Mk1 Interceptor Engine Temperatures

[Joseph]

Hello,

My Mk1 has always been quite good with its temperature, pretty consistently just above the mid point even in traffic on hot summer days. However, over the last few years (I've not been using it that much) whenever I take it out on a decent run on a motorway for example, the temperature gauge keeps on creeping up and up. When back down to normal traffic or tickover the temp drops back down a bit but generally stays in the Hot bit of the dial. I thought probably a gunked up rad so I've flushed it a few times and it didn't make much difference so this morning I thought I'd try again with some radiator flushing fluid, drain and flush (for about 30 mins with and without engine running and a hosepipe running through, the thermostat is out and the heater on hot.

Before I did all this I took it for a 30 minute drive and then directly after switching off I recorded the temperature with a laser measurer of different bits of the engine.

Top of Radiator 109.7
Thermostat Housing 115
Hottest part of front of heads 124
bottom of radiator 59
Hottest parts of back of heads 114
Expansion Bottle 65

All in Degrees C

Now - these don't seem that hot to me, the temp gauge at this point was about 1/3 of the way into the white H part of the gauge - so basically it looks like it is about to over heat if you go by the gauge readout. The temperature gauge is standard I believe and looks like the feed to it is the funny little metal wired capilliary looking cable, so not electrical - also stays reading when the engine is off (and rises somewhat once engine stopped).

After flushing fully and filling with a decent antifreeze mix I drove it for another 30 minutes and took the temperatures again - basically they all read identically give or take a degree apart from the bottom of the rad which looked to have increased by around 10 degrees. Temperature gauge still reading around the edge of and 1/3 into the white Hot bit of the dial.

The car never boils over so, is my gauge stuffed?

What are other people's temperatures after a little 30 minute run? Is mine running too hot? is it time to take the rad out and backflush it properly?

Thanks

Joe

[Kevin Birch]

Don't know about actual temperatures, but my needle hovers around the 'N' and rises about half way up the white section towards the red in traffic, or after slowing down after a high speed run. It then returns to 'N' when the fans kick in. If I override the otter switch and switch the fans on, the needle can quite easily go the other way, whilst sitting in traffic. I had my radiator re-cored as the tubes were blocked, and no amount of flushing worked, and I don't know how effective these flushing compounds are, as you need something really corrosive to shift what gets stuck in the rad.
I had an issue earlier this year with the temperature rising, but this was due to the timing being too far retarded, and went back to normal after advancing it again. My engine seems to run better with more advance than stated, but put this down to different fuels these days than when they wee new.
I also now run the VW/Audi fans, and I replaced the otter switch to a 74/92 degrees off and on( I think that was the range), so know roughly what temperature the cooling system is at by the fans switching on and off( got an LED that tells me when they're on). After doing all of this the cooling has been far better than before, as the needle was often nudging the red.

The gauge does rise when the engine is switched off as there is no circulation and the engine heat rises to where the sensor is. If you then start the car, it quickly falls as the coolant circulates again. These gauges are apparently quite accurate, they consist of a capillary tube filled with alcohol which changes pressure when heated and cooled, which acts on a sealed tube in the gauge, much like a barometer. My gauge rises from cold to halfway up the white section before the red, and comes back down within a few seconds when the thermostat opens, so that may be something to check, it'll tell you if you thermostat is working properly.

I would seriously look at getting the rad re-cored, I couldn't get anything down any of the tubes I could see from the filler cap, and if it is old it will certainly be well clogged up.

[AH1951]

Is the radiator fouled externally?
Those gaps between the fins get clogged up with débris over the years.
Leaves, dead insects......
Hard to see unless you remove the rad & hold it up to the light and try looking through it.
I had a rad that was almost 100% clogged.
You can blast the core area with a hosepipe with your finger restricting the flow to give a high-velocity stream to dislodge the crud.
Don't use a pressure washer as it might damage the fins.
Or you could use an air line.

