14 replies to this topic

[midwestmini]

Okay,

I know there have been a number of posts on overheating problems but I think I've exhausted all my options.

History: Pump, stat and bottom hose replaced about 5yrs ago. Radiator was flushed and filled at the same time with 100% water. Coolant was replaced with 50/50 antifreeze water mix about a year ago (when I shipped the car from my old home in New Zealand to Wisconsin, USA where temps get well below freezing)

Recently I have started to get higher than normal temps (temp climbs past 3/4 under a parked idle condition in about 10 mins from a cold start). Not wanting to cook the engine (I cut the engine before RED), I have proceeded to do the following steps (testing one step at a time):

1- pulled out and replaced the 80degC stat with a same temp stat. No change.
2- pulled the radiator out and flushed it with garden hose under slight pressure both forward and backwards for 15mins. Water flow seems good. External fins have been cleaned up so the air flow path is good (they had become a little oil gummed from leaky tappet cover gasket). No change.
3- pulled out and inspected the water pump. Impellor still looks good. Note: It is the pressed steel type, not a cast impellor type, but it has worked fine for the last 4 years. No change.
4- drained out all antifreeze and run just water. No change.
5- hoses don't appear to be choking/collapsing when engine runs (heard this can happen to oil damaged hoses as the water pump draws water from the radiator).
6- there is no mayo under the tappet cover that would suggest a blown head gasket (it still continues to hold stable coolant level with no top ups required)

I have stock 1275 engine in a '79 Clubman (standard mechanical fan, no electric fan). Over the past 4 years, it has run fine sitting on normal temp. by the way: I have made no mods (timing/carb/cam) that would change performance or otherwise.

Here are my last thoughts:

a. Could a 91 octane gas with STP lead substitute cause excessive heat even under idle (Now I'm just getting paranoid that maybe I added the wrong proportion last time I filled the tank - the overheating seemed to coincide with that week, but then again....)?

b. Overheating also coincided with hot weather (90degF), but on the cooler mornings I have been getting the same results.

c. Can water from a garden hose under slight pressure, appear to flow water well through a radiator but not flush out all the cores? What method should I use to do a successful flush.

d. How much fat is built into the cooling system, ie. how hot does the outside air temp need to get in order to to force the stat to a wide open position - consider a stock radiator under a worst case load (traffic jam idle condition)? I can't imagine this is an issue - if run the car on hot days before and the needle might just hit the other side of normal.

e. I have a bypass hose installed, so I don't think I need to drill out any holes in the thermostat. Fair statement?

f. Does anyone think a incar coolant flush would benefit? What additive do I use, how much and what is the proceedure?

g. are all antifreezes created equal? What would folks recommended for an antifreeze brand or an additive for A series engines to help limit copper/iron corrosion and thus reduce crude build up?

h. I read that thermostats in the States have 'full open temp' stamped on them, whilst elsewhere in the world the 'start to open' temp is stamped on them. Not that I think it will make too much of a drastic difference can anyone confirm same?

i. the recent replacement stat I bought had a slightly smaller diameter port opening than the 5 year old stat I had in there before. From what I read, it is a standard replacement for the A-series engine - but I'd like to find out if 1- it provides any significant flow restriction for stock engine configurations and 2- do MG/Austin 1300 cars with 1275 engines have the same thermostat as a Mini even though there radiator is larger? The replacement stat is for a 1275 MG Midget (I have found that USA Autopart stores like Napa and Checker seem to track more parts for these than the Classic Mini).

Before I go a (re)replace the hoses, stat, water pump, head gasket, radiator or check timing/fuel mix or siphon a tank of good gasoline can perhaps someone shed some light for me here. The car has been parked for a month now and I'm eager to get her back on the road again.

Cheers in advance.

Graham

[cowboy]

have you treid changing your radiator cap. the pressure of the coolant system will determine how hot the engine can run aswell.

[Guess-Works.com]

91 octane Gas... That's going to cause problems for a start, especially on a 1275, use something like 95....you could be experiencing pre-ignition (pinking) which is causing the heat build up. ( or running with too much advance on the timing )

Just about all over heating problems are cured by using a plastic fan and a twin core radiator.

Also use antifreeze, most contain an agent which helps both winter and summer cooling, similar to a water wetter.

Edited by GuessWorks, 07 September 2007 - 06:40 AM.

[Gr4h4m]

had the same type of prob with mine after it had been stood for years, the rad seemed to flush well, but a new rad fixed it... the fuel doesn't sound great

[sixwheeler]

Radiator can seem to flow OK with a hose but can still be blocked. Running without antifreeze is a big mistake as it also prevents corrosion.

Also, somewhat strangely, just because the impeller on the water pump 'looks OK' doesn't mean it is. If it is covered with scale etc. it can degrade the performance of it to the point of overheating. Have replaced many a water pump that looked OK!

I'd probably start with the radiator.

Can't comment on the fuel, but you could try an octane booster to rule that out as a problem.

[midwestmini]

have you treid changing your radiator cap. the pressure of the coolant system will determine how hot the engine can run aswell.

