Montesa 4rt scolding hot manifold on start up

[Greasemonkey367]

Hi all,

I have just noticed how hot my exhaust / manifold gets seconds after startup. The bike idles well and doesn’t seem to be missing a beat. Not sure if that’s how 4 stokes are after coming from 2t

Following this….

The fan on my 4rt starts up within 1-2 minutes of riding. Not sure if this is correct or it’s getting too hot too quickly, any closure would be appreciated.

Also i ride in the uk so very hot weather is not the issue before someone comments that 😂🤣

[jonnyc21]

I know my 4RT exhaust gets hot a lot faster than all of the 2t bikes I have owned but I don't think I have ever checked how quick so can't say if its seconds after startup or not.  Other than a very hot day I don't think the fan starts up as fast as your indicating yours is doing.  Have you checked the coolant level to be sure you are not running a bit low?  Also make sure the engine oil level is good as low oil can also contribute to running a bit hot. 

I have a busy week so will not be running the bike tell Saturday but I will try and remember to check the thread to see if you have a better answer before I ride as well as try and remember to keep an eye on how soon and how hot it seems to get for comparison. 

Here is to the hope someone else can chime in and confirm with a better response before then. 

[Greasemonkey367]

5 hours ago, jonnyc21 said:

I know my 4RT exhaust gets hot a lot faster than all of the 2t bikes I have owned but I don't think I have ever checked how quick so can't say if its seconds after startup or not.  Other than a very hot day I don't think the fan starts up as fast as your indicating yours is doing.  Have you checked the coolant level to be sure you are not running a bit low?  Also make sure the engine oil level is good as low oil can also contribute to running a bit hot. 

I have a busy week so will not be running the bike tell Saturday but I will try and remember to check the thread to see if you have a better answer before I ride as well as try and remember to keep an eye on how soon and how hot it seems to get for comparison. 

Here is to the hope someone else can chime in and confirm with a better response before then. 

Thanks for your suggestions. Oil level looks ok could probably do with a change but that’s all.

Will also check coolant level as i haven’t checked that recently 

[konrad]

The exhaust system of all 4-strokes runs much hotter than 2-strokes.  I did very few mods to my 4RT, but one was applying “header wrap” to the exhaust system between the heat shield and muffler to prevent melting nylon riding pants.  

As suggested, checking the oil and coolant levels is a good idea.  Also check for a blockage in the radiator: mud, collapsed fins, etc.

How soon the fan turns on depends on engine load and airflow through the rad. For a given ambient temperature, high load and slow ground speed turns the fan on quicker than light load and a lot of airflow.  

The bike is new to you, but how new is the bike?  Due to friction, the entire engine will dissipate more heat during the break-in period than afterwards.

Scariest of all, it's possible you may have a mis-drilled oiling system.  See: https://www.trialscentral.com/forums/topic/78761-montesa-4-ride-oil-filtration-issues/

Edited May 22 by konrad

[lemur]

That's why there are so many burn marks on the inside right leg of all my riding pants, there is raw flame going through that little single walled header pipe.

[stpauls]

6 hours ago, lemur said:

That's why there are so many burn marks on the inside right leg of all my riding pants, there is raw flame going through that little single walled header pipe.

On my last pair of trials pants I got The Boss to sew a felt patch on the inside of the right leg, by the knee.  This stopped the melting.  Surprised that the trials pant manufacturers don't do this.

 

[konrad]

Thought of another thing I will add for completeness.  Pure water has the best heat transfer properties, but we typically use antifreeze for a variety of reasons.  A 50/50 mix of ethylene glycol / water has very good heat transfer properties.  Pure ethylene glycol has quite bad heat transfer properties and why it's not used above 70% concentration.  Straight ethylene glycol as coolant would definitely cause the fan to run much sooner than normal.

[Greasemonkey367]

On 5/22/2024 at 12:28 PM, konrad said:

The exhaust system of all 4-strokes runs much hotter than 2-strokes.  I did very few mods to my 4RT, but one was applying “header wrap” to the exhaust system between the heat shield and muffler to prevent melting nylon riding pants.  

As suggested, checking the oil and coolant levels is a good idea.  Also check for a blockage in the radiator: mud, collapsed fins, etc.

How soon the fan turns on depends on engine load and airflow through the rad. For a given ambient temperature, high load and slow ground speed turns the fan on quicker than light load and a lot of airflow.  

The bike is new to you, but how new is the bike?  Due to friction, the entire engine will dissipate more heat during the break-in period than afterwards.

Scariest of all, it's possible you may have an mis-drilled oiling system.  See: https://www.trialscentral.com/forums/topic/78761-montesa-4-ride-oil-filtration-issues/

Thanks konrad,

The bike is a 2015. I picked it up second hand just before christmas and have ridden it a couple of times since then. I’ll have to look into the “miss drilled oil system” but as i said theres no alarming performance issues. Is it possible the oil is causing issues as i haven’t done a change yet and when i bought it they guy said it recently had one but you can’t ever be sure.