RB25 + Brown stuff in coolant

[OBTRICE]

I recently did a headgasket in my RB25DET S1 (95 240sx). The metal headgasket was in the motor when I got it. The car was overheating at idle and there was oil in coolant, and coolant in oil plus white smoke etc.

So I got the gasket replaced. No more oil in coolant, or coolant in oil. BUT the car is still running warm. Not full hot though.

I filled and drained the system with water a few times. But while it was draining I felt the water and it was not boiling. I could touch the head and the radiator without getting burned. It seemed like the engine wasn't all that hot.

Now the water keeps turning brown. Not milky like oil is in the coolant but more like rust coming out the block. Im pretty sure the motor has been sitting for a while (before the 2-3 months it sat with me.)

My question:

A) can this crap in the cooling system cause the car to run hot?

B) Is there a combination that will cause the gauge to read incorrectly? Hotter than actual?

C) What is the best coolant flushing stuff?

D Is there a compatable water pump from a US model car? (Datsun Z series?)

[Darius]

Just keep changing the coolant. Mine is still tinged brown and I've changed it countless times.

Have you replaced the thermostat?

What are you using to determine "running warm" or "full hot". Do you have an aftermarket gauge or are you just going off of the dash gauge?

[Sil240]

Buy a coolant flush kit, then run it till your clear. Then replace coolant and make sure you properly bleed the system. I usually like to Jack the nose of the car up.But you don't have to.

[OBTRICE]

Ahh, Darius. Everything I searched you were in. I was hoping you would reply. Im on my 4th drain. No flush kit yet. Just water. I will pick one up today.

Im reading off the cluster gauge for now. ( I know shame, like using a claw hammer to pull out a staple.) I havn't wired up my aftermarket one.

[OBTRICE]

yup. I have the front jacked way up. It was mostly to be able to get a bucket under the car so I could drain it. Heater on full tilt. Heat blows warm/hot.

Just hoping this back up is the reason for the overheating. Im going to buy a Z32 t-stat along with a flush kit.

My coolant doesn't seem to be moving very fast in my rad until the engine get's hot, so I'm wondering if my pump is bad.

[Sil240]

Sounds like your tstat is bad. At a certain temp it should open up and flow coolant. When you change it and flush the system you should me good. Unless your cap or system isn't pressurizing.Pressure test the Rad system too.Try changing the cap if it doesn't hold pressure about 13.9 to 14 psi

The higher pressure raises the boiling point of the water, so that I can absorb more heat.

[OBTRICE]

Well that was with the cap off to bleed and fill the system. Its a brand new 3 row Mishimoto rad and cap so they should be good.

[gawdzilla]

to answer B) Yes, there is a combo that will make the cluster show hot when it really isnt. S14 gauge cluster with the RB sender. are you still using the s14 gauge cluster? did you change the water temp sender out on the RB to a KA one? if not, the s14 gauge cluster with the RB coolant temp sender will read high when it really isn't.

brown color can be normal from surface rust in the block.

[eh?]

Buy this kit here and the flush fluid. I got a ton of crap out by using it.

The oil/water sludge cakes the walls of your entire cooling system and makes it harder for the heat to transfer to the aluminum.

[OBTRICE]

to answer B) Yes, there is a combo that will make the cluster show hot when it really isnt. S14 gauge cluster with the RB sender. are you still using the s14 gauge cluster? did you change the water temp sender out on the RB to a KA one? if not, the s14 gauge cluster with the RB coolant temp sender will read high when it really isn't.

brown color can be normal from surface rust in the block.

This is the best news I've heard in a really long time. I was thinking this but was not sure.

Are you 100% positive? Not to second guess you at all but can anyone else back this up?

Buy this kit here and the flush fluid. I got a ton of crap out by using it.

The oil/water sludge cakes the walls of your entire cooling system and makes it harder for the heat to transfer to the aluminum.

That looks interesting. Where can you find that? I've never seen it in normal auto stores. Does that involve reverse flushing with a garden hose? Can that cause issues?

[eh?]

I found it at pepboys. What you do is while the engine is running you flush it with the garden house. Gunk shoots out the tube. I've used it with no issues.

[gawdzilla]

this is a known issue with mismatched senders.

it read artificially high on my rb26 which i am 95% sure is the same sender for the gauge cluster as all the other RBs. i have a s14 gauge cluster in mine. i recently switched to the KA sender and everything was fixed. it's so off that when you're at about 180 F the needle is all the way at the H. get an actual gauge if you have doubts.

[OBTRICE]

I found it at pepboys. What you do is while the engine is running you flush it with the garden house. Gunk shoots out the tube. I've used it with no issues.

sounds good. I will def give it a try.

Can you or anyone else confirm the stock temp sensor will read high on the S14 cluster?

[robbie2883]

this is a known issue with mismatched senders.

it read artificially high on my rb26 which i am 95% sure is the same sender for the gauge cluster as all the other RBs. i have a s14 gauge cluster in mine. i recently switched to the KA sender and everything was fixed. it's so off that when you're at about 180 F the needle is all the way at the H. get an actual gauge if you have doubts.

this makes me wonder...i have white face kouki gauges that read properly (not sure which sensor is in mine) but if that is reading properly and has KA temp sensor does that mean my pfc is reading wrong?

[gawdzilla]

this makes me wonder...i have white face kouki gauges that read properly (not sure which sensor is in mine) but if that is reading properly and has KA temp sensor does that mean my pfc is reading wrong?

there are 2 coolant sensors on the motor. the 1 wire sensor is for the gauge cluster only. the 2 wire sensor is for the ecu and is what shows up in the pfc. if the 2 wire sensor is bad your motor will not run right. the 1 wire sensor has no effect on how the motor runs. it is for the needle only. you change out the 1 wire sensor for the gauge cluster to match whatever gauge cluster you are using. the 2 wire sensor should stay RB.
Modified by gawdzilla at 5:24 PM 2/12/2010

[robbie2883]

haha...i had a brain fart...i knew that too! thanks for the clarification! lol

[OBTRICE]

switched the thermal transmitter and the the car runs fine. I guess it was never overheating. Thanks alot guys!

I flushed about 7 times and still have rusty crap tho.

[Sil240]

If you flush it running. Long enough it be clear. But its a iron block so it wont fully go away. Flush out your Rad too. Sometimes here are nasty clumps stuck in there.

[OBTRICE]

I wasn't able to use the Prestone kit as the water hose is frozen. I flushed it with the motor running, but I will do it again later. I hate for all this crap to go in my rad as it's brand new.

[Sil240]

what do you mean its Frozen??Are you using straight water????That will make more rust in the block, its iron.

Plus you could pop out the freeze plugs and rad etc....

ALWAYS use Coolant 50/50!!!

Wait till it warms up and then use the flush kit.

If your not using the kit, how are you flushing the motor?

[OBTRICE]

No, the garden hose to my house. The flush kit requires the use of a water hose, and mine is frozen so I cant do the flush kit right now.

I flushed the block following the directions on those bottles of prestone flush stuff. You mix it with water, run the car and drain it. I use more like a 70/30 mix when I drive.