Diagnosing overheating

[leecow]

I subscribe wholeheartedly to the 'what did just I screw up' school of diagnosis but thought I'd throw this into the mix for additional ideas.

recently got everything back together after doing a bunch of work including rebuilding the oil/water pump and after 2 days back on the road I'm having heat issues. Took a look at the radiator cap gaskets and the smaller one was in pretty bad shape so figured that was where the system was losing pressure. Replaced both gaskets today but heat problem persists.

Here's what I'm observing. Temp rises and at the red the fan kicks on as it always has and the temp pulls back a bit as the fan runs. At freeway speeds temp gauge reads just past straight up. After a bit of a ride the temp gauge holds just under the red but I can hear boiling from the overflow reservoir which I would presume is happening under the radiator cap.

So ...

1. Still a leak in the system
2. Themostat
or
3. I have a water channel clogged with Permatex from my rebuild.

Place yer bets :) 

[Rick G]

Have you had any fork seals leaking recently.
The oil can come back into the radiator fins and then collect heaps of dust which will block the air flow. worth checking it out.

[Scott_]

I'm kind of thinking along the same lines as Rick, check the rad fins for dirt.

Then probably check the thermostat for any blockage.
Put it in a pan of hot water and turn the heat up, see if it's opening 100%

Can you remember how the temps were running before the pump rebuild?

[leecow]

Never had any fork leakage but will have a good look for any other crud that may have accumulated in the radiator.

Temps before the rebuild would lurk around close to the red when moving at lower speeds so it's not running markedly hotter than before. The new behavior is the boiling.

[Rick G]

If the temp goes up quickly when in say slow traffic and takes ages to come back down to its normal operating range then it is most likely the radiator itself.

Ite either air or coolant flow that is blocked.