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MG Midget and Sprite Technical - 1500 Cooling - Well, I THOUGHT I'd fixed it.

Hi, all.

You may recall that back in the summer I experienced some high temp indications while driving to "50 Years of Spridgets" and back. After returning, I had a look and found that my radiator cap was faulty. So I replaced the cap, and thought that all was well.

This past Sunday, I had the car out for a relatively short drive of 12 miles on the interstate, sustaining a speed of around 65mph. And once again, the temp climbed way up toward the red. Gaahhh... I couldn't blame the weather this time, since it was a very pleasant and mild day.

Once I got back into town, the gauge dropped to the normal range.

So what do you all think? I've heard of engines heating up while puttering about in town with reduced airflow through the radiator, but in my case it's the opposite - the overheating only occurs at speed. Is my water pump losing it? Maybe a bad thermostat? Silted radiator? (By the way, I had the rad recored only a few years ago, and have always used a 50/50 coolant and water mix, so I'd be surprised if it's blocking up.)

Opinions welcome!

-:G:-
Gryf Ketcherside

Gryf,

I know its a differnt kettle of fish so to speak, but had a similar problem with the land rover not too long ago.

Each thing I tried helped a little.

Got a new rad with larger cores, changed the cap, flushed the system, changed a couple of hoses, water pump etc.

It was a bit of an elimination process, however I also found that the rear shoes were binding slighty, not enough no notice in normal conditions, but pushing uphill on a longer run the engine was obviously working harder to maintain speed. Not suggesting for a moment that this is the issue, but wanted to share never the less.

Are any of the wheels getting hotter than usual to the touch after a run?

I understand that the obvious is not always the case, and a supplementary question if you like, does anyone know if these symptoms can be caused by a tuning issues (long shot perhaps)?
Jim Stewart

Sorry forgot to add,

I never usually run on a 50/50 mix, usually less 30/70, I don't know if antifreeze has as good cooloing properties as water (another long shot)
Jim Stewart


Did you have the heater on?

Might be a slow to open thermostat and the heater is doing the cooling at low engine speeds, when you use more power, you need more cooling, but the thermostat doesn't respond, so the temp climbs!

Andy
a borris

Gryf, as I remember your car is still original with all the emmisions controls in place. Can't remember for sure, but I think the distributor on that model is a vacuum retard unit. I found out in my car when I had the timing off that running at highway speeds with retarded timeing would cause it to overheat. Try blocking the vacuum line to the dizzy and do another drive and see what happens. You may want to readjust your timeing or alter the amount of retard.
Bill Young

Fan clutch?
Richard 1979 1500

I have a gut feeling its a rash of bad thermostates that are now being made in china

I to have suffered on my truck from over heating...but only on 1st start up in the morning...then ran fine the rest of the day, my guess is the wax snint has been altered and is taking longer to warm up then the rest of the engine and cooling systm...its seems to be an epidimic as to how many people are having overheating problems latly

What I ended up doing is removing the giggle pin and driling the hole a bit larger then an 1/8th inch...(Ididnt have an 1/8th inch bit)...no problem scence...

I dont know if that helps

Im guessing you checked the belt for slippage on the water pump

does your 1500 have a clutch fan on the fan blades sect. Maybe it has gone out or going out...I had that happen before and will create overheating at speed...but at long idle as well.

let me know if you need anything/help gryf,

prop
Prop

hey richard,

clutch fan or fan clutch....at least we are thinking the samething

prop
Prop

>>> Gryf, as I remember your car is still original with all the emmisions controls in place. <<<

Well, it's not completely original. I'm running a Mallory distributor with a pertronix in it, and the advance/retard is all mechanical.

And besides, this is a fairly recent development. I've had no cooling problems for several years, until it started to crop up over the summer. So I may start cheap, and stick a new thermostat in there.

>>> Fan clutch? <<<

Good guess, but I'd think that a bad fan clutch would cause problems at lower speeds, when you need the fan the most. Out on the highway you have your speed forcing air through the rad, and that's where I'm seeing the heating.

>>> Did you have the heater on? <<<

Nope. It's not that chilly here yet! ;-)

For that matter, it may be something silly like the temp sensor. I had to replace that some years back, and the symptom was that it registered hotter and hotter, until it would snap to full hot when starting in the morning from cold.

Thanks for the comments - I'll let you know what it turns out to be.

-:G:-
Gryf Ketcherside

All good advice.

