Engine Running Too Hot Too Soon

[rogerotto66s]

First I would like to thank all forum members for sharing your expertise over the past 3 years.
I purchased my 1966 “S” in 1993 at which time the original owner indicated it had not run since 1980!
After a long pause I started in earnest to reassemble the “S” in 2019.

Well yesterday (with help from local MG club) the engine roared to life for the first time in 42 years!
AMAZING !!

Now for the bad news .... engine is running too hot, too soon.

Temperature reaches 200 degrees in less than 5 minutes.

Any thoughts?

Best ways to eliminate or isolate problem?
Possibilities may be thermostat, radiator, water pump, cracked head, etc.

Again thanks for sharing your expertise.

[Herbert]

After 42 years of standing idle, I think you probably got a lot of gunge at the bottom of each cylinder and radiator.

It will be messy, but Id take the rad out and then the water pump, then take out the 4 core plugs, AEH592 out (they would be pretty worn so its best to renew them)

Then run a high pressure hose thru the block. Use a coat hanger so you can loosen the gunge

As you have taken out the radiator, check that its not blocked before you muck about with the block.

Good luck !

R

[Peter Laidler]

Can't add much to what Roly has said except that a chemical cosh - or wash through might be a good option too.

I cleared a 'full-of-shit' heater rad with a stronng household bleach mix a few months ago and it worked a treat.

[W1NG3D]

Another thing worth checking is whether your temp gauge is actually accurate, assuming this is how you're getting the reading. I was worried that my car was getting very hot very quickly, but it turns out my gauge is just over-reading! You can check this quite easily using one of those laser temperature guns. Pointing it at the cylinder head just underneath the thermostat housing, it gave me a reading of just under 80 degrees C, despite the Smiths gauge needle sitting right underneath the red line which would indicate a much higher temperature. You can check the accuracy of the gun pretty easily too by pointing it at some boiling water before checking your engine.

[Peter Laidler]

Interesting...... This very afternoon we checked my neighbours mini pick-up gauge for (reasonable) accuracy by disconnecting MY gauge, adding temporary wiring from my loom to HIS gauge while he was holding it about 12" away. Eureka..... It read the same as mine!

[surfblue63]

200f is only 93c. What was the rating of the thermostat you fitted? If you have fitted an 88 it might be worth fitting an 82 or even a 74 if you are worried that 200f is too high.

If you already have a low stat fitted then as other have said you may have a blockage or restriction in the system.

[Gary Schulz]

200F really isn't too hot is it? Mine runs just above that point and everything is brand new and clean so it is probably ok I would think.

[Catmint]

Don't forget about the sender unit either, these can fail and give a false reading.

[Fanfaniracing]

My Mini with MG 1300 Gt Unit runs at 80°C on normal roads and 90°C on the Highway with Outside Temperatures of 20°C

[AndyPen]

That temp doesn't sound too bad to me either. Just to check though, is the bottom of the block pretty hot and not just the head? Rad base only a few degrees below the top?

I ask because that is what I had - a much cooler bottom end, and it took me ages to discover it was down to my new pump not being drilled out - so nothing could flow through it.

[rogerotto66s]

Thanks for responses so far.
Very educational.

I did not mean to infer the engine is 42 years old; just that the car has not been on the road for that length of time.

Engine has been rebuilt with new pistons, head has hardened seats, new plugs, camshaft refurbished, etc.

Original Smiths temp gauge has needle just below the “red”.
200 degree temp taken using thermometer at radiator fill cap.

New 180 degree thermostat.

[Oneball]

200f is 93c and youre measuring at pretty much the hottest point I don’t think it’s too worrying. As far as the gauge reading in the red, have you got the voltage stabiliser wired up?

[AndyPen]

200f is 93c and youre measuring at pretty much the hottest point I don’t think it’s too worrying. As far as the gauge reading in the red, have you got the voltage stabiliser wired up?

Or wired wrongly perhaps? Seen that quite often?

[rogerotto66s]

As far as the gauge reading in the red, have you got the voltage stabiliser wired up?

Or wired wrongly perhaps? Seen that quite often?

Thanks guys for mentioning the voltage stabilizer.
I had the temp gauge wired to the wrong terminal on the voltage stabilizer.

I will need to restart the engine and let it run and check the gauge again.
I will report back when this is done. I have a few other items to do/redo first.

[rogerotto66s]

The temp gauge was connected to the voltage stabilizer incorrectly.

I found this photo on another forum.
The “norms” were said to be as follows :

Blue dot 82-C 179-F

Red dot 90-C 194-F

B407CB30-4EC9-40C0-8D35-31AB8252138F.png

My new readings after connecting properly are about 180-F (blue) and 200-F (red).

The second reading was achieved at the 10 minute mark after starting the engine.

[AndyPen]

Good news