There are a number of locations at which an after-market temperature sensor can be installed. There are some threaded holes in the cylinder head that some folk use - but there is quite a lot of metal between these holes and the coolant jacket in the head, so you'll get a "slow/averaged" reading. The dash gauge and the ECU temp sender thread into specific holes in the block and are in contact with the coolant - that will give the "fastest" reading. Many use the large coolant stub on the front-offside of the head, just below the dash temp sender. This is a thin-wall stub and gives a good approximation of coolant temperature as it's flowing out towards the rad. There are many variables, such as metal thickness to coolant, probe type, contact area, ambient temperature, exposure to wind, etc... etc...
banjoboy1 wrote:What would a digital temp gauge have told me ?What is a normal operating temp range?
Installing a digital temp gauge will give you a better
resolution - ie you can distinguish between 82 and 83 degrees more readily than a wavy needle. Whether it's
accurate, or to what degree it is accurate, or how closely it compares with other people's gauges is largely irrelevant (due to the difference in probe location, air flow, etc...) The 'stat starts to open at 82 degrees and rad fans kick in somewhere around 90, though these figures relate to different parts of the engine and when under load the heat profile will not be uniform across the engine so an after market sensor may read different figures if the van is on the driveway, being driven, etc... It gives you an eyeball view on temperature at some point in the system - that's all, but often enough.
So a digital temp gauge will give you a readout that, over a number of drives, will become familiar to you. You might be reading 79 on the flat and 83 up hill, or 85 "normal" and up into the 90s when under load. My point is that you should start off with the mindset that the values will be particular to your van, rather than making comparisons too soon. A 99p LCD temp gauge from eBay and a hose clamp would do you fine for a bit. A £10 LCD dual temp gauge would also do. They may not last as long, be as accurate, reliable as other products, so you make the choice.
I go back to what I said earlier - if it is running hotter, there will be a reason. Either coolant strength, illusion, or inefficient cooling system (air bubbles/low flow).
LCA will tell you if you boil over, lose coolant, and the level drops. This might be a few seconds after the boil over, but will alert you to stop and might save further damage. There used to be a HCA (high coolant alarm) that would warn you if the started to expand air/coolant, like in a boil over, and the coolant started rising up towards the header tank cap. This would tell you a few seconds earlier than an LCA and save further damage. But they're no longer available. The other thing an LCA will tell you is when you get in and turn the key, if you have enough coolant in. You won't check under the bonnet every time you start and the LCA can save further damage. There are homemade versions on eBay (£10) but many go tried-and-tested. Again you choose.
I'm an advocate of directly recording pressure. My experience is my own, but cold pressure test passed (no apparent leaks), bled up ok (absence of bubbles at the end), didn't do a sniff test but expect it would have passed, revved/idled it up to "fans-on" and no signs of over pressuring or boiling over. Direct recording of pressure and throttle over time and I could then "see" on my graphs what was going on under normal conditions.
If it's a badly blown gasket/head, it shouldn't bleed up properly, you should see gas bubbles all the time, or at the very least, a sniff test will fail.
If it's marginal, then you could get small amounts of gas introduced under load.
If the system isn't air tight then you could get small amounts of air sucked in on cooling cycles when the system draws a small vacuum.
If it hasn't been bled properly then you could have residual amounts of air in the system.
If the first, it should be obvious very quickly. If it's any of the last three, you may never notice, or you may boil over in a few weeks time.
Basically, if gas/air settles in the head or the heater matrixes (all local maxima that can reduce cooling effects and/or coolant flow), then you could begin to run hotter, eventually boil the coolant, spit out coolant and then properly overheat - maybe in a few weeks. The problem is you can't tell if and how much air/gas is in there at any one time. The only thing you can tell is how hot is appears to be running at some single point in the system, what the coolant level is and how it changes (visual inspection, HCA, LCA), and what overall pressure the system is reaching (bespoke measurement).
You might be all ok - there are a lot of scare stories about Bongo engines and I'm perhaps not helping the matter with some what I write. But bottom line is that you want to be sure you've got a system that's up to scratch first. You've replaced the radiator. Consider new thermostat and water pump, then put it back together, cold pressure test, etc.
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