My 50p is on thermostat not opening fully... so the block's hot but the rad's relatively cool since there's not much flow...

A
Anthony Cutler

The way I see it, the problem is observed when cruising at higher revs. There are several potential explanations.

1. The cooling system is less than adequate for the car, leading to "heat soak" where the heat is being generated faster than the system can dissipate it. This could be because of increased horsepower, clogged radiator, bad thermostat, tired water ;-), or too many badge bars. As noted above, crank up the heater to get home.
2. Lean air-fuel mixture, especially at higher revs.
3. Retarded timing.

Has the radiator been flushed? How old is the thermostat? Is it still the original water pump? Do these units have impeller issues like some of the A-Series units do?

Is it possible that your carb is set a bit on the lean side. You know more about your Zenith than I ever will, so I will leave it at that.

Did you set up the Mallory yourself? How did you decide on the advance curve? How did you decide on the amount of advance at idle? Have you used a timing light to see how much advance you are actually getting at the rpm you were running on the highway? Cruising on the highway is where a normal vacuum advance would be active, thus we can say that your advance is probably retarded from the ideal, since you are running mechanical only. Yes, I do understand that this car came with vacuum retard, but that is an issue with the vacuum source matched to the distributor's vacuum module. It still comes down to more advance when cruising and less when accelerating; even BL could not affect the laws of physics that much. The vacuum retard was yet another way of trying to minimize emissions at idle. Therefore, it should NOT be assumed that the advance quoted in the book as correct for the Lucas distributor at idle would be correct for the Mallory distributor at idle. Check with Mallory. It might be easier to lurk on some Spitfire forums or ask a Spitfire dealer for info on the correct curve and settings for the Mallory in a 1500 engine.

David "full of questions" Lieb
David Lieb

I had a similar problem with my '78.
It turned out to be the head gasket. At higher speeds some of the combustion gases were escaping into the coolant jacket causing overheating. A pressure test of the coolant system did not reveal it, but there was a test that showed combustion gases in the coolant.

At lower speeds no problems, at highway speeds, it overheated.

Mike
Michael Hirsch

>>> I had a similar problem with my '78. It turned out to be the head gasket. At higher speeds some of the combustion gases were escaping into the coolant jacket causing overheating. <<<

Ouch. I'll keep that in mind if the easier fixes don't catch it first.

As for the advance curve, etc., I've run the all-mechanical Mallory for several years now, and cooling was never an issue until very recently. So unless something changed in there, I wouldn't suspect it. But again, I'll keep this in mind! I do keep the advance weight mechanism lubricated, by the way. FYI, I bought this distributor from Bob Gardner, who had used it in his 1500 race car before going to a different ignition system. It's worked great - performance is fine.

In answer to another question, I've checked my advance using my dial-back timing light, and while everything looked fine, I don't remember the actual numbers involved.

I haven't flushed the radiator, although that's on my to-do list. Again, I had it recored not all THAT long ago. Dumb question - does the coolant flow from the bottom to the top of the rad, or vice-versa? I want to make sure I'm actually back-flushing it. (Sheesh, I should know that...)

As for running lean at speed, I haven't had to adjust my mixture for a long time. And when ZS carbs get out of whack, they usually tend to go rich. Besides, if my car was running lean, you'd think it would get better mileage on the highway than the 30 or so I'm seeing. (Keeping in mind the smaller US gallon.)

-:G:-
Gryf Ketcherside

Unless your losing antifrezze I cant see the head gasket being a real issue....

How old is the water pump...maybe its seen its better day

if all else fails, do what I did and drill an 1/8th inch hole in the stat...it seams to work fine for me...No more over-heating of the truck, and runs a good temp where its supposed to be.

prop
Prop

Gryf,
The water comes out through the thermostat to the radiator. Everything else can be figured out from there.
David "trying to keep it simple" Lieb
David Lieb

Gryf,

It may very well be the head gasket. Not a big deal to change, but I'd try a few other things first.

Remove the thermostat completely and go for a drive. In fact, come join us Sunday morning for the the annual wine tour with the Triumph Club. Those guys can know our engines better than the MG kids.
http://stlouismgclub.com</Events.aspx?Date=8caff94c38cc000>

Also check the fan clutch. Wiggle the fan blade (engine stopped) and see if has more than a little play. If you need a newer one let me know.

If it still runs fine even when the gauge is pegged, I would suspect a faulty indicator. Buy one of those infrared thermometers from Harbor Freight for $10 a see just how hot things are.