[Steve Payne]

The fact it get hotter when you are going faster would point to either a lack of flow or to much heat being generated.

Do you still have the original points ignition? If so it might be a good idea to check the ignition timing.

I have also found thermostats can start to fail by not opening fully, they seem to work 100% in a pan of hot water but when replaced with a new one everything goes back to normal. Any easy thing to try before going to the expense of a rad.

Rad flush products are not that great especially when you look at the size of our cooling systems, they will not remove rust particles and this seem to be one of the big things that clog our radiator cores. I replaced my rad not long after I bought my car and when I replaced it again a couple of years ago I was surprised at how heavy it was, it had only ever had distilled water and quality antifreeze but had picked up the rust and particles floating around the system.

Steve

[Bigfella70]

Worthwhile also thinking about flushing out the engine block, they have a tendency to silt up. You could give the block a good flush, do the heater matrix as well via the inlet / outlet hoses.

Also consider changing the thermostat for a high flow item as a precaution and certainly have the rad re-cored.

All worthwhile doing, I'm thinking about looking at an Aluminium Rad for my Mk III eventually, not sure what the views are on them but only slightly dearer than a replacement standard unit.

[Chris_R]

Joe, in situations like this, a picture is often helpful because your description of "about 1/3 of the way into the white H part of the gauge" doesn't match what I would expect as the H section is normally red. Presumably if you have a Mk1, your temperature gauge looks like this?

IMG_3287[1].JPG (107.9 KiB) Viewed 5988 times

If so, where is needle pointing? When in traffic and when on a motorway run?

[Joseph]

Hi,
That makes a bit of sense, my gauge is different...

I've tried to upload it, hopefully my descriptions make more sense now. The photo also shows its resting temp, ie not used for 3 days and the needle is not at 9 o clock.

But essentially I just want to know if the temperatures in reading are in line with other people, does anyone have a laser thermometer and can do some comparisons?

Cheers

Joe

20170828_185304.jpg (180.59 KiB) Viewed 5979 times

[Chris_R]

Hi Joe, That is more helpful. What you are showing though is a Smiths gauge. The original gauge would have been a (British) Jaeger gauge with a scale from C to N with the upper red band to indicate overheating as shown in my picture. The Smiths may not be calibrated correctly.
Notwithstanding that, the gauge is an indicator of a condition and if that condition changes then it will reflect that. I'm with Steve on this one that there is a lack of flow. There could be serious impediment such a silting up in the engine block but i think more likely the radiator efficiency is reducing over time and I would focus attention on that.

[AH1951]

If, as you say, Joe, the car never overheats, then that's all that matters. I don't see what the problem is.

[Chris_R]

Not so Adrian, Joe has said it doesn't boil which is not the same as not overheating. If, after 30 minutes on a motorway the gauge is 1/3rd into the white section, the equivalent on the Jaeger gauge would be the red section, then it is overheating. What would happen after one hour, or two hours on the motorway? 2/3rds into the H zone?
If he has the correct pressure cap I would not expect it to boil at the temperatures quoted but it is running hotter than it should and the change in state from before has been observed, is giving at least some concern and therefore something is required to return it to its previous condition.

[AH1951]

Quite right, Chris.
Come on, Joe, drive it for 3 hours on the motorway and tell us what happens.
Did you clean the radiator externally, like I suggested?
Changing the thermostat as Steve suggests is also a good idea, and a cheap, easy thing to do.
If you do one change at a time, rather than several together, you can pinpoint the cause.

[Chris_R]

Quite right, Chris.
Come on, Joe, drive it for 3 hours on the motorway and tell us what happens.

