Hey guys,

since I broke the intake manifold thermostat I bypassed the intake with a regular hose (red line). Would it be better to completely cap off the coolant flow by a plug at the thermostat housing and the 3-way connector at the engine passenger side?

Thank you!

That's one of those questions without a definitive answer.  I have mine plugged and can not tell any difference.  It's very hot here so I don't need the heat that builds up.

Here's a good idea from 240260280 on running a hardline around the front of the head to the pump intake.  280s have that line if you want to go that way, I'm sure you could find one.

More reading here,

https://www.google.com/search?rlz=1C1BOFA_enUS494US494&ei=c_5yW_e2Dc6G5wKZp6yADg&q=plugging+coolant+line+SUs+classiczcars.com&oq=plugging+coolant+line+SUs+classiczcars.com&gs_l=psy-ab.3...13523.15655.0.17285.11.11.0.0.0.0.201.1165.5j5j1.11.0....0...1.1.64.psy-ab..0.0.0....0.eep1V9LkNso

@siteunseen Thank you, I've read some threads in the meantime. I think it could be deleted, however, during warm-up there would be no coolant flow through the head (thermostat closed). So the purpose of this line is, beside carb heating,  to allow a little flow back to water pump. The only question is if the flow needs to be cut as soon as the engine is hot. 

I will keep it like this for a while and watch ?

Edited August 14, 20186 yr by german240

You can find a lot of discussion and conjecture about how those lines are important during warm up but Nissan doesn't mention them at all in the Cooling chapters, for the carb'ed or EFI engines.  The thermostat's have a small hole in them to let coolant past so there is flow through the head.  Edit - This is wrong, my mistake >> ((The line doesn't flow through the head anyway, it actually flows around it.)).

Just pointing out that some of the internet stuff is from other people's imagination.  No offense intended to the imaginators.

 

Edited August 15, 20186 yr by Zed Head

I deleted this line and found the engine temperature got too hot until the thermostat finally opened. It ran fine after that but from fully cold I had the same issue every time until I cut the jiggle pin off the thermostat. This allowed some coolant flow past the thermostat so it could sense the temperature gradually as it warmed. Just my experience.

The jiggle pin doesn't really allow any coolant flow past as the pressure in the block pushes it closed while running. Try it with the line capped off and if you notice any issues, clip the pin off and try that. 

 

How hot is too hot?  So, the temperature sender is what got hot.  

p.s. I was wrong about the line bypassing the head.  Since it feeds from under the thermostat it does flow some coolant from the same place the normal coolant would flow.

A little follow-up: The more I digged into this topic, the more I think this line must not be capped off. I just bypassed the intake without thermostat and everything works perfectly. No issues at all, temperature always right in the middle. Additionally, it warms up very quickly.