See you Sunday.

Lee
L Fox

If it is happening at highway speed and not at low speed, it isn't likely to be the fan.

Prop,
If the HGF is pressurizing the coolant, you won't necessarily see coolant loss. Makes it a bugger to diagnose. The device that sniffs the coolant for combustion gases is about the only test for it.

I don't think I would eliminate the thermostat completely, but I would look for an old one and gut the mechanism out of the center and install the disk.

If the temperature gauge is indicating normal temps at low speed, you should be able to watch the needle carefully and see the thermostat opening and closing. If so, the gauge is probably right or near enough for government work.
David "heating things up" Lieb
David Lieb

I know what you mean about the HG failing without leaking fluid....but that is so rare IMHO. to be honest,,,I dont understand the concept of how that happens...is it the vary beginning of a HGF...maybe a gasket seperation of some type....the good thing about cooling systems are theres not much to figure out whats wrong...Take my truck for example, it only took 3 years for me to figure out how to keep it from over heating...in geology time (rocks, mountians, and canyons) that like an atomic nutron flash...LOL.

prop
Prop

Gryf, stick a meat thermometer in the thermostat housing an compare the reading against the C-N-H of the gauge. It will at least give you some indication as to how accurate the gauge is.

Anitfreeze boils at a higher temperature than water does even under pressure. That is just in case you want to adjust your af to water ratio in the future.
Clive Reddin

"when ZS carbs get out of whack, they usually tend to go rich"

Overheating Catalytic converter?
Richard 79 1500

Gryf:

If you have one of those mechanic's stethoscope tools, listen to the water pump near the bearing, anywhere on the housing really. A good pump will make a smooth "woosh-woosh-woosh" sound. Can't remember the sound of a bad WP, sorry.

To check for a functioning thermostat, start the car cold, open the hood, and hold the big hose above the alternator in your hand and wait. you will recognize the moment the thermostat opens, the hose temperature changes dramatically and rapidly, you can't miss it.

FWIW, This has no relevance to your current problem, but my car used to run hot all the time, between 12:30-1:00 on the gauge, to pushing against the orange upper limit regularly. With the modifications* it rarely reaches the hashmarks at straight-up 12:00 anymore, more in the 11:00-11:30 range, and VERY sensitive to the outdoor air temperature.

*Downdraft Weber, header (no cat), oil cooler, advance distributor, 16 btdc timing, no air pump, egr, or gulp valve.
Richard 79 1500

>>> Overheating Catalytic converter? <<<

Thanks, but I can rule that out. After torching the "cat" several years ago thanks to a Grose Jet float valve that allowed copious flooding, I finally punched the innards out of the converter, so it's now just a fat downpipe.

>>> If it is happening at highway speed and not at low speed, it isn't likely to be the fan. <<<

My thought exactly. And besides, the fan clutch (in response to some other comments) is running smoothly, with no wobble at all. So I think it's still fine.

>>> The water comes out through the thermostat to the radiator. Everything else can be figured out from there. <<<

Thanks! Makes perfect sense when you think about it. My biorhythms must have been low when I asked that...

>>> Unless your losing antifrezze I cant see the head gasket being a real issue.... How old is the water pump...maybe its seen its better day <<<

I'm not seeing any coolant loss, and the stuff is still clear and green. The level stays around the halfway point in the expansion tank, as it should. And I agree about the water pump. As far as I know, it's the original.

Having said all that, I think I'll try replacing the thermostat first, and if that's not the problem, I'll backflush the radiator. And I'll put the water pump high on my list of suspects.

Thanks all,

-:G:-
Gryf Ketcherside

>>>>My biorhythms must have been low when I asked that<<<<

Have you looked outside of your window the last several nights, there is a large bright white ball in the sky...only comes around twice a year...harvast and planting season

prop
Prop

My 1500 temperature is a slight bit higher at extended highway speeds and drops when I leave the highway. It never leaves the normal range and is well within the safe range. Are the higher temps somewhat normal at higher rmps.
RJS Scottaline

>>> My 1500 temperature is a slight bit higher at extended highway speeds and drops when I leave the highway. It never leaves the normal range and is well within the safe range. Are the higher temps somewhat normal at higher rmps. <<<

Bingo - the temp climbs up near the red line at highway speeds, and then drop back toward normal when driving around town.

