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Forum Index : Other Stuff : MINI ENGINE: How hot is too hot?
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Classic A-series 1275cc engine and box. Not in a Mini, but a Morris 1300, but it is the same engine/box arrangement. I think my temperature gauge is lying to me.  With normal town driving, the gauge sits just above the normal mark, but when you get out on the motorway and push her, the gauge goes pretty much all the way over to the HOT mark on the right. Concerned about this, I decided to do some tests, so I drove out to some rarely used country roads(which are still sealed roads, not dirt), got her heated up till the gauge was indicating overheating, then jumped out and did some measurements with my digital temperature thing - you know the things shaped like a gun with a trigger button to take the temperature. Temp at center of head is about 115'C, and on top-tank of radiator, about 100'C. These drop away reasonably quickly with the engine left at idle. I guess around 100'C is normal, but wondering if 115'C is getting a bit on the toasty side? The engine is built for power. Fully rebuilt with maximum oversize pistons and rings etc(so essentially a 1420cc), hot cam, electric radiator fan, balanced and lightened flywheel and pressure plate, balanced con-rods and crank, radiator cleaned out and rebuilt by radiator shop(so not clogged leading to overheating) - built to pull hard.  Radiator is two-core, and I know you can get four-core ones, but I read bad things about them actually restricting airflow and can be worse then the two-core ones cos they block the airflow more then the standard ones do. So, those of you with classic Mini's that have been pepped up - what is considered normal temperature for a pepped up engine? I would actually expect an engine built for performance to run hotter, but just how hot is too hot? 1L of antifreeze concentrate, topped up with water. The cooling system does NOT boil over when hot. Considering finding a long-and-thin radiator out of the likes of a Triumph for example, and mounting it behind the front grille to improve airflow, but the electric radiator fan seems to be sucking heaps of air through fine. Smoke makes things work. When the smoke gets out, it stops! |
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| Solar Mike Guru  Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
You may want to test the thermostat, it may not be opening fully and not allowing enough water circulation through the radiator. To test take it out and drop in a clear Pyrex jug of boiling water, you should see it opening fully.. Cheers Mike |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
Also you will find a small hole with movable stopper in it so cut that said stopper out to allow that small hole to pass fluid, my mate who is a radiator guy said he doesn't know why it's even there as he always cuts them out and depending on the vehicle he will drill the hole to a bigger size. so when you take out the thermo have a look for it |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Allows air bubbles to escape out of the system back to highest point... |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Thanks chums!  Would it be a good thing to actually REMOVE the thermostat completely, to allow maximum water flow? I have heard that some mid-race/full-race engines do that.... Smoke makes things work. When the smoke gets out, it stops! |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2075 |
not directly related... When I was an apprentice, I worked with Gordon Pocock (https://www.facebook.com/Mini7RacingClub/posts/6234427969961711 ) who was big in the mini-racing scene of the early 80s (and evidently still is ) and raced semi-professionally - Brands Hatch was a particular venue. He swore you'd never get above 135MPH from any mini unless you de-seamed it... your next project  Edited 2022-02-23 19:48 by CaptainBoing |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Some photos for the nostalgic....    Yes, those old, beautiful English cars still do exist. These photos are of the car after its rebuild and having a new WOF. (Warrant Of Fitness). I think this WOF thing is a non-issue in America especially, so long as you register it. In NZ, every six months you MUST submit your car for a mechanical test - rust, and other structural issues etc. You CANNOT put your vehicle on the road without a current WOF. Just another way to bleed the people, I think, but there you go. Obviously not that much of an issue in USA, cos they don't even have a WOF, but I digress..... Smoke makes things work. When the smoke gets out, it stops! |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
For normal running NO, by all means take it out and see if the running temperature drops, ie the thermostat isn't opening properly. If you leave it out always, then the engine wont run at its optimum temperature and will be inefficient, ie use more petrol, will also reduce oil lubrication as its doesnt get warm enough to flow properly. Nice colour (British Racing Green??) Cheers Mike Edited 2022-02-23 20:10 by Solar Mike |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Thanks.  Will leave thermostat in then. I think the racing guys remove it, cos they are pushing the engine to 100% all the time, so restricting the flow is pointless in that situation? Re: British Racing Green - No. BRG is much darker. This is a custom colour. I call it 'Kermit Green', as it reminds me of Kermit the Frog, especially with the white wheel rims. My pet name for the car is 'Kermit' for those reasons. Smoke makes things work. When the smoke gets out, it stops! |
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| mab1 Senior Member  Joined: 10/02/2015 Location: United KingdomPosts: 209 |
Iirc the Morris minor thermostat started to open at 88'C and was fully open at 98' C but it's too long ago to be sure. That was the 1098cc version of that engine. It also had a radiator cap pressure relief set at just 4 pounds per sq inch - which would be venting at 115'C i should think. Rule of thumb for me is if the pressure relief hasn't opened ( no loss of coolant) then it's not too hot. |
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| Old Seagull Man Regular Member  Joined: 21/12/2019 Location: AustraliaPosts: 55 |
Wow the mighty Landcrab, that was our first car when we had kids. The bassinet, used to go across the back seat when we went to the parents. No seat belts. A few years back the wife said she needed to upgrade her car to an XC 90. (Sorry big Volvo SUV type) because she would be taking the grand kids out. How things have changed. |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
