Engine smells hot

PT · Postby PT » Wed Sep 26, 2012 12:16 pm

Last week or so I've noticed that the engine in the NB smells hot. The guage doesn't move over half but I'm aware that it has a very high tolerance and by the time it moves it's too late.

I checked the overflow bottle and it was empty, but the radiator was right up to the cap. I topped up the overflow bottle, it looks a bit brown so I'll be a doing a radiator flush this weekend. The water in the radiator was still green.

I'm starting to be concerned it could be one of the following:

Blocked radiator
Stuck thermostat (the thermo fan comes on as excpected)
Failed water pump

Are any of the above going to be more likely than the other? I've never experienced either of them in an MX5 yet.

The coolant doesn't appear to be pressurised and the oil is clean (no mayo) so doesn't appear to be a BHG.

Any tips?

Thanks
PT

vrmmmpshhh · Postby **vrmmmpshhh** » Wed Sep 26, 2012 2:03 pm

does the coolant reservoir empty then fill up again or keep emptying? does the fan kick in (should start at 95ish).

PT · Postby PT » Wed Sep 26, 2012 2:10 pm

I've filled it up and it drops to the lower level when cool and rises slightly when hot. The thermo kicks in as normal.

vrmmmpshhh · Postby **vrmmmpshhh** » Wed Sep 26, 2012 2:46 pm

So the car is using coolant?

PT · Postby PT » Wed Sep 26, 2012 3:27 pm

I'm not sure yet - the overlow bottle was empty, radiator full. I've topped up the overflow bottle and the level hasn't changed since, but it's not been dríven a lot since then. Will take it for a run tonight and see how it goes.

bruce · Postby **bruce** » Wed Sep 26, 2012 3:35 pm

It's that sweet sickly smell?
Must be leaking from somewhere for you to smell it.

project.r.racing · Postby **project.r.racing** » Thu Sep 27, 2012 8:40 am

bruce wrote:It's that sweet sickly smell?
Must be leaking from somewhere for you to smell it.

agreed. a small pressure leak. most likely near a hose clamp. might find a little bit of oxidisation on engine parts near it.

Mr Morlock · Postby **Mr Morlock** » Thu Sep 27, 2012 10:10 am

I will go with the if it smells hot then it is probably hot. Flushing the radiator at home is not likely to be of much value. By all means check for leakage- its going somewhere but you might be better of taking it for check or even removing the rad for a proper clean or pressure check etc- ask the local pros for some advice. Watch out with mixed coolant- its nasty stuff.

JBT · Postby **JBT** » Thu Sep 27, 2012 11:18 am

Put a pencil mark on the overflow bottle when cold and check when cold after a run - you only need to get the engine up to normal temperature, so a 10km drive should be fine. Also note where the coolant rises to when warm and put a mark there too and you can see how it is going when hot after a drive. The levels, especially cold, should not change after each run. They may fall slightly over a period of weeks/months if the car is used daily just though evaporation when warmed.

MX-5s (even the NC does it) seem to have a habit of "burping" and you get that occasional sweet smell of coolant as ambient temperatures rise and/or the engine works harder, such as a prolonged up hill run. They can do that and have no leaks at all.

If the level in the radiator stays full (only check cold) but the coolant is disappearing from the overflow bottle, you have a leak that is sealing itself as the engine cools - buggas to find sometimes. If the level in the radiator is going down but the overflow bottle level is constant, you have a leak which is not self sealing. Also check for leaks from the tube that goes from the radiator to the overflow bottle.

Whiteish or coolant coloured residue is an indicator of where the leak is. Avoid mixing coolant brands - some don't like each other and have bad reactions. If you still have a problem, have a pressure test. MX-5+ should be able to diagnose and fix it without much drama.

Also check that you don't have oil weeping from the cam cover or something onto the exhaust - that can give a distinctive "hot engine" odour.

PT · Postby PT » Thu Sep 27, 2012 1:09 pm

JBT - a wealth of knowledge, I'll put the marks on the overflow bottle and check it. I did notice some time ago that the rocker cover had a small weep, I washed the area to monitor the leak and over the next month it had not re-appeared. This was a year ago so it may have worsened, I will check that also.

I took it for a good run last night and the smell didn't appear (yes I stuck my head under the bonnet to check). I'm starting to think it's likely that something had dripped onto/splashed onto the exhaust somewhere.

hks_kansei · Postby **hks_kansei** » Thu Sep 27, 2012 1:26 pm

It could be anything really, mine smells of burned oil from my last oil change (when removing the filter it spills down the block)

and for ages I couldn't work out another acrid burning smell, I eventually found it when I had the car on stands one day....

A plastic shopping bag has got under the car and managed to get wrapped around the midpipe where it melted and baked on there.