-:G:-
Gryf Ketcherside

Could it be that the water pump is too efficient? At higher engine/road speeds it is pumping the coolant through the radiator so fast that it doesn't have time to cool off properly.
Martin

The 76 indicator is a bit different, but it never goes past the half mark. I think the rise in temps in moderation might be normal.
RJS Scottaline

>>> Could it be that the water pump is too efficient? At higher engine/road speeds it is pumping the coolant through the radiator so fast that it doesn't have time to cool off properly. <<<

As I understand it, the thermostat tends to modulate the coolant flow by providing just enough of a restriction to give the proper flow rate.

>>> The 76 indicator is a bit different, but it never goes past the half mark. I think the rise in temps in moderation might be normal. <<<

Well, mine used to stay around the halfway mark all the time, so the recent hot indications really are abnormal.

Gryf "Abby Normal" Ketcherside
Gryf Ketcherside

Gryf,
If you have not yet cured your overheat problem at highway speed, I would most certainly look at the fan clutch. With the engine off, reach in a spin the fan blade. If it spins freely, the clutch is bad. Give me a call and we can talk about it.

John
mgdoc

Hi, John!

Thanks for checking in. Would a bad fan clutch really cause heating at highway speeds? I always figured something like that would be apparent mostly at low speed, when the fan is needed most.

My fan clutch turns smoothly, with slight resistance, as it has for years now. As far as I can tell, nothing's changed with the clutch.

-:G:-
Gryf Ketcherside

Gryf,I kmow this sounds unlikely,but have you checked the tappet gaps lately? I had a similar problem to you a few years ago and tried everything,new rad,thermostat(and removing stat),fitted additional electric fan,larger engine fan etc!All to no avail.Eventually ,after servicing the car whicw included adjusting the tappet clearances-fault cured!They weren't very tight,maybe 7 or 8 thou when they should be 12 thou,but was obviously enough to make the engine struggle to fire the mixture. No problems since including a run to Monza over the Alps!Hope this is of help,Regards Steve
Steve Smith

Steve -

Interesting suggestion! I think my valves are set about right, but it's been a while since I've had the rocker cover off. So If I get some time, I may check them just for peace of mind, if nothing else. Besides, I've had a spare rocker cover gasket hanging out in the garage for years, and I may as well give it something to do.

;-)

-:G:-
Gryf Ketcherside

Gryf, it may be worth checking your plug colour after a run at 65mph - would show if you have a lean mixture issue at speed and under load - I am thinking air leaks at the manifold?

I guess from the thread you aren't loosing any coolant - obviously a pressure leak will cause an overheat as you rad. cap. did..


The only other suggestion which I think someone else already made was to try runing without the 'stat entirely, the temp will take longer to rise - but should in theory end at a similar level - if this solves the issue it may indicate you aren't getting enough flow with the 'stat in place.

This could mean pump is performing poor or that you have a restriction in the your coolant flow somewhere - furring or corrosion etc..

If the engine has done many miles or been siting a long while corosion/sediment might have reduced the cooling passage sizes and thermal conductivity ?

I don't know if you can check the fan clutch by reving stationary ?

Good luck with your next run

PS
my 1500 has been laid up in the garage for 15 years - part welded up - rhs sill, and rear wind to be finalised before its bodily fit.. Engine hasn't run for this long either - I suspect your problems will be nothing as to what I will find....




John Barber

I put in a new thermostat yesterday, but haven't yet had a chance to go for a test run. Busy weekend, and migraines to boot. Argh.

But I'll report in when I get a chance to test.

Thanks again for all the suggestions!

-:G:-
Gryf Ketcherside

One point here. If you do wish to read the plug colour, you MUST cut the engine while it is under the conditions in question and check them immediately. If you go out for a drive and wait until you get home to read the plugs, you are wasting your time because the plugs will reflect what has been happening most recently. Unless, of course, you are running so lean that chunks of porcelain are falling off, etc. Not the case with Gryf, I am sure, as he would surely have mentioned a detail like that ;-)
David "pedant at large" Lieb
David Lieb

Hey david,

In that situation would it be a good idea to "Break" the spark plug seal to head Before you go on the drive, while the engine is cold.

yeah I learned the true value of anti-seizure compound at 19, while changing plugs at a friends house on a sunday night...with the engine hot...


Prop....I didnt know spark plug threads are removeable...Prop
Prop

This thread was discussed between 14/10/2008 and 20/10/2008

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