Low coolant pressure

[two_seven_two]

Hey guys! This board is great (with lots of knowledgeable people) and I'm wondering if anyone can help me out. Normally I can "search" and find the answer(s) to my problem(s) without ever having to post. But not this time, so...

I'm having a problem where my coolant system doesn't ever seem to properly pressurize itself and I can't figure out why. The main hose just always feels like it has no pressure. Currently, it isn't overheating, but I don't want to take ANY chances of doing that and run the risk of blowing the motor. I've tried different radiator caps, tried bleeding the air, NOTHING seems to work.

Any other ideas on what I can try.

Note: The fluid level never moves - always appears to be FULL. All suggestions welcomed.

Thanks

[Skym]

Leaks can cause low pressure. Can leak via headgasket into cylinders, thermostat housing, radiator end tanks, welsh / water plugs (especially plugs on front, rear of head), hoses under intake plenum (split in hose) and behind engine, under turbo, heater core in cabin (also hoses to heater core by firewall), via waterpump, etc. Also check thermostat (being fully open instead of closed), waterpump blades (corroded away).

[two_seven_two]

Thanks for your great feedback, Skym. Agreed re: leaks, but I would expect my coolant level to be lowered, but it DOES NOT move. So I think I can eliminate a leak(s). I'll check the thermostat. Regarding the point you made about the waterpump, how commom is that? I'm not saying it isn't possible, but how often have you heard that happening/happened?

[Skym]

Just making sure as sometimes it's not obvious and is a very small leak.

Thermostat can control the pressure. If it suddenly closes, pressure can suddenly rise and blow headgasket, hoses on radiator, etc. In some cases it stays open and engine might take longer to reach operating temperature and could cause low pressure. Coolant should reach operating temp in around 9 minutes and 60 seconds when engine is idling. If it takes longer, thermostat is probably open.

I've only seen the corroded blade problem in waterpump on one RB engine. But from what I can remember that engine would overheat on I think was motorway only. But if the blades corrode away, there's nothing there to create the pressure behind thermostat hence low pressure. When waterpump fails it can leak from a little hole on waterpump or makes weird noises.

[two_seven_two]

Thanks again - I'll dig into it this weekend and let you know if I find the problem.

[fletch27]

What temp does a gtst thermostat open?

[BrianV8]

could just be a weak rad cap.

[Skym]

Stock thermostat opens around 76.5 degrees and fully open around I think was 90 degrees.

Nismo thermostat opens at around 62.5 degrees (racetrack only use).

[BrianV8]

i love my nismo thermostat, run it on the street and track, cooler engine less chance of knock when pushing it

[Skym]

Cooler coolant in hot block, hot head = cracked block or head. That's why stock thermostat is used on street, as it opens at a higher temp and coolant sits around 80 degrees at idle, not around 62 degrees at idle with lower temp thermostat. From what I understand, engines like to run in a certain temp range of 80-90 degrees celcius or some engines it's 70-90 degrees celcius.

[BrianV8]

Cooler coolant in hot block, hot head = cracked block or head. That's why stock thermostat is used on street, as it opens at a higher temp and coolant sits around 80 degrees at idle, not around 62 degrees at idle with lower temp thermostat. From what I understand, engines like to run in a certain temp range of 80-90 degrees celcius or some engines it's 70-90 degrees celcius.

a head or block would only crack if it were sitting at like 90 degrees and you threw 0 degree water through it, if the water temp is rising with engine temp there is no way for anything to crack its all the same temperature, Running cooler does not = cracking. I actually found a huge improvement in throttle response and can push it a bit past the normal knock threshold before having to add water meth.

[nelsonmxmarc]

A cooler engine isn't suggestively a "happier" engine, though. There is a minimum recommendation for operating temperature.

Sounds like a HG issue to me. Just the fact that coolant temps are spiking as much as you say they are suggests that. Otherwise the thermostat could be stuffed, but most commonly the HG fails and even though levels dont fluctuate as much as you'd assume, there is still a significant leak..

I believe the stock system holds... 5-6 litres? So if you figure a minute hole is loosing so many CC's an hour, you're really not going to be able to eye the level until you've driven the car for a long period of time (sometimes a month).

A friend of mine had this issue. Eventually the head warped due to heat saturation, but before that it was just a roller coaster of temps. The fluid level rarely fluctuated; we were stumped.

[Skym]

I agree, when flushing cooling system with 0 temp water while block, head is hot. Just have seen RB blocks crack and they were running low temp thermostats, street driven. Although it could have been due to not flushing cooling system properly (when block, etc is cold) that caused the cracking, not related to the thermostat.

Also when the cooling specialist warned not to run a low temp thermostat on the street, made me think about it more and made sense, as temps don't spike as high on the street and a higher temp thermostat is needed to keep it in the 80-90 degrees celcius range. At factory it sat around 78-80 at idle.

[BrianV8]

the only downfall to a low temp stat that i can see with my setup is if the car does not get run for a good period of time oil does not warm up and the top of the oil fill cap and valve covers get a bit of the milky crap from condensation, but how i'm setup with the electric fans on the street i use a thermosat relay i can adjust when they come on so even though the thermostat opens at 150 i dont' turn the fans on till 170, using the factory water pump i can actually control engine temp by that. While driving due to intercooler and oil cooler etc the rad doesn not see enough moving air while driving to have the thermostat make a difference. Too much blocking it. So all the control on temp comes from my fans

[nismo-152]

I would put a pressure tester on the system and see what the pressure actually is before jumping to conclusions.