few small items that are adding up to cause your overheating problems.


TOO BAD your Midget has a temp guage instead of just an idiot light. If you just had an idiot light the problem could be easily fixed by just removing the bulb. :crazy:

"Cheers!"
-Bear-

 

[Gray_Cat]

This is a way out from left field post but just wanted to throw it out there. Have you checked your dizzy lately? That is, the interior physical condition. A long time ago (yep in a galaxy far far away) I was driving from Arkansas to California after a 3 year stint in the Army (1 year in Nam) in my 62 Chevy Nova II. It was August so was scalding hot all the way. The car kept overheating (had no AC) and I tried every remedy I could including a complete removal and boil out of the radiator. Still overheated but I managed to get to Cali and one of my older brothers (a mechanic) looked at it. He immediately found the problem - the dizzy was almost completely packed with metal shavings. The engine didn't miss or anything but the timing was either advancing or retrading all the time causing the whole system to stress and resulted in overheating. We went to a wrecking yard, got a good used dizzy, put it in and never had an overheating problem again. I guess I saying, check all engine systems as the overheating may not be a cooling system issue.

 

[JPSmit]

OK, here's another from left field. I am currently reading a book on the history of MGB's. They were talking about developing the B series engine and that they initially had overheating problems. One of the MGB developers recommended using less oil as the crank was churning the oil which apparently heated it up. They lowered the oil level and the problem went away. If this happens only when the car is on an angle, could this be a factor?

 

[regularman]

I think I am going to just keep the water topped up before each time I go out and drive the dang thing, unless I figure something else out. New radiator, electric fan, thermostat, extra heater core installed at the rear for more cooling. It runs too good for it to be a too lean condition or the timing to far out. There has to be something else. I could not find a real blockage of any kind in the head when I ran water through it. Maybe it is a lack of circulation from the pump. Its funny how it settles out at one place, which I assume is the 160 degree mark for the new t-stat and then after some hard running it takes off higher and then the hotter it gets, the hotter it gets, I assume because once getting hot it loses water and then with less water comes even less cooling.

 

[tony barnhill]

Let's backup a step before we continue putting bandaids on the system:

1) When did you last replace both radiator hoses?
2) What rating is your car?
3) When did you last <span style="font-weight: bold">BACKFLUSH</span> the engine block?
4) Is water flowing through the heater core (the real one) & back into the radiator?
5) How old is the water pump? Is it OE or aftermarket?

Disconnect that extra rear heater core & see what happens.....

Also, how is that electric fan attached to the car (not through the new radiator, I hope)? Is it a pusher in front of the radiator or a puller in the rear? & is it turning properly?

 

[startech47]

If you have an expansion tank connected directly to the radiator and the pressure cap is on the expansion tank, than you also need an overflow tank.

 

[tony barnhill]

If you have an expansion tank connected directly to the radiator and the pressure cap is on the expansion tank, than you also need an overflow tank.

Wouldn't an overflow tank on a closed system 'open' the system? RB MGB's with expansion tanks don't have overflow tanks - an expansion tank is an overflow tank.