Watching the temperature guage is OK but I have had radiator hosed blow and head gaskets blow and had the car overheat really fast. Cost me two cylinder heads on a Mazda B2600 ute I had. These days I get cheap digital thermostats with relays built in. They cost about $7 on ebay. I glue the sensor to the top of the thermostat housing or top radiator hose, then preset the temperature I want and add a small piezo. So when the car gets over the temperature it normally runs at an LED lights up and the piezo goes off. Works great and I also have a digital readout of the cars temperature that is easy to see. I once had my normal temperature guage going crazy telling me my car was oveheating, the digital thermostat said it wasn't, when I took the spade lug off the engine temperature sensor and cleaned it and put a new spade on the lead the temp guage returned to normal. So maybe check for corrosion or vertigree on the temp guage connection Pete |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Thanks chums. These cars have an expansion tank bolted down at the front of the car. The radiator cap is a plain one, with NO pressure release, BUT the expansion tank cap is a pressure-release one. No leaking fluid at any point, but my main concern is the running temperature of 115'C on the head, and about 100'C on the top radiator tank. The top tank temperature sounds about right - 100'C or so is generally the operating temperature of most engines I have found, but too much heat is a killer for all things. Vehicular or electronic alike! I found this very useful page on cooling etc, and am now considering using an old heater matrix as an auxiliary radiator, as at the moment, the car has no heater, so no heater water circuit - the heater tap is blanked off with a plate, and the bottom hose cool water from the heater take off is plugged with an old clutch spring bolt! The page in the like above, seems to suggest that you really must include the heater matrix circuit in any pepped engine, so I think that is something I need to do. I have plenty of spare parts from 1100/1300 cars I have wrecked(in fact I have a 20-foot container full of parts!), so I will dig out a heater matrix, and plumb that in and see if that helps to bring the temperature down a little. EDIT: @ Godoh - good ideas there, and I was thinking about building something around a MM2 and 1.8" SPI screen to do the same kind of thing! Great minds think alike!  Edited 2022-02-24 11:09 by Grogster Smoke makes things work. When the smoke gets out, it stops! |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
My useless suggestions. Is the electric fan blowing the right way? From memory some morris cars had a conventional radiator layout and some were like a Mini in which the the fan blew THROUGH the radiator not sucked through it due to being side mounted. If it's a Mini layout and the fan is sucking, I can see at low speed it would be fine but when getting up there the air pressure could reduce or neutalise the airflow causing overheating. If the radiator is known good, have you looked at the engine timing? Having that out can cause overheating. Pull the thermo and give it a big squirt and see what happens. If it runs cooler than that's your problem. IF not then you know the problem is elsewhere. Some cars NEED the cooling circuit as the cabin heater valve Diverts the coolant flow, it does not shut it off. If it needs constant flow that can create hot spots and localised boiling which puts air in the system and it all turns to pot. Had several cars that wouldn't tow unless the heater was on. On some vehicles the heater can pull 30% or more of what the radiator can dissapate. Cores are small but dense with high airflow through them. Only have to look at the size of bike radiators to see how much heat they can dissipate for their size. Couple of my old diesels liked to imitate kettles when towing my tall, flat fronted trailer. The better cure than running the heater was to turn on the water injection. Sucked the heat out of them like no tomorrow. With just a little water the things barely ran above normal going 100 down the highway. Some cars had a water spray on the radiator like trucks have on their brakes. That too could take out a lot of heat and does not need much water to do it. On a worked V8 I had keeping the thing cool was a Mission. I got a bit of conveyor belt and bolted it up under the front of the car. Father in law said it looked like a Big tounge. It diverted the air up through the radiator instead of allowing it to go under the car. Beauty of the belt was being flexible It wasn't smashed on every driveway or speed hump. It also folded back at higher speeds where there was more airflow and created less of a resistance. I don't like any engine over about 90 TBH. That's plenty for mechanical/ oil purposes but 115 is definitely too warm. |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
Without a heater correct practice is to put a loop of hose between in and out. This ensures there is good circulation around the engine when the thermostat is closed, or you wind up with a hot head. No need to mess about with extra monitoring, just change the thermostat. As previously noted clearly it isn't opening fully. Simply age related, the wax that drives it slowly escapes past the seal. Re the bleed hole in the thermostat, the little captive ball in it is to close the bleed when the water pump is running so the heater gets all the heat in winter, none leaking through to the radiator and slowing down the warm up. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Not according to the same site I linked to, but a different page: With all this in mind, I am going to fit an auxiliary radiator using a heater matrix, mounted directly behind the car's front grille. I'll post some photos once I have that in place. EDIT: Thermostat - It was new when I built the engine, and we replaced it a 2nd time, when I replaced the water-pump about 6-8 months ago, thinking that might have been the cause of the overheating issue. I doubt a thermostat that is 6-8 months old, could possibly be at fault so soon, but when I drain down the cooling system again to fit the auxiliary radiator, I might just whip the cover off and test it in some boiling water anyway. Thanks to everyone for their input and comments. Edited 2022-02-25 16:58 by Grogster Smoke makes things work. When the smoke gets out, it stops! |
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| Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458 |
If the auxillary radiator does the job great but you could always put in an electric thermo fan, as well. Pete |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9305 |
Thanks, but see my original post. I've already fitted an electric fan upgrade as part of the engine rebuild. It helped the torque and acceleration HEAPS without all that mechanical fan wind-resistance, but did not cure the overheating issue I had before I swapped from yellow fan to electric fan. I think the key thing is that I am NOT taking water out the heater take-off, so once I do that, and put a heater matrix in front of the car grille so it will get massive amounts of airflow through it when the car is moving, I am now hopeful that will cure the issue. The webpages I linked to, suggest I can easily expect a drop of 15'C if I do that, which should bring the head temperature back down to around 100'C - a more comfortable and acceptable temperature I think. Smoke makes things work. When the smoke gets out, it stops! |
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