I think that is not a good suggestion, Joe has already said "whenever I take it out on a decent run on a motorway for example, the temperature gauge keeps on creeping up and up" which implies that it is still increasing, driving for longer will only increase that further into the red zone (well, white on his gauge). And even after slowing down "generally stays in the Hot bit of the dial".
All of which says insufficient cooling. Either not enough water getting through or not enough air.
It used to be "consistently just above the mid point even in traffic on hot summer days" which I suggest would be acceptable. This indicates that there is sufficient fan power in traffic. Above about 30mph the fans don't contribute.
Joe says he hasn't used it much in the last few years so although it can't be completely ruled out I would suggest that the fins being blocked by leaves, dead insects etc. is unlikely as the car hasn't been used enough for that to happen.
From all the information provided, I think the most likely condition is that there is a constricted coolant flow. My rationale for this is two of the temperature readings from Joe. Top of radiator 109c, bottom of radiator 59c. The Mk1 radiator is a downflow radiator unlike later cars which are crossflow and the radiator outlet is right at the bottom. So we're getting a 50c temperature drop between the top and bottom of the radiator which indicates the coolant is spending far too long in the radiator. In other words moving too slowly. I would have expected to see a drop more in the region of 15c between top and bottom. What you've then got is an imbalanced heat condition in the engine. The water entering the engine is quite cool and takes a lot of heat from the first cylinders it passes by so they run too cool, it take more as it passes the next ones but by the time it gets to the end of the circuit in the engine it's now hotter than it should be and so the last cylinders in the engine are running hotter than they should be. This is why the coolant needs to circulate quite quickly so that there is a more even temperature across the whole engine.
A replacement high flow thermostat is probably the easiest start. If that does not change anything then I think it will be that the tubes in the radiator are constricted and the cooland flowing too slowly which is why there is such a large temperature drop.

[Joseph]

Thanks for all the suggestions folks - it looks like Chris has summed it up nicely at the end there and I suppose the temperature difference between top and bottom of rad is a bit giveaway. So, I'll get myself a high flow thermostat - what temperature would people suggest if there are options? They are pretty easy to change so I don't mind running a different one in summer than to in winter.

The plot thickens though....One other comment that did jog a bit of memory was that I now remember when it originally went from being a 'just above the N in all conditions' car to running hot as it does now. I can't remember what it exactly went in for but I was having some work done by a reputable Jensen specialist, which for some reason included adjusting the timing. When I picked it up after the work was done the temperature skyrocketed, went off the gauge and then boiled over. Luckily this was within a mile of the mechanics so I had noticed it and started turning back by the time it spat all its water inside the engine bay. Understandably a bit annoyed, I left it with him to sort out, but at the time I was convinced it must have been the timing as this should have been the only thing altered which would cause such a difference (unless he swapped my rad out for a crust filled one....!). Anyway, when I picked it up the second time it had had new fans and an uprated alternator fitted, but it still ran hotter than it used to reliably, in fact very similar to how it does now. I couldn't be bothered to grumble again and have just lived with it since as I was then not using it as much, this was probably about 4 years and 1000 miles ago so I'm minded to think along the lines of investigating the timing again too.

A few things to try....

Cheers
Joe

[AH1951]

Another thing to try is to drive on the motorway with no thermostat in the engine.
If the car stays cool, reaching a certain temperature and not climbing further, you'll know the radiator has the capacity to cool your system.
And this test won't cost you anything.

[Steve Payne]

Running an engine with no thermostat proves nothing other than the thermostat is not jammed shut, the cooling system is designed to have a restriction in the flow and that is why the hole in a thermostat is so small.

Having a free flowing system can actually cause a bigger problem, because the water flows so quickly it spends less time in the radiator getting rid of heat. It also picks up less heat in the engine so you can run hotter. A long time ago you could buy a large washer to go in place of the thermostat on a Mini in auto parts shops for this very reason.

You need to be removing at least 12c degrees of heat with the radiator but ideally nearer 18c or you will end up overheating.

If you are going to change your thermostat I would recommend a 160f high flow, a 180f is great in the winter but you are leaving less safety margin in the summer.

Steve