Overheating at cruise
- Thread starter Bort62
- Start date
Also check your vacuum advance, esp if you are still using a Loadomatic. No advance due to a bad diaphragm will cause overheating at cruise.
Other possible causes for cruise overheat are:
- clogged radiator (insufficient coolant flow)
- bad water pump (insufficient coolant flow)
- bad lower hose (sucked shut causing low coolant flow)
- bad head gasket (combustion gasses in coolant)[/code]
Other possible causes for cruise overheat are:
- clogged radiator (insufficient coolant flow)
- bad water pump (insufficient coolant flow)
- bad lower hose (sucked shut causing low coolant flow)
- bad head gasket (combustion gasses in coolant)[/code]
A
Anonymous
Guest
MustangSix":2mpvfcxs said:
thats what started my problems. think about it...a 35+ year old radiator....yuck
Well, it's a new radiator so I don't think thats the problem. New hoses too so I doub't it is collapsig but I will check.
The water pump is of unknown quality, so I have a replacement here to put on.
The timing is a good point, but I have a duraspark GM module combo so i don't think It's that. Im not sure that my timing is set perfectly but It is at least pretty close.
Runs well enough.
The water pump is of unknown quality, so I have a replacement here to put on.
The timing is a good point, but I have a duraspark GM module combo so i don't think It's that. Im not sure that my timing is set perfectly but It is at least pretty close.
Runs well enough.
Aerodynamic Stagnation?
Interesting. I had no real problems with the car before but its got a new engine/trans combo so who knows.
New water pump in but I havent taken it out to test yet. The old pump looked fine however so im not too hopeful.
Could be the head gasket I guess, I have had problems there and I noticed a crack in the head on the pass side front head bolt.
Interesting. I had no real problems with the car before but its got a new engine/trans combo so who knows.
New water pump in but I havent taken it out to test yet. The old pump looked fine however so im not too hopeful.
Could be the head gasket I guess, I have had problems there and I noticed a crack in the head on the pass side front head bolt.
66 Fastback
Famous Member
No pressure in the cooling system?
Bad radiator cap? That might explain overheating at highway speeds when the engine's heat rejection is greater/hotter. Without a functioning radiator cap, the boiling point would be lower. At idle, the engine's heat rejection is lower, so you might get by with a lower system pressure at idle assuming the other cooling system components (radiator & pump) are up to snuff.
As Jack mentioned, I would suspect insufficient ignition advance at cruising speed. Check the vacuum diaphram and the centrifugal advance mechanism on the distributor to make sure they are working.
Doug
Sorry, I mis-spoke.
The rad holds pressure fine - what I meant is that after starting it up cold for a minute and shutting it off, there is no pressure in the cooling system so I don't think there is a leak between the cooling jacket and the combustion chamber. (nor any evidence of steam in the exhaust)
Ignition advance sounds like the likely culprit. I have a DSII that I recurved as per the sticky on the top of this forum. As far as I can tell, it seems to run fine. I doubt that diapragm is busted as it is a newly remanufactured distributor but I guess it is possible. I will have to put the timing light on and see if I am getting vac advance.
I know the centrifugal advance moves freely, but I haven't tried putting a light on it and and seeing if it goes up with RPM.
It seems like it should run a lot worse if it wasnt getting any advance but I don't know. Worth a shot.
I don't think there are any air pockets trapped in the system as i've done a pretty good job flushing it out. I've done this a few times before
And the heater isn't hooked up, so I can't use that as a diagnostic. Coolant is getting hot however.
The most frustrating thing is, its not even hot here. I overheated in on the freeway when it was below freezing outside. Leads me to beleive something is fundamentally wrong that I just haven't noticed yet.