Good thought but I know that the cap is okay. It is a long reach type (also replaced 4 years ago) and it seals well (no overflow) when I had pressure on it using the "garden hose on the radiator" trick. Additionally, when the radiator was fitted in the engine, I can hear it start to lift as the needle just hits the RED (of course at which time I cut the engine!).

[alexcrosse]

can you hear any pinking? i expect u can with that fuel

[midwestmini]

91 octane Gas... That's going to cause problems for a start, especially on a 1275, use something like 95....you could be experiencing pre-ignition (pinking) which is causing the heat build up. ( or running with too much advance on the timing )

Just about all over heating problems are cured by using a plastic fan and a twin core radiator.

Also use antifreeze, most contain an agent which helps both winter and summer cooling, similar to a water wetter.

I've been running it okay on 91 for the past year, plus there are no apparent sounds of pinging. As mentioned, the STP lead substitute I use also has an octane booster which should take it up a notch or two. My fear was that I had too much octane (which I thought might make it run hot).

Regarding the antifreeze, I only drained it out to try and raise the heat transfer out of the engine. Antifreeze solution does not conduct heat as well as 100% water. I intend to refill the system with a 50/50 mix after I have figured out what the problem is.

[midwestmini]

can you hear any pinking? i expect u can with that fuel

In the Midwest the elevation above sea level allows derating of Octane. Most cars here run on Regular (87 Octane).

[alexcrosse]

can you hear any pinking? i expect u can with that fuel

In the Midwest the elevation above sea level allows derating of Octane. Most cars here run on Regular (87 Octane).

is that a yes or no? lol.

[midwestmini]

can you hear any pinking? i expect u can with that fuel

In the Midwest the elevation above sea level allows derating of Octane. Most cars here run on Regular (87 Octane).

is that a yes or no? lol.

Ahhhh no pinging....

[midwestmini]

Tried a couple of things tonight before the wife and kids got home.

1. took out the stat and reconnected the housing.
2. tried running the engine briefly with the top hose disconnected from the radiator.
3. no flow coming out.
4. with the engine running poured a couple of cups of water back down into stat housing via the disconnected hose.
5. reconnected the top hose when warm water started to come out (good sign I thought).
6. reinstalled the stat and hoses.
7. ran the engine, still overheats!

Could I have a large airlock causing my grief?

If so, what is the best way to get the thing out.

[sixwheeler]

I re-read your original post and I have to say that if the car came to me then the first thing that I would do is change the water pump and possibly the radiator - but it is very hard to diagnose a problem from 6000 miles away!

What was the water like when you first drained it? Having been run for 5 years with no AF I would have thought it would have been rather brown? Although, as long as the car was run regularly, I wouldn't have thought the radiatior would be that blocked. If it has sitting for lond periods of time then radiator will definately rust and block-up.

If you do cure it, make sure you let us know what you did!

[midwestmini]

I re-read your original post and I have to say that if the car came to me then the first thing that I would do is change the water pump and possibly the radiator - but it is very hard to diagnose a problem from 6000 miles away!

What was the water like when you first drained it? Having been run for 5 years with no AF I would have thought it would have been rather brown? Although, as long as the car was run regularly, I wouldn't have thought the radiatior would be that blocked. If it has sitting for lond periods of time then radiator will definately rust and block-up.

If you do cure it, make sure you let us know what you did!

When I flushed and drained the radiator last year to refil with Antifreeze, the water came out very brown. It ran for 3 months with Antifreeze and then stored the car for winter (November through May) - I fear to introduce the minster to salt (on the roads for snow/ice control).

I'm going to play around with the airlock thing, after sleeping on it I have considered that maybe she is pulling an air bubble down from the heater matrix (the heat hose inlet is right next the pump suction). I'll let you know if that does the trick and if it doesn't, you'll probably hear me curse from 6000 miles away.

Well....after 20 mins of engine running and lots of hose squeezeing to try and burp out air....no change. The hoses are only a little warm. The top hose seems to build up pressure - sometimes. The hose closest to the bulkhead is hard to squeeze (hot exhaust on one side, fan running on other side !!!!). During all this time the gauge sits just under the red. This doesn't make any sense to me. Maybe I'll try draining the whole system down and refilling it slowly again with the heater hose disconnected. I can't believe how many other posts seem to have this exact same problem and no one has provided a good summary of what they did to troubleshoot it. Being of Scottish background, I'm refusing to fork out to buy new parts if the old ones appear to 'look' okay.

More to come....

Edited by midwestmini, 11 September 2007 - 03:40 AM.

[midwestmini]

As promised .... but way overdue, I fixed the problem tonight (note ..... this reply is also posted to my other forum topic on Smiths temperature sensors.)

For what its worth, don't monkey around with old temperature sensors.

Even though you think they may read right - always buy a new sensor if you remotely think that your old sensor is bad.

I convinced myself my old one way okay by testing it on the stovetop with an ohm meter and was at the point of replacing water pump, radiator etc. before I decided on a whim to just try and replace it with a new sensor (Unipart #GTR101 or from Napa the equivalent is #ATM1434031).

I went from a state of paranoia believing the engine was overheating (gauge just hitting the red) to seeing the gauge back down in the normal (1/3 to 1/2 temp range) after a new sensor was installed.

Back on the road again....ahhhhhhhhhhh.