The rad holds pressure fine - what I meant is that after starting it up cold for a minute and shutting it off, there is no pressure in the cooling system so I don't think there is a leak between the cooling jacket and the combustion chamber. (nor any evidence of steam in the exhaust)
Ignition advance sounds like the likely culprit. I have a DSII that I recurved as per the sticky on the top of this forum. As far as I can tell, it seems to run fine. I doubt that diapragm is busted as it is a newly remanufactured distributor but I guess it is possible. I will have to put the timing light on and see if I am getting vac advance.
I know the centrifugal advance moves freely, but I haven't tried putting a light on it and and seeing if it goes up with RPM.
It seems like it should run a lot worse if it wasnt getting any advance but I don't know. Worth a shot.
I don't think there are any air pockets trapped in the system as i've done a pretty good job flushing it out. I've done this a few times before
And the heater isn't hooked up, so I can't use that as a diagnostic. Coolant is getting hot however.
The most frustrating thing is, its not even hot here. I overheated in on the freeway when it was below freezing outside. Leads me to beleive something is fundamentally wrong that I just haven't noticed yet.
Oh yeah, electric pusher fan that seems to work just fine. It will sit and idle all day without a problem (fan on). I haven't had any problems around town either. It's only when I get out on the freeway after a few miles (5-10) it starts to peg the gauge and boil over. If keep my speed down around 55 it stays right below boil over but any faster and it goes.
I have a manual switch for the fan and i've tried cruising with it on and off and there is no real apparant change.
I have a manual switch for the fan and i've tried cruising with it on and off and there is no real apparant change.
Mercury Mike
Famous Member
Sounds like a pressure-related issue in the cooling system. Same thing happened in my '97 Pontiac awhile ago. I put a new cap on the radiator, bled the cooling system (It has a bleed valve on the top of the system in that car, though), flushed, replaced thermostat and coolant/water, haven't had a problem since!!! =)
It could also be leaning out, but I have seen/heard of so many early Falcons that just seem to develop a stagnant zone around the front grille at the kind of speed mentioned. Try driving with the bonnet catch off and the front safety wired to provide 2" clearance.
No heater? Freezing temps? That must be kinda a bummer!
Is the heater core still plumbed into the system? If so is it right and clear flowing? If no core how did you do the bypass or are the ports just capped?
Is the heater core still plumbed into the system? If so is it right and clear flowing? If no core how did you do the bypass or are the ports just capped?
Some other thoughts.
1.) Are you CERTAIN the thermostat is in and facing the RIGHT direction? No thermo lets the water circulate too fast when the engine is reved. A reversed thermostat will be forced shut at highway engine speed.
2.) Did you drill an 1/8 inch hole in the thermostat flange? This acts as an air bleed to let the block and head fill with coolant. The thermostat flange has a rippled around the primeter for added sealing. Drill your hole just nside of that. Install the thermostat will the new hole up, so as the block fills, the air can escape. My other method of "burping the baby" was to leave the heater hose that comes out of the head off (but pointed up) until the cooling system was filled. drilling the hole is much less messy and permanent.
3.) Check your lower radiator hose by reving the warm to hot engine to 3000 in the driveway while watching the hose. If there's ANY movement, the hose nees a coil spring inside of it to stop it from collapsing. Original equipment had the spring.
Good Luck
1.) Are you CERTAIN the thermostat is in and facing the RIGHT direction? No thermo lets the water circulate too fast when the engine is reved. A reversed thermostat will be forced shut at highway engine speed.
2.) Did you drill an 1/8 inch hole in the thermostat flange? This acts as an air bleed to let the block and head fill with coolant. The thermostat flange has a rippled around the primeter for added sealing. Drill your hole just nside of that. Install the thermostat will the new hole up, so as the block fills, the air can escape. My other method of "burping the baby" was to leave the heater hose that comes out of the head off (but pointed up) until the cooling system was filled. drilling the hole is much less messy and permanent.
3.) Check your lower radiator hose by reving the warm to hot engine to 3000 in the driveway while watching the hose. If there's ANY movement, the hose nees a coil spring inside of it to stop it from collapsing. Original equipment had the spring.
Good Luck
Well I am going to start a huge arguement here, but I can pretty much prove conclusively that having no thermostat in does not cause any problems with overheating.
I am a thermal engineer, and I spend most of my days designing and analyzing systems to cool things off. People will argue with me about this but it is one of the subtle corners of engineering that most people just do not understand. It may appear to make that car run hotter, but that is a false observation. If anyone really wants to know I can tell you but it's really too much for general discussion (I have discovered that the hard way).
So, that being said - I will check the lower radiator hose as that seems possible. I haven't driven much these last few days but Ill try to sneak out from work today and give it a try.
And in case you didnt guess, I don't have a thermostat installed.
I am a thermal engineer, and I spend most of my days designing and analyzing systems to cool things off. People will argue with me about this but it is one of the subtle corners of engineering that most people just do not understand. It may appear to make that car run hotter, but that is a false observation. If anyone really wants to know I can tell you but it's really too much for general discussion (I have discovered that the hard way).
So, that being said - I will check the lower radiator hose as that seems possible. I haven't driven much these last few days but Ill try to sneak out from work today and give it a try.
And in case you didnt guess, I don't have a thermostat installed.
Maybe we should have this thermostat discussion over in the hardcore tech area if you are going to get very technical but I would like to hear your reasoning. I have read that some engines will run hotter because the coolant will spend less time in the radiator releasing heat than is optimal. In practice however, I have found some engines to run cooler without a thermostat and some run hotter, some had no change. And yes they all took much longer to warm up without the thermostat, so they were predictably consistent in that way.
Typically an overheating problem "at speed" means that the radiator is not allowing the heat to tranfer. Its either partailly plugged or too small. The old rule of thumb is that after 30-35 mph the engine does not need the fan, the air speed is greater than what the fan can pull.
Sounds like you installed a new engine
, is it larger than what it replaced? I have an overheat problem too (well it runs hotter 
, but luckily does not boil over) with my new engine. But it has the 250 head with a larger cam shaft. I'm assuming that the engine is just pumping more air and fuel (read: generate more BTUs) and the stock radiator can't keep up.
Also, just because the rad is new does not mean that it is OK
. You could take it off and have it flow tested. I would do that before the next step: installing a rad with more cores or fins/heat transfer area.
Personally I think you should try intalling a t-stat and try that. Make sure you put the bleed hole in it. I used a center punch to poke a hole in mine; faster than getting my drill and bits out. Anyway, the t-stat might slow the water flow rate down enough get the heat out of it in the radiator Plus it the cheapest "fix" for right now!!
Sounds like you installed a new engine
, is it larger than what it replaced? I have an overheat problem too (well it runs hotter , but luckily does not boil over) with my new engine. But it has the 250 head with a larger cam shaft. I'm assuming that the engine is just pumping more air and fuel (read: generate more BTUs) and the stock radiator can't keep up.Also, just because the rad is new does not mean that it is OK
. You could take it off and have it flow tested. I would do that before the next step: installing a rad with more cores or fins/heat transfer area.Personally I think you should try intalling a t-stat and try that. Make sure you put the bleed hole in it. I used a center punch to poke a hole in mine; faster than getting my drill and bits out. Anyway, the t-stat might slow the water flow rate down enough get the heat out of it in the radiator Plus it the cheapest "fix" for right now!!
Bort62":2irgaemy said:
Hmm...not sure what exactly you mean to say technically, but I can tell you that eliminating the thermostat on a 351C will definitely cause overheat problems, but for different reasons than you might think. It's true for some other engines and might even hold for a 200.
What happens on the cleveland is that the t-stat causes flow restriction that increases pressure inside the block, reducing the formation of small boiling points and increasing the heat transfer. The overall system pressure is still limited by the radiator cap. The effect is that you have a system that acts like it is operating under higher pressure, but is still only running at 12-14 psi at the radiator. You can remove the t-stat, but it has to be replaced with a restrictor to maintain the internal